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Cancer Resources

Colonoscopy Screening
12/15/09

The colon and rectum are parts of the body that most people prefer not to think about, certainly not discuss and absolutely not submit to invasion. However, it is precisely these attitudes that must be overcome for the second leading cause of cancer death in the United States, colorectal cancer, to be effectively prevented. 

More than 130,000 Americans will be diagnosed with colorectal cancer this year and, tragically, 56,000 patients will succumb to the disease. The incidence in males and females is approximately equal and 10% of those diagnosed will be under the age of 50. Most frustrating to patients and physicians the fact that 90% of cases of colorectal cancer could have been either prevented or diagnosed at a curable stage with proper screening. The scientific rationale for preventing colon cancer is that nearly all colon cancers emerge from polyps, benign mushroom-like growths on the lining of the colon. For cancer to develop, the normal tissue must sustain several genetic alterations that take tissue through various stages of polyp growth until ultimately reaching the stage of malignancy, a process that may take 10 to 15 years. 

Much research has been aimed at behavioral modifications that may discourage progression within the polyp-cancer sequence. Some studies suggest a low fat, high fiber diet is beneficial. Calcium, selenium, vitamin E and folate may also reduce risk. Studies have shown that regular use of aspirin decreases the risk of colon cancer. Recently, celecoxib, a non-steroidal anti-inflammatory drug of the new selective cox-2 inhibitor class, has been approved to prevent progression of polyps in patients with familial adenomatous polyposis, a rare genetic disorder associated with the highest risk of colon cancer.  Unfortunately, none of these lifestyle changes or medications can be considered reliable in preventing colon cancer.

The mainstay of prevention has been screening, examination of persons at risk in order to detect pre-malignant lesions or curable early cancers. Traditionally, screening has involved examination of stool for trace blood (fecal occult blood testing) yearly after age 50, rectal examination by insertion of a gloved finger (digital rectal examination) yearly after age 40, and visualization of the lower part of the colon (flexible sigmoidoscopy) every 3 to 5 years after age 50. 

Colonoscopy, or full examination of the colon by passing a flexible tube with a video camera on its tip through the entire colon, was reserved in the past for patients with a positive screening test or with a risk factor for colon cancer. Such risk factors include a family history or personal history of premalignant (adenomatous) colon polyps or colon cancer, a history of colitis (ulcerative colitis or Crohn's colitis) of greater than 8 years duration, or a genetic syndrome associated with colon cancer.  Perhaps of greatest concern is that less than 30% of persons deemed appropriate for screening are actually screened, underscoring the need to intensify education of the public as well as primary care physicians.

Only colonoscopy provides highly accurate diagnosis as well as the opportunity to remove polyps or biopsy cancer. The procedure of colonoscopy begins with preparation on the day prior to the procedure with a laxative solution to cleanse the colon.  Immediately prior to the procedure patients are generally sedated with intravenous medication.  Colonoscopy itself takes approximately 20 minutes and involves little or no discomfort to the patient.  Significant complications occur in under 0.5% of patients.

Two recent studies involving over 5,000 colonoscopies have shown that over 50% of advanced polyps or cancers were found in patients with no lesions within the reach of sigmoidoscopy. These patients, if screened with sigmoidoscopy alone, would have been falsely reassured. Based on this data, the argument has been made that relying on sigmoidoscopy for colon screening is the logical equivalent of performing mammography on only one breast. Colonoscopy in all persons regardless of risk factors at age 50 is now considered the most effective strategy in preventing colon cancer. Adopting this strategy on a national level would be expected to save 30,000 lives annually.

In the future, it is anticipated that screening for colon cancer will be even less invasive. Virtual colonoscopy, a computer generated reconstruction of the colon based on a high-speed CT scan, has shown promising results as a modality that may be used to select persons in the general population needing colonoscopy. Early trials with an ingestible capsule containing a video chip that could be controlled by remote provide a glimpse into the future of colon screening. Nevertheless, for today, the standard of care is colonoscopy for all persons at age 50 and earlier for high-risk individuals.

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