Colorectal Cancer: About Colorectal Cancer
This form of cancer occurs when abnormal or malignant cells form in the colon or the rectum, the last part of the digestive system. The colon is attached on one end to the small intestine, and on the other to the anus. It is a long muscular tube that removes water, salt and nutrients from food, leaving waste matter (stool) that is stored in the rectum before exiting the body.
The colon averages nearly five feet in length in adults, and consists of five segments:
• The ascending colon
• The transverse colon
• The descending colon
• The sigmoid colon
• The rectum
Colorectal cancer can affect any of these areas.
Cancer cells usually begin in the inner layer of the lining of the colon, then grow through other layers of tissue of the colon. The seriousness of the cancer depends upon how many layers the cancer has penetrated, whether lymph nodes are involved, and whether it has spread to other sites in the body.
Colorectal cancers are usually contained within the colon, but when they reach advanced stages they may spread to other organs, such as the liver and the lungs.
Most colorectal cancers arise from polyps, growths that form in the lining of the colon. Polyps vary in size from a tiny dot to several inches. The majority of polyps are benign, but it can be difficult to determine whether a polyp is benign or malignant by its appearance alone. Therefore, polyps are removed and analyzed microscopically. This is an important means of preventing colon cancer, as the vast majority of malignant tumors develop from polyps.
Tiny polyps may be completely destroyed by biopsy. Larger polyps are removed by a technique called snare polypectomy, in which a wire loop is passed through the colonoscope and the polyps are cut from the intestinal wall by means of a small electrical current.