The cells in a benign tumor look like normal body cells. Although benign rumors can grow large enough to interfere with normal body functions, they do nor spread to other parts of the body. Benign tumors that are removed rarely return. Cancerous or malignant tumors can invade surrounding tissue. Through a process known as metastasis, malignant cells travel to distant sites in the body, where the cells can multiply again and form tumors or metastases.
Colorectal cancers arise in the lower portions of the digestive tract.
Figure 1 shows the anatomy of the abdomen, including the colon and rectum. Also known as the large intestine or large bowel, the colon and the rectum absorb water and vitamins from digested food and compact the wastes into feces or stool that is eliminated from the body through the anus. The colon is about 3 inches in diameter and about 5 feet long. The rectum is about 6 inches long leading to the anis. The majority of colorectal cancers arise from the cells lining the inside wall of the colon and rectum.