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Cancer & Clinical Oncology
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A Simple Definition, A Complex Disease
cancer 'kan(t)-s r n. General term for more than 100 different diseases characterized by the uncontrolled, abnormal growth of cells.
While often thought of as a single disease, cancer is actually a group of more than 100 different diseases characterized by the uncontrolled, abnormal growth of cells that can spread throughout the body. Cancer begins when normal cells in the body live beyond their normal lifecycle, enabling them to continue to divide and reproduce uncontrollably.
Most types of cancer cells form a lump or mass called a tumor, although some cancers such as blood cancers, do not form tumors. Not all tumors are cancerous, or malignant. A tumor that is not malignant is called benign. Benign tumors do not grow and spread the way cancer does and are usually not life-threatening. However, cancerous tumors can invade and destroy healthy tissue. Cells from malignant tumors can also break away and travel to other parts of the body where they can continue to grow. This spreading process is called metastasis. When cancer spreads, or metastasizes, it is still named for the part of the body where it originated. For example, if breast cancer spreads to the lungs, it is still referred to as breast cancer, not lung cancer.
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