Colorectal cancer is the cancer in the large intestine and rectum. It occurs when some of the cells that line the colon or the rectum become abnormal and grow out of control. The abnormal growing cells create a tumor, which is the cancer. Cancer that begins in the colon is called colon cancer and in the rectum is called rectal cancer. It is common in both men and women .The risk of developing colorectal cancer rises after age 50.

The colon, the longest part of the large intestine or large bowel, is a long muscular tube shaped organ connecting the small intestine to the rectum. It extends from the end of the small bowel to the anus, twisting and turning through the abdomen (belly). It is divided into four sections namely, the ascending colon, transverse colon, descending colon, and sigmoid colon. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus. The rectum is lower part of the colon that connects the large bowel to the anus. The rectum’s primary function is to store formed stool in preparation for evacuation.

Colon along with the rectum is called the large intestine. Cancers affecting either of these organs also may be called colorectal cancer. Most colorectal cancers arise in the sigmoid colon which is the portion just above the rectum. They usually start in the innermost layer and can grow through some or all of the several tissue layers that make up the colon and rectum. Most colorectal cancers grow slowly over a period of several years, often beginning as small benign growths called polyps. Removing these polyps early, before they become malignant, is an effective means of preventing colorectal cancer.