About Colon and Rectal Cancer

A closer look at the gastrointestinal tract.

Your colon and rectum are part of your gastrointestinal tract. As you digest food, it moves from the small intestine to the colon (the first 4 to 5 feet of the large intestine) where water and nutrients are absorbed and remaining waste becomes stool. Waste moves into the rectum (the last several inches of the colon) and passes out of the body though the anus. When cancer begins in the colon, it’s called colon cancer; when it begins in the rectum, it’s called rectal cancer. Cancer that begins in either may be called colorectal cancer.

Most colorectal cancers begin as a polyp, an abnormal, fleshy growth in the colon or rectal lining. Many polyps do not cause any symptoms but some may result in blood in the stool or a low blood count. Colorectal polyps are common in people over age 50, and most are benign (not-cancerous). The only way to know for sure if a particular polyp has the potential to become cancerous, is to have it removed and then evaluated by a pathologist.

Detecting and removing colorectal polyps before they become malignant effectively prevents colorectal cancer.


Cancers may not cause symptoms at earlier stages, which is why screening tests are so important. If you experience any of the following symptoms, make an appointment to see your doctor for evaluation:

  • A change in bowel habits — for example, diarrhea or constipation
  • A change in the caliber of your stool — becoming pencil thin
  • Blood in your stool, or rectal bleeding
  • Dark stool (black)
  • Abdominal discomfort, such as pain or cramping
  • The sensation that you need to have a bowel movement, even after you have had one
  • Unexplained weight loss
  • Weakness or feelings of tiredness