The colon begins at the cecum where the small intestine enters through the ileocecal valve and is divided into four sections. The ascending colon extends upward to the hepatic or right flexure, which is just under the liver in the right upper abdominal quadrant. The transverse colon runs transversely across the abdomen to the splenic or left flexure lying just below the spleen in the left upper abdominal quadrant. The descending colon continues down the left lower abdominal quadrant. The sigmoid colon forms an S-shaped loop that extends down into the pelvis and joins the rectum, which in turn joins the anus.
Cancer can develop in any of the four sections of the colon or in the rectum.
Presenting symptoms may vary depending on stage and in which section the cancer arises. Colorectal cancer occurs most often in the rectosigmoid region.