A cancer is a group of cells (usually derived from a single cell) that has lost its normal control mechanisms and thus has unregulated growth. Cancerous (malignant) cells can develop from any tissue within any organ. As cancerous cells grow and multiply, they form a mass of cancerous tissue—called a tumor—that invades and destroys normal adjacent tissues. The term "tumor" refers to an abnormal growth or mass; tumors can be cancerous or noncancerous. Cancerous cells from the primary (initial) site can spread (metastasize) throughout the body.
Cancerous tissues (malignancies) can be divided into those of the blood and blood-forming tissues (leukemias and lymphomas) and "solid" tumors, often termed cancer. Cancers can be carcinomas or sarcomas.
Because cancer is more likely to be cured if treated early, it is critical that cancer be discovered early. Some symptoms may give early warning of cancer and should, therefore, trigger a person to seek medical care. Fortunately, most of these symptoms are usually caused by far less serious conditions. Nonetheless, the development of any of the warning signs of cancer should not be ignored.
Some of the warning signs are general; that is, they are vague changes that do not help pinpoint any particular cancer. Still, their presence can help direct doctors to perform the physical examinations and laboratory tests necessary to exclude or confirm a diagnosis. Other symptoms are much more specific and steer doctors to a particular kind of cancer or location.
Diagnosis encompasses screening, testing, and a physical examination. After cancer is diagnosed, it is staged. Staging is a way of noting how advanced the cancer has become, including such criteria as how big it is and whether it has spread to other organs.
Common Cancer Types
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