Colorectal cancer is the abnormal growth of cancer cells in the large intestine. Colon cancer forms in the longest part of the large intestine, while rectal cancer forms in the last 8 in. (20.3 cm) to 10 in. (25.4 cm) (rectum). Colon and rectal cancers are often referred to together as colorectal cancer because they have so much in common.

Although the exact cause of colorectal cancer is unknown, it almost always begins as small growths called polyps inside the colon or rectum. Polyps can be found with screening tests and are often removed during the same procedures.

Colorectal cancer causes few symptoms in its early stages. Symptoms are usually not noticed until later, when the cancer is harder to treat. Symptoms include abdominal pain, a change in bowel habits, bloody stools, stools that are narrower than normal, unexplained weight loss, and fatigue.

People are more likely to develop colorectal cancer if they are older than 50, have a family history of this cancer, or have rare inherited colon cancer syndromes, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC).

Surgery is usually used to treat all stages of colorectal cancer. Radiation therapy and chemotherapy may also be used.

Recurrent colorectal cancer is cancer that has come back after treatment.