Colon cancer

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. These include lymphoma, carcinoid tumors, melanoma, and sarcomas. These are rare. In this article, colon cancer refers to colon carcinoma only.

Causes, incidence, and risk factors

Colorectal cancer is one of the leading causes of cancer-related deaths in the United States. Early diagnosis, though, can often lead to a complete cure.

Almost all colon cancers start 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 high risk of colon cancer if you:

Are older than 60
Are African American of eastern European descent
Eat a a lot of red or processed meats
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 inherited diseases 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 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.

Symptoms

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
Narrow stools
Weight loss with no known reason

Signs 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

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

Surgery

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.

Chemotherapy

Almost all patients with stage III colon cancer should receive chemotherapy after surgery for 6 - 8 months. This is called adjuvant chemotherapy. The drug 5-fluorouracil can 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. 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.

Radiation

Radiation therapy is sometimes 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, treatments directed 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

Support Groups

You can ease the stress of illness by joining a colon cancer support group. Sharing with others who have common experiences and problems can help you not feel alone.

Expectations (prognosis)

In many cases, colon cancer is treatable when it is caught early.

How well you do depends on many things, especially the stage of the cancer. When treated at an early stage, many patientssurvive at least 5 years after diagnosis. This is called the 5-year survival rate.

If the colon cancer does not come back (recur) within 5 years, it is considered cured. Stage I, II, and III cancers are considered possibly curable. In most cases, stage IV cancer is not considered curable, although there are exceptions.

Complications

Blockage of the colon, causing bowel obstruction
Cancer returning in the colon
Cancer spreading to other organs or tissues (metastasis)
Development of a second primary colorectal cancer

Calling your health care provider

Call your health care provider if you have:

Black, tar-like stools
Blood during a bowel movement
Change in bowel habits
Unexplained weight loss

Prevention

The death rate for colon cancer has dropped in the last 15 years. This may be due to increased awareness and screening by colonoscopy.

Colon cancer can almost always be caught by colonoscopy in its earliest and most curable stages. Almost all men and women age 50 and older should have a colon cancer screening. Patients at higher risk may need earlier screening.

Colon cancer screening can often find polyps before they become cancerous. Removing these polyps may prevent colon cancer.

Changing your diet and lifestyle is important. Medical research suggests that low-fat and high-fiber diets may reduce your risk of colon cancer.

Some studies have reported that NSAIDs (aspirin, ibuprofen, naproxen, celecoxib) may help reduce the risk of colorectal cancer. But these medicines can increase your risk of bleeding and heart problems. Your health care provider can tell you more about the risks and benefits of the medicines and other ways that help prevent colorectal cancer.

References

Cunningham D, Atkin W, Lenz HJ, Lynch HT, Minsky B, Nordlinger B, et al. Colorectal cancer. Lancet. 2010;375:1030-1047.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Colon cancer. Version 2.2013. Available at http://www.nccn.org/professionals/physician_gls/pdf/colon.pdf. Accessed November 16, 2012.
Smith RA, Cokkinides V, Brawley OW. Cancer screening in the United States, 2012: a review of current American Cancer Society guidelines and current issues in cancer screening. CA Cancer J Clin. 2012;62:129-142.