The colon and the rectum make up the 'large bowel' which is a 6 to 8 cm wide tube that leads to the anus. It takes mostly already digested food residue after it has passed through the small bowel, and extracts water form it. The rectum stores faeces before it can be emptied. The large bowel wall is made up largely glandular tissue, and it is from these cells that bowel cancer usually arises. The cancer usually develops though a stepwise process developing from normal tissue, into a polyp then on to cancer. The rate at which is occurs is variable.