Colon cancer develops in the large intestine (colon), the lower part of your digestive system. Rectal cancer develops in the rectum, which makes up the last several inches of your intestinal tract. Together, they're referred to as colorectal cancers.
Rectal cancer begins as small clumps of cells called polyps. Although most polyps are noncancerous (benign), some become cancerous over time. Regular screening to find and remove precancerous polyps can prevent rectal cancer from developing. Changes in your diet and lifestyle — such as healthy eating and increasing your physical activity — can help prevent polyps from forming, greatly reducing your risk of rectal cancer.
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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 linked to a high-fat, low-fiber diet and to a high intake of red meat. Some studies, though, 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.
Many cases of colon cancer have no symptoms. The following symptoms may indicate colon cancer:
Abdominal pain and tenderness in the lower abdomen
Blood in the stool
Diarrhea, constipation, or other change in bowel habits
Weight loss with no known reason
Exams and Tests
With screening colon cancer can be detected before symptoms develop. This is when the cancer 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. This may suggest colon cancer. FOBT must be done along with colonoscopy or sigmoidoscopy to screen for and diagnose colorectal cancer.
Note: Only colonoscopy can see the entire colon. 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 you are diagnosed with 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.
Stages of colon cancer are:
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 has spread to other organs outside the colon
Blood tests to detect tumor markers, including carcinoembryonic antigen (CEA) and CA 19-9, may help your physician follow you during and after treatment.
Treatment depends on many things, including stage of the cancer. Treatments may include:
Surgery (most often a colectomy) to remove cancer cells
Chemotherapy to kill cancer cells
Radiation therapy to destroy cancerous tissue
Stage 0 colon cancer may be treated by removing the cancer cells. This is done using colonoscopy. For stages I, II, and III cancer, more extensive surgery is needed to remove the part of the colon that is cancerous. This surgery is called colon resection.
Almost all patients with stage III colon cancer should receive chemotherapy after surgery for...