The waste matter that is left after going through the colon is called feces or stool. It goes into
the rectum, the final 6 inches of the digestive system, where it is stored until it passes out of
the body through the anus.
The wall of the colon and rectum is made up of several layers (see the illustration in the
staging section). Colorectal cancer starts in the innermost layer and can grow through some
or all of the other layers. Knowing a little about these layers is important, because the stage
(extent of spread) of a colorectal cancer depends to a great degree on how deeply it grows
into these layers. For more detailed information, please see the section “How is colorectal
cancer staged?