14 Jul 2011

Colon cancer

Colorectal cancer; Cancer - colon; Rectal cancer; Cancer - rectum; Aden carcinoma - colon; Colon - adenocarcinoma

Colon, or colorectal, cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon).
Other types of cancer can affect the colon, such as lymphoma, characinoid tumours, melanoma, and sarcomas. These are rare. In this article, use of the term "colon cancer" refers to colon carcinoma only.
Causes, incidence, and risk factors
According to the American Cancer Society, colorectal cancer is one of the leading causes of cancer-related deaths in the United States. However, early diagnosis often leads to a complete cure.
Almost all colon cancer starts in glands in the lining of the colon and rectum. When doctors talk about colorectal cancer, this is usually what they are talking about.
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 60
Are African American of eastern European descent
Eat a diet high in red or processed meats
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
Signs 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.
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
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
Treatment depends partly on the stage of the cancer. In general, treatments may include:
Surgery (most often a colectomy) to remove cancer cells
Chemotherapy to kill cancer cells
Radiation therapy to destroy cancerous tissue
SURGERY
Stage 0 colon cancer may be treated by removing the cancer cells, often during a colonoscopy. For stages I, II, and III cancer, more extensive surgery is needed to remove the part of the colon that is cancerous. (See: Colon resection)
There is some debate as to whether patients with stage II colon cancer should receive chemotherapy after surgery. You should discuss this with your oncologist.
CHEMOTHERAPY
Almost all patients with stage III colon cancer should receive chemotherapy after surgery for approximately 6 - 8 months. The chemotherapy drug 5-fluorouracil has been shown to increase the chance of a cure in certain patients.
Chemotherapy is also used to improve symptoms and prolong survival in patients with stage IV colon cancer.
Irinotecan, oxaliplatin, capecitabine, and 5-fluorouracil are the three most commonly used drugs.
Monoclonal antibodies, including cetuximab (Erbitux), panitumumab (Vectibix), bevacizumab (Avastin), and other drugs have been used alone or in combination with chemotherapy.
You may receive just one type, or a combination of these drugs.
RADIATION
Although radiation therapy is occasionally used in patients with colon cancer, it is usually used in combination with chemotherapy for patients with stage III rectal cancer.
For patients with stage IV disease that has spread to the liver, various treatments directed specifically at the liver can be used. This may include:
Burning the cancer (ablation)
Delivering chemotherapy or radiation directly into the liver
Freezing the cancer (cryotherapy)
Surgery
References

    Burt RW, Barthel JS, Dunn KB, et al. NCCN clinical practice guidelines in oncology. Colorectal cancer screening. J Natl Compr Canc Netw. 2010;8:8-61.
    Cunningham D, Atkin W, Lenz HJ, Lynch HT, Minsky B, Nordlinger B, et al. Colorectal cancer. Lancet. 2010;375:1030-1047.
    Smith RA, Cokkinides V, Brooks D, Saslow D, Brawley OW. Cancer screening in the United States, 2010: A review of current American Cancer Society guidelines and issues in cancer screening. CA Cancer J Clin. 2010;60:99-119. [PubMed]

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