factor
DEFINITION:
1. Any of several substances or activities that are necessary to produce a result, e.g., a coagulation factor (see below). Often, use of the term "factor" indicates that the chemical nature of the substance or its mechanism of action is unknown, as in endocrinology, where "factors" are renamed as "hormones" when their chemical nature is determined.
2. One of two or more quantities that multiplied together form a product.
3. A gene (hereditary factor).
Antihemophilic Factor (AHF) -
1. See Factor VIII under coagulation factor (below).
2. [USP] A sterile freeze-dried powder containing the Factor VIII fraction prepared from units of human venous plasma obtained from suitable whole-blood donors; it may contain heparin sodium or sodium citrate. Used to arrest hemorrhage or to prevent hemorrhage during surgery or other procedures in patients with hemophilia A; administered intravenously.
Coagulation Factors - Substances in the blood that are essential to the clotting process and hence, to the maintenance of normal hemostasis. They are designated by Roman numerals, to which the notation "a" is added to indicate the activated state. Platelet factors (see below), designated by Arabic numerals, also play a role in coagulation.
Coagulation Factor II, prothrombin - A plasma protein that is converted to the active form thrombin (factor IIa) by cleavage by activated factor X (Xa) in the common pathway of blood coagulation; thrombin then cleaves fibrinogen to its active form fibrin. Deficiency of the factor leads to hypoprothrombinemia.
Coagulation Factor III, tissue thromboplastin - A lipoprotein functioning in the extrinsic pathway of blood coagulation, activating factor X (see below).
Coagulation Factor V, proaccelerin - A heat- and storage-labile material, present in plasma but not in serum, functioning in both the intrinsic and extrinsic pathways of blood coagulation. Deficiency of this factor, an autosomal recessive trait, leads to a rare hemorrhagic tendency, known as Owren's disease or parahemophilia, which varies greatly in severity.
Coagulation Factor VIII, antihemophilic factor (AHF) - A relatively storage-labile factor (see below) participating only in the intrinsic pathway of blood coagulation. Deficiency of this factor, when transmitted as a sex-linked recessive trait, causes classical hemophilia (hemophilia A). (See also antihemophilic factor above.)
Coagulation Factor IX, plasma thromboplastin component (PTC) - A relatively storage-stable substance involved in the intrinsic pathway of blood coagulation; upon activation, it activates factor X (see below). Deficiency results in a hemorrhagic syndrome called hemophilia B, resembling hemophilia A. Called also autoprothrombin II, Christmas factor, and antihemophilic factor B.
Coagulation Factor X, Stuart factor - A storage-stable factor that participates in both the intrinsic and extrinsic pathways of blood coagulation, uniting them to begin the common pathway of coagulation. Once activated, it forms a complex with calcium, phospholipid, and factor V (see above); the complex (prothrombinase) can cleave and activate prothrombin to thrombin. Deficiency of this factor may cause a systemic coagulation disorder.
Coagulation Factor XI, plasma thromboplastin antecedent (PTA) - A stable factor involved in the intrinsic pathway of blood coagulation; once activated, it activates factor IX. Deficiency of this factor results in a systemic blood-clotting defect called hemophilia C, which may resemble hemophilia A. Called also antihemophilic factor C.
Coagulation Factor XII, Hageman factor - A stable factor activated by contact with glass or other foreign surfaces, which initiates the intrinsic process of blood coagulation by activating factor XI and participates in activation of the kinin and fibrinolytic pathways. Deficiency of this factor results in a tendency toward thrombotic disorders, due to lack of activation of the fibrinolytic pathway. Called also glass factor, contact factor, or activation factor.
Heat-labile Factor - See Factor V under Coagulation Factors (above).
Platelet Factor - Factors important in hemostasis which are contained in or attached to the platelets.
Storage-labile Factor - A factor which shows chemically-unstable attributes during storage.
von Willebrand Factor (vWF) - The attribute of factor VIII (see above) necessary for the adhesion of platelets to vascular elements. Deficiency of this factor results in the prolonged bleeding time seen in von Willebrand's disease.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
proteins
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
factor
DEFINITION:
1. Any of several substances or activities that are necessary to produce a result, e.g., a coagulation factor (see below). Often, use of the term "factor" indicates that the chemical nature of the substance or its mechanism of action is unknown, as in endocrinology, where "factors" are renamed as "hormones" when their chemical nature is determined.
2. One of two or more quantities that multiplied together form a product.
3. A gene (hereditary factor).
Antihemophilic Factor (AHF) -
1. See Factor VIII under coagulation factor (below).
2. [USP] A sterile freeze-dried powder containing the Factor VIII fraction prepared from units of human venous plasma obtained from suitable whole-blood donors; it may contain heparin sodium or sodium citrate. Used to arrest hemorrhage or to prevent hemorrhage during surgery or other procedures in patients with hemophilia A; administered intravenously.
Coagulation Factors - Substances in the blood that are essential to the clotting process and hence, to the maintenance of normal hemostasis. They are designated by Roman numerals, to which the notation "a" is added to indicate the activated state. Platelet factors (see below), designated by Arabic numerals, also play a role in coagulation.
Coagulation Factor II, prothrombin - A plasma protein that is converted to the active form thrombin (factor IIa) by cleavage by activated factor X (Xa) in the common pathway of blood coagulation; thrombin then cleaves fibrinogen to its active form fibrin. Deficiency of the factor leads to hypoprothrombinemia.
Coagulation Factor III, tissue thromboplastin - A lipoprotein functioning in the extrinsic pathway of blood coagulation, activating factor X (see below).
Coagulation Factor V, proaccelerin - A heat- and storage-labile material, present in plasma but not in serum, functioning in both the intrinsic and extrinsic pathways of blood coagulation. Deficiency of this factor, an autosomal recessive trait, leads to a rare hemorrhagic tendency, known as Owren's disease or parahemophilia, which varies greatly in severity.
Coagulation Factor VIII, antihemophilic factor (AHF) - A relatively storage-labile factor (see below) participating only in the intrinsic pathway of blood coagulation. Deficiency of this factor, when transmitted as a sex-linked recessive trait, causes classical hemophilia (hemophilia A). (See also antihemophilic factor above.)
Coagulation Factor IX, plasma thromboplastin component (PTC) - A relatively storage-stable substance involved in the intrinsic pathway of blood coagulation; upon activation, it activates factor X (see below). Deficiency results in a hemorrhagic syndrome called hemophilia B, resembling hemophilia A. Called also autoprothrombin II, Christmas factor, and antihemophilic factor B.
Coagulation Factor X, Stuart factor - A storage-stable factor that participates in both the intrinsic and extrinsic pathways of blood coagulation, uniting them to begin the common pathway of coagulation. Once activated, it forms a complex with calcium, phospholipid, and factor V (see above); the complex (prothrombinase) can cleave and activate prothrombin to thrombin. Deficiency of this factor may cause a systemic coagulation disorder.
Coagulation Factor XI, plasma thromboplastin antecedent (PTA) - A stable factor involved in the intrinsic pathway of blood coagulation; once activated, it activates factor IX. Deficiency of this factor results in a systemic blood-clotting defect called hemophilia C, which may resemble hemophilia A. Called also antihemophilic factor C.
Coagulation Factor XII, Hageman factor - A stable factor activated by contact with glass or other foreign surfaces, which initiates the intrinsic process of blood coagulation by activating factor XI and participates in activation of the kinin and fibrinolytic pathways. Deficiency of this factor results in a tendency toward thrombotic disorders, due to lack of activation of the fibrinolytic pathway. Called also glass factor, contact factor, or activation factor.
Heat-labile Factor - See Factor V under Coagulation Factors (above).
Platelet Factor - Factors important in hemostasis which are contained in or attached to the platelets.
Storage-labile Factor - A factor which shows chemically-unstable attributes during storage.
von Willebrand Factor (vWF) - The attribute of factor VIII (see above) necessary for the adhesion of platelets to vascular elements. Deficiency of this factor results in the prolonged bleeding time seen in von Willebrand's disease.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
cancer
DEFINITION:
Any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (the leukemias) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, that occur in the body. However, a cancer differs from a benign tumor, such as a wart or a lipoma, in two important ways. As it grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastases form new, satellite tumors that grow independently.
Incidence
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
Causes
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation--that is, they no longer perform the specialized task of the cells of their host tissue--and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing nothing to their host tissue but continuing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this "occult" phase, metastases may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.
Symptoms
The range of symptoms that may be produced by cancers is vast, depending on the site of the growth, the tissue of origin, and the extent of the growth. Symptoms may be a direct feature of the growth (e.g., lumps or skin changes) or derived from obstruction or bleeding into passageways, such as the lung airways, gastrointestinal tract, or urinary tract, or from disruption of the function of a vital organ. Tumors pressing on or disturbing nerve tracts can cause nervous system disorders and pain. Some tumors lead to the overproduction of hormones, with complications and effects far distant from the site of the growth. Unexplained weight loss is a feature of many types of cancer.
Some important warning signals that always warrant investigation by a physician are: rapid weight loss without apparent cause; a scab, sore, or ulcer that fails to heal within three weeks; a blemish or mole that enlarges, bleeds, or itches; severe recurrent headaches; difficulty swallowing; persistent hoarseness; coughing up bloody sputum (phlegm); persistent abdominal pain; change in shape or size of testes; blood in urine, with no pain on urination; change in bowel habits;
lump or change in breast shape; bleeding or discharge from nipple; vaginal bleeding or spotting between periods or after menopause.
Diagnosis
Both the means of diagnosing cancer at an early stage (when the changes of cure are highest) and the range of treatments available have improved dramatically in the past decade.
Screening tests (for early breast cancer, cancer of the cervix, and intestinal cancer) have cut mortality from these tumors. For most tumors, however, diagnosis generally occurs after the appearance of symptoms, is based on the physician's examination of the patient, and is confirmed by microscopic examination of tissue cells obtained by biopsy; cancer cells look different from the normal cells of the host tissue. New scanning and imaging techniques give more information while causing less discomfort to the patient.
There are four main types of tests: cytology tests, imaging techniques, chemical tests, and direct inspection.
Outlook
Almost half of all cancers are today cured completely, and cure and survival rates for various years after diagnosis continue to improve. For disease of certain organ systems, the diagnosis of a cancer may actually provide a better outlook than some of the alternative diagnoses. Cure and survival rates and the chances of recurrence do, however, vary markedly according to the organ or tissue affected.
