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Cancer is general term used for describing a group of several diseases that occur in different parts of the body. Each of these diseases is characterized by an uncontrolled growth of abnormal cells.
Under normal conditions, cells in the body reproduce in a controlled manner. When the mechanisms that control this reproduction malfunction, abnormal cell growth generally results in the development of a tumor. Some cancers, however, do not form a tumor. Instead, these cells affect the blood and blood-forming organs, moving through other tissues where they continue to reproduce.
Instead of dying, cancer cells outlive normal cells, and continue creating abnormal cells. Metastasis occurs when cancer cells spread through the circulatory and lymphatic system to other parts of the body, where they replace normal tissue. Although the cancer has spread to a different part of the body, it is still named for the area where it began. For example, lung cancer that has spread to the bone is called metastatic lung cancer rather than bone cancer.
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