What Is Cancer?

The word cancer does not mean just one disease. Cancer is a category of diseases involving the overgrowth or irregular growth of cells into lumps called tumors. If a tumor is malignant, its cells grow out of control and damage healthy parts of the body. Some types of cancer have solid tumors, such as breast, lung, colon, prostate, and skin. Other cancers have liquid tumors, such as those involving lymph glands and the blood.