If a doctor finds what may be bowel cancer he or she will perform a biopsy, removing some tissue for examination under a microscope by a pathologist. If the tissue is cancerous, the doctor will want to learn the stage (or extent) of disease. Treatment will depend in part on the stage of the bowel cancer; it is categorized by how far it has spread from its original site. Staging systems for bowel cancer and the terms used by them vary in different parts of the world, and some use letters instead of numbers. One common system used to describe bowel cancer stages is:

Stage AO - very early cancer of the innermost lining of the bowel
Stage A - tumour in the inner layers of the colon
Stage B - tumour in the outer layers of the colon and/or nearby tissue
Stage C - tumour has spread to lymph nodes
Stage D - tumour has spread to distant organs.

There are more details about staging on the Bowel Cancer & Digestive Research Institute Australia web site.

All stages of bowel cancer are usually treated by surgically removing the cancer and possibly some of the surrounding tissue. For Stages B and C, chemotherapy and/or radiation therapy may be added to help kill the cancer and shrink the tumour. Chemotherapy and radiation may also be used in Stage D to improve symptoms and to prolong life.