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Colon cancer is cancer that starts in the large instestine (colon) or the rectum (end of the colon). Such cancer is sometimes referred to as "colorectal cancer." When cancer starts in the lining of an organ such as the large intestine, it is called a carcinoma.
Other types of colon cancer such as lymphoma, carcinoid tumors, melanoma, and sarcomas are rare. In this article, use of the term "colon cancer" refers to colon carcinoma and not the other, more rare types of colon cancer.
Causes, incidence, and risk factors
There are over 130,000 cases of colorectal cancer diagnosed in the United States each year, and over 50,000 deaths. Colorectal cancer is the second leading cause of cancer deaths. In almost all cases, however, this disease is entirely treatable if caught early by colonoscopy.
There is no single cause for colon cancer. However, almost all colon cancers begin as benign polyps which, over a period of many years, develop into cancers.
Factors that increase the risk of colon cancer are colorectal polyps, cancer elsewhere in the body, a family history of colon cancer, and ulcerative colitis.
Patients with a history of breast cancer have a slightly increased risk of developing colon cancer. Certain genetic syndromes increase the risk of developing colon cancer in affected families.
Dietary factors that have been associated with colon cancer are a high-meat, high-fat, low-fiber diet. However, some studies found that the risk is not reduced when people switch to a high-fiber diet, so the cause of the link is not yet clear.
With proper screening, colon cancer should be detected BEFORE the development of symptoms, when it is most curable.
Most cases of colon cancer have no symptoms. The following symptoms, however, may indicate colon cancer:
- Diarrhea, constipation, or other change in bowel habits that does not resolve
- Blood in the stool
- Unexplained anemia (anemia in any adult who is not a menstruating woman should almost always be evaluated by a colonoscopy)
- Abdominal pain and tenderness in the lower abdomen
- Intestinal obstruction
- Weight loss with no known reason
- Stools narrower than usual
Signs and tests
A physical examination rarely shows any abnormalities, although an abdominal mass may be present. A rectal examination may reveal a mass in patients with rectal cancer, but not colon cancer.
A colonoscopy or sigmoidoscopy may reveal evidence of cancer. However, only colonoscopy (NOT sigmoidoscopy) examines the entire colon.
A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, a possible indicator of colon cancer. However, this test is often negative in patients with colon cancer. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures, either colonoscopy or sigmoidoscopy. Finally, a positive FOBT doesn't necessarily mean the person has cancer -- "false positives" may be caused by some medications and other factors.
A blood count may reveal evidence of anemia with low iron levels. A CT scan may show an abdominal mass, although this test is not very good at detecting colon cancer.
Treatment depends partly on the stage of the cancer. This means how far the tumor has spread through the layers of the intestine, from the innermost lining to outside the intestinal wall and beyond:
Stage 0: Very early cancer on the innermost layer (more accurately considered a precursor to cancer)
Stage I: Tumor in the inner layers of the colon
Stage II: Tumor has spread through the muscle wall of the colon
Stage III: Tumor that has spread to the lymph nodes
Stage IV: Tumor that has spread to distant organs
Stage 0 colon cancer may be treated by cutting out the lesion, often via a colonoscopy. For stages I, II, and III cancer, more extensive surgery to remove a segment of colon containing the tumor and reattachment of the colon is necessary. (See colon resection.) This procedure only rarely requires a colostomy.
Almost all patients with stage III colon cancer, after surgery, should receive chemotherapy (adjuvant chemotherapy) with a drug known as 5-fluorouracil given for approximately 6 - 8 months. This drug has been shown to increase the chance of a cure. There is some debate as to whether patients with stage II colon cancer should receive chemotherapy after surgery, and patients should discuss this with their oncologist.
Chemotherapy is also used for patients with stage IV disease in order to shrink the tumor, lengthen life, and improve the patient's quality of life. Irinotecan, oxaloplatin, and 5-fluorouracil are the 3 most commonly used drugs, given either individually or in combination. There are oral chemotherapy drugs which are similar to 5-fluroruracil, the most commonly used being capecitabine (Xeloda).
Oxaliplatin, a newer chemotherapy drug, was approved by the FDA in 2002 and is also active against colon cancer. It is often used in combination with 5-fluorouracil, and studies are being done that combine it with other chemotherapy drugs. Other chemotherapy agents, including drugs that specifically target abnormalities in cancer cells, are currently in development and undergoing clinical trials.
For patients with stage IV disease that is localized to the liver, various treatments directed specifically at the liver can be used. Tumors may be surgically removed, burned, or frozen in some cases. Chemotherapy or radioactive substances can sometimes be infused directly into the liver.
Radiation therapy is occasionally used in patients with colon cancer, but this is often used in combination with chemotherapy for patients with stage III rectal cancer.
For additional resources and information, see colon cancer support group.
If the patient's colon cancer does not come back (recur) within 5 years, it is considered cured. This is because colon cancer rarely comes back after 5 years. Stage I, II, and III cancers are considered potentially curable. In most cases, stage IV cancer is not curable.
Stage I has a 90% 5-year survival. Stage II has a 75 - 85% 5-year survival, and Stage III a 40 - 60% 5-year survival. These numbers take into account that for stage III patients (and in some studies, stage II patients), chemotherapy improves the chance of 5-year survival.
Patients with stage IV disease rarely live beyond 5 years, and the median survival (meaning half the patients live longer, and half shorter) with treatment is between 1 and 2 years.
Cancer spreading to other organs or tissues (metastasis) Recurrence of carcinoma within the colon Development of a second primary colorectal cancer Calling your health care provider
Colon cancer is, in almost all cases, a treatable disease if caught early. Removal of premalignant polyps by colonoscopy essentially prevents colon cancer. Any man or woman age 50 or over who has not had a colonoscopy should call his or her physician to schedule one.
Additionally, call your physician if you develop blood in the stool (either visible blood or blood detected by a home fecal occult blood test), black tarry stool, or a change in bowel habits. However, it is important to emphasize that most people with colon cancer have no symptoms.
Approximately 50,000 people die of colon cancer every year. Yet, colon cancer can almost always be caught in its earliest and most curable stages by colonoscopy. Almost all men and women age 50 and older should have a colonoscopy.
Colonoscopy is almost always painless and most patients are asleep for the entire procedure. Taking laxatives and/or enemas before the test to clean out the colon isn't fun, but most people find this to be the worst part of the procedure. It may be embarrassing or awkward, but it is certainly better than having cancer.
Certain people may require colonoscopies before age 50. These include persons with a history of colon polyps or inflammatory bowel disease, and people with a first degree relative (mother, father, brother or sister) with colon cancer that developed before the age of 60.
Additionally, patients with personal or family history of other types of cancer may need to consider colon cancer screening at an earlier age.
Fecal occult blood test, sigmoidoscopy, and barium enema are other screening tests that can be used for early detection and prevention of colon cancer, but colonoscopy remains the gold standard.
A new test, a virtual colonoscopy, uses CT scan technology to visualize the colon. There are several problems with this test, however. First, it is early in development and we still don't have enough information to determine how accurate it really is. Second, patients must take a preparation the night before to clean out the colon. Finally, if an abnormality is seen, the patient must still undergo a traditional colonoscopy.
Dietary and lifestyle modifications are important. Some evidence suggests that low-fat and high-fiber diets may reduce your risk of colon cancer. However, even patients who follow strict diets can develop this disease and require colonoscopy.
Some evidence suggests that non-steroidal anti-inflammatory drugs (NSAIDs) may help prevent colon cancer, but again, screening is still necessary.
- Cancer.gov colorectal cancer
- Current clinical trials
- Complementary medical clinical trials
- Photos at: Atlas of Pathology
- Preventing Bowel Cancer Comprehensive information with patient stories - informedhealthonline.org
- Bowel Cancer UK (charity)
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