Colorectal cancer (CRC)–also known as bowel cancer, colon cancer, or rectal cancer–affects the colon and the rectum. The American Cancer Society estimates that about 1 in 21 men and 1 in 23 women in the United States will develop colorectal cancer during their lifetime. 

Cancer of the colon is the disease characterized by the development of malignant cells in the lining or epithelium of the first and longest portion of the large intestine. Cancer of the rectum is the disease characterized by the development of malignant cells in the lining or epithelium of the rectum. The rectum is the portion of the large bowel that lies in the pelvis, terminating at the anus.

Malignant cells have lost normal control mechanisms governing growth. These cells may invade surrounding local tissue, or they may spread throughout the body and invade other organ systems.