Colon cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon). Such cancer is sometimes referred to as "colorectal cancer."

Other types of colon cancer such as lymphoma, carcinoid tumors, melanoma, and sarcomas are rare. In this article, use of the term "colon cancer" refers to colon carcinoma and not these rare types of colon cancer.

According to the American Cancer Society, colorectal cancer is one of the leading causes of cancer-related deaths in the United States. (However, in almost all cases, early diagnosis can lead to a complete cure.)

There is no single cause for colon cancer. Nearly all colon cancers begin as benign polyps, which slowly develop into cancer.

You have a higher risk for colon cancer if you have:

• Colorectal polyps
• Cancer elsewhere in the body
• A family history of colon cancer
• Ulcerative colitis
• Crohn's disease
• Personal history of breast cancer

Certain genetic syndromes also increase the risk of developing colon cancer.

What you eat may play a role in your risk of colon cancer. Colon cancer may be associated with a high-fat, low-fiber diet and red meat. However, some studies found that the risk does not drop if you switch to a high-fiber diet, so the cause of the link is not yet clear.

Many cases of colon cancer have no symptoms. The following symptoms, however, may indicate colon cancer:

• Diarrhea, constipation, or other change in bowel habits
• Blood in the stool
• Unexplained anemia
• Abdominal pain and tenderness in the lower abdomen
• Intestinal obstruction
• Weight loss with no known reason
• Narrow stools

With proper screening, colon cancer can be detected BEFORE the development of symptoms, when it is most curable.

Your doctor will perform a physical exam and press on your belly area. The physical exam rarely shows any problems, although an abdominal mass may be felt. A rectal exam may reveal a mass in patients with rectal cancer, but not colon cancer.

Imaging tests to diagnose colorectal cancer include:

• Colonoscopy
• Sigmoidoscopy

Note: Only colonoscopy can see the entire colon.

A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, which could suggest colon cancer. However, this test is often negative in patients with colon cancer. For this reason, a FOBT must be done along with colonoscopy or sigmoidoscopy. It is also important to note that a positive FOBT doesn't necessarily mean you have cancer.

A complete blood count may reveal show signs of anemia with low iron levels.

If your doctor learns that you do have colorectal cancer, additional tests will be done to see if the cancer has spread. This is called staging.

• Stage 0: Very early cancer on the innermost layer of the intestine
• Stage I: Cancer is in the inner layers of the colon
• Stage II: Cancer has spread through the muscle wall of the colon
• Stage III: Cancer has spread to the lymph nodes
• Stage IV: Cancer that has spread to other organs