Colorectal cancer is malignant cells found in the colon or rectum. The colon and the rectum are part of the large intestine, which is part of the digestive system. Because colon cancer and rectal cancers have many features in common, they are sometimes referred to together as colorectal cancer. Cancerous tumors found in the colon or rectum also may spread to other parts of the body.

Colorectal cancer is the second leading cause of cancer deaths in the United States. However, the number of new cases of colorectal cancer, and the number of deaths due to colorectal cancer, have decreased, which is attributed to increased sigmoidoscopic screening and polyp removal.