Anal Canal Cancer
Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other parts of the body. To learn more about how cancers start and spread, see What Is Cancer?
Anal cancer starts in the anus. To understand anal cancer, it helps to know about the anus and how it works.
The anus is the opening at the lower end of the intestines. It’s where the end of the intestines connect to the outside of the body.
As food is digested, it passes from the stomach to the small intestine. It then moves from the small intestine into the main part of the large intestine (called the colon). The colon absorbs water and salt from the digested food. The waste matter that’s left after going through the colon is known as feces or stool. Stool is stored in the last part of the large intestine, called the rectum. From there, stool is passed out of the body through the anus as a bowel movement.