Colorectal cancer affects the lining of the large intestine and rectum.
The colon is also called the large intestine. The colon begins near the junction of the small intestine and extends to the rectum. The colon has four parts:
Colorectal cancer starts in the lining, or mucosa, of the bowel. It usually develops in one area of the bowel over a long period of time. It occurs on the left side in the descending colon 40% to 50% of the time. The cancer grows along the opening in the colon. It also can grow further into the lining and muscle tissue.
Like other tumors, colorectal cancer can spread to lymph nodes and other parts of the body.
Colorectal cancer is the third most common cancer. People have an increasing risk for it starting at the age of 40. People over the age of 50 account for 93% of colorectal cancer cases.
Experts believe that this slow-growing cancer begins when normal cells in the mucosa become overactive. These overactive cells form a small benign tumor called an adenoma. Abnormal cell changes continue, ultimately turning into cancer. Several genes play a role in colorectal cancer, too.
Some risk factors for the disease are:
Certain foods increase the risk for getting this disease, such as: