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.
