Colorectal cancer (bowel cancer), is a cancer caused by uncontrolled growth of cells, in the colon, rectum, or appendix. Colorectal cancer is distinct from anal cancer, which affects the anus. Colorectal cancer is the third most commonly diagnosed cancer but it is more common in developed countries.
Colorectal cancers arise from the lining of the bowel (mucosa). If left untreated it will infiltrate the underlying muscle layer and surrounding tissue. Colon cancer usually begins as a small growth of the mucosa known as a colorectal polyp or adenoma. These are usually benign but a small percentage develop into cancer over time. Localized bowel cancer is usually diagnosed at colonoscopy.
Invasive cancers that are confined to the wall of the colon (Stages I and II) are often curable with surgery, In England >90% of patients diagnosed at this stage will survive beyond 5 years. Untreated, the cancer can spread to regional lymph nodes (stage III). Less than 48% of patients diagnosed at this stage survive the disease beyond five years. Colon cancer that has spread beyond the colon and lymph nodes (stage IV) is usually not curable unless the spread beyond the colon is amenable to resection or thermal ablation. Approximately 7% of patients survive beyond five years.