With screening and treatment methods now available, most colon cancer deaths could be prevented.
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Colon cancer kills nearly 50,000 Americans every year, more than any other cancer except lung cancer. With screening and treatment methods now available, most of these deaths could be prevented.
Cancers of the colon usually begin as benign growths known as polyps deep within the bowels that develop slowly over a number of years into invasive tumors. With regular screening and removal of polyps when they are found, it’s estimated that the incidence of colon cancer could be reduced by at least 80 percent.
Symptoms of cancer include a change in bowel habits, blood in the stool and unexplained anemia or weight loss, but in the majority of cases, there are no noticeable signs until the cancer has advanced too far to be treated effectively. That’s why screening is so important. The American Cancer Society and the U.S. Preventive Services Task Force recommend screening of all Americans starting at age 50 and earlier for persons with higher-than-average risk. Anyone with a first degree relative diagnosed with colon cancer is at high risk; so are persons who have been treated for cancer or who have bowel diseases such as ulcerative colitis.
Among the variety of screening options available, most medical groups recommend a combination of yearly fecal occult blood testing (FOBT) plus periodic examination of the colon through use of a scope or thin lighted tube that is inserted into the bowel through the anus. Examination can also be performed through a double contrast barium enema.
Fecal occult blood testing has the advantage of being inexpensive and non-invasive. It requires that the patient collect a series of stool samples which are then examined in the laboratory for the existence of blood that can be seen only with a microscope.
Blood in the stool may indicate a bleeding polyp, but false positives can occur because the patient has hemorrhoids or has eaten red meat or other foods prior to testing. Unfortunately, bleeding is more likely to occur relatively late in cancer development so some early cancers go undetected with FOBT alone.
Regular Screening Saves Lives
According to results of a 1993 study, yearly FOBT resulted in a 33.4 percent reduction in colon cancer deaths, although some of these were attributed to good fortune–the discovery of a non-bleeding cancer through colonoscopy as a consequence of a false positive result. Testing every other year also reduced mortality, but to a lesser degree.
Sigmoidoscopy, which allows examination of the lower third of the colon, costs about $150 and can be performed with only minor discomfort in the doctor’s office. According to one study, the combination of FOBT and sigmoidoscopy detected 76 percent of early cancers.
Colonoscopy is not only more sensitive but allows the doctor to visualize the entire colon and remove any polyps that might be found. It is considered the gold standard screening method but is more invasive, costs about $800 and requires anesthesia.
A typical recommendation is FOBT once a year plus sigmoidoscopy every five years or colonoscopy every 10 years.
Two promising new options may soon make colon cancer screening more widely accepted.
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Most patients describe these procedures as uncomfortable rather than painful; nevertheless, there is considerable reluctance to have them performed. A Centers for Disease Control telephone survey found that only 44 percent of Americans age 50 or over had been screened with FOBT within the past year or with flexible sigmoidoscopy or colonoscopy within the past five years.
Two promising new methods offer the hope that screening may soon become more widely accepted.
Recent studies indicate that aspirin and NSAIDs may prevent recurrence of polyps and cancer.
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Virtual colonoscopy uses a computerized tomography (CT) scan to examine the colon without the use of a scope–and the accompanying risk. However, like sigmoidoscopy and colonoscopy, this procedure requires that the patient empty the bowels through food restriction, laxatives and enemas–a requirement that turns many persons away.
An even less invasive method involves laboratory testing of a stool sample to detect changes in DNA. Early studies of the test found a 91 percent sensitivity for cancer.
If a polyp or early cancer is found, colonoscopy can be used to remove the lesion without cutting through the abdominal wall. The patient may then require more frequent screening and monitoring.
In another important development, recent studies indicate that aspirin and nonsteroidal antiinflammatory drugs (NSAIDs), including COX-2 inhibitors, may prevent recurrence of polyps or cancer in such individuals as well as in persons with a genetic risk for colon cancer.
Calcium supplements have also been found effective in reducing the rate of recurrence. Even though observational studies indicate that persons eating a high-fiber diet are less likely to die of colon cancer, studies have failed to find increased fiber in the diet to be effective in preventing recurrence of polyps or cancer.
For larger cancers, unfortunately, the doctor may need to remove part of the bowel plus the lymph nodes near the colon for laboratory examination to tell if the cancer has spread.
In some cases, the healthy ends of the bowel can be stitched back together, but if too much has been removed, a colostomy may be necessary. A stoma (or opening) is made on the outside of the body for waste to pass through and be collected in a bag.
Depending on how far the cancer has spread, chemotherapy and radiation therapy may also be necessary following surgery. Even for the most advanced cancers, one study found that chemotherapy significantly improved survival time and quality of life–even considering the often-severe side effects.
A new treatment medication, irinotecan (Camptostar), was introduced in 1998–the first drug to get full approval for metastatic colorectal cancer in 40 years. Approval of oxaliplatin followed in 2002. Used as an addition to standard therapy of fluorouracil and leucovorin, both new treatments have been shown to result in greater tumor shrinkage and a delay in cancer growth for patients who had not responded well to standard therapy.
Experimental drugs that disrupt the tumor’s supply of nutrients by inhibiting the growth of new blood vessels (angiogenesis) have also been found effective and offer hope for significant progress in the future, even against the most advanced cancers. These are also used in combination with standard chemotherapy.
Other promising approaches include immunotherapy, using the body’s immune system to target cancer cells, and gene therapy, usually involving correction of a gene defect.
New treatments–those already in use and those waiting in the wings–have the potential to dramatically improve survival time. But the most effective approach against colon cancer is much simpler: screening, prevention and early detection.
REFERENCES:
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G.A. Chung-Faye and D.J. Kerr, “Innovative Treatment for Colon Cancer,” British Medical Journal, December 2, 2000.
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Colin McArdle, “Primary Treatment–Does the Surgeon Matter?” British Medical Journal, November 4, 2000.
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N. Seppa, “Treatment Combinations Stall Colorectal Cancer,” Science News, June 7, 2003.
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