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, carcinoid tumors, 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 can often lead 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 on many things, including 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)
CHEMOTHERAPY
Almost all patients with stage III colon cancer
should receive chemotherapy after surgery for approximately 6 - 8 months. This
is called adjuvant chemotherapy. 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. 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
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
[Via: PubMed Health]
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