Colon, or colorectal, cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon).

Causes

colorectal cancer is one of the leading causes of cancer-related deaths in the developed world. However, early diagnosis often leads to a complete cure.


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

You have a higher risk for colon cancer if you:

Are older than 50
Are African American of eastern European descent
Eat a diet high in red or processed meats
A diet high in fat and low in fibre.
Have cancer elsewhere in the body
Have colorectal polyps
Have inflammatory bowel disease (Crohn's disease or ulcerative colitis)
Have a family history of colon cancer
Have a personal history of breast cancer

Certain genetic syndromes also increase the risk of developing colon cancer. Two of the most common are:
Familial adenomatous polyposis (FAP)
Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome

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 have found that the risk does not drop if you switch to a high-fiber diet, so this link is not yet clear.

Smoking cigarettes and drinking alcohol are other risk factors for colorectal cancer.
Symptoms

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

Abdominal pain and tenderness in the lower abdomen
Blood in the stool
Diarrhea, constipation, or other change in bowel habits
Narrow stools
Weight loss with no known reason
Exams and Tests

With proper screening, colon cancer can be detected before symptoms develop, 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 the doctor may feel a lump (mass) in the abdomen. A rectal exam may reveal a mass in patients with rectal cancer, but not colon cancer.

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.

Imaging tests to screen for and potentially diagnose colorectal cancer include:
Colonoscopy
Sigmoidoscopy

Note: Only colonoscopy can see the entire colon, and this is the best screening test for colon cancer.

Blood tests that may be done include:
Complete blood count (CBC) to check for anemia
Liver function tests

If your doctor learns that you do have colorectal cancer, more tests will be done to see if the cancer has spread. This is called staging. CT or MRI scans of the abdomen, pelvic area, chest, or brain may be used to stage the cancer. Sometimes, PET scans are also used.




Treatment

Treatment depends partly on the stage of the cancer. In general, treatments may include:
Surgery (most often a colectomy) to remove cancer cells
Chemotherapy(5-fluorouracil and folinic acid) to kill cancer cells