Colorectal cancer is a disease in which cancer cells grow in either the colon or the rectum. The colon and rectum are parts of the body’s digestive system. They remove nutrients from food and store waste until it passes out of the body. The colon and the rectum also absorb water from ingested materials. Normally, the cells in the colon and rectum divide in a regulated manner. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms. A tumor can be benign or malignant.
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A benign tumor is not cancer. It does not spread to other parts of the body. Colon polyps are most often, but not always, benign tumors. Some colon polyps develop malignant cancer in them. Some colon cancers appear to arise from the lining of the colon without a polyp. A malignant tumor is cancerous. Cancer cells divide and damage tissue around them. They can enter the bloodstream and spread to other parts of the body.
Colon cancer is the third most common type of cancer and the third leading cause of cancer-related deaths in the United States. For 2013, the National Cancer Institute estimates that there will be 102,480 new cases of colon cancer and 40,340 new cases of rectal cancer. An estimated 50,830 people will die from colorectal cancer.