Colorectal cancer is the third leading cause of cancer deaths among American men and women. These cancers arise from the inner lining of the large intestine, also known as the colon. Tumors may also arise from the inner lining of the very last part of the digestive tract, called the rectum.
Unfortunately, most colorectal cancers are "silent" tumors. They grow slowly and often do not produce symptoms until they reach a large size. Fortunately, colorectal cancer is preventable, and curable, if detected early.
How Does Colorectal Cancer Develop?
Colorectal cancer usually begins as a "polyp," a nonspecific term to describe a growth on the inner surface of the colon. Polyps are often non-cancerous growths but some can develop into cancer.
The two most common types of polyps found in the colon and rectum include:
- Hyperplastic and inflammatory polyps. Usually these polyps do not carry a risk of developing into cancer. However, large hyperplastic polyps, especially on the right side of the colon, are of concern and should be completely removed.
- Adenomas or adenomatous polyps. Polyps, which, if left alone, could turn into colon cancer. These are considered pre-cancerous.
Although most colorectal polyps do not become cancer, virtually all colon and rectal cancers start from these growths. People may inherit diseases in which the risk of colon polyps and cancer is very high.
Colorectal cancer may also develop from areas of abnormal cells in the lining of the colon or rectum. This area of abnormal cells is called dysplasia and is more commonly seen in people with certain inflammatory diseases of the bowel such as Crohn's disease or ulcerative colitis.
What Are the Risk Factors for Colorectal Cancer?
While anyone can get colorectal cancer, it is most common among people over age 50. Risk factors for colorectal cancer include:
- A personal or family history of colorectal cancer or polyps
- A diet high in red meats and processed meats
- Inflammatory bowel disease (Crohn's disease or ulcerative colitis)
- Inherited conditions such as familial adenomatous polyposis and hereditary non-polyposis colon cancer
- Obesity
- Smoking
- Physical inactivity
- Heavy alcohol use
- Type 2 diabetes