Colorectal cancer usually start in the in the cells that line the inside of the colon and rectum. There are some other, more rare, types of tumors of the colon and rectum. It is more common in people over 50, and the risk increases with age.
Risk factors include polyps (a growth of tissue in the lining that grows into the center of the colon or rectum), a diet that is high in fat, a family history of colorectal cancer, or a history of ulcerative colitis or Crohn’s disease.
Colon and rectal cancers begin in the digestive system, also called the GI (gastrointestinal) system. The digestive system first processes food for energy, then absorbs fluid to form solid waste (stool) and finally passes from the body.
Colon and rectal cancers have much in common. Most start as a polyp (a growth of tissue in the lining that grows into the center of the colon or rectum) and develop slowly over many years. Removing a polyp early may keep it from becoming cancer. In the last 20 years, the rate of survival from colorectal cancer has been increasing in both men and women.