Global Hospital & Healthcare Management

Dr. Otto Lin is a Member of the Digestive Diseases Institute at Virginia Mason Medical Center and Clinical Assistant Professor of Medicine at the University of Washington School of Medicine. After graduating from Harvard Medical School in 1994, he underwent subspecialty training in Gastroenterology at Stanford Hospital. He also holds a Master of Science degree in Health Services Research from Stanford University. He is active in clinical and outcomes research, having published numerous papers on a variety of topics, in particular colon cancer screening and surveillance.

 

The concept of colon cancer screening is based on the premise that it is a common, lethal and preventable disease. As of 2003, approximately 147,500 new cases of colorectal cancer were diagnosed annually in the U.S., translating to a cumulative lifetime risk of around 6%. Since the incidence of colon cancer increases with age, more than 90% of cases occur in people over 50. As the second leading cause of cancer death in the U.S., colon cancer is directly responsible for 57,100 deaths every year. In fact, almost 50% of patients diagnosed with colon cancer will eventually die from it.

 

Colon cancer is preventable because most cases develop from precancerous polyps known as “adenomas.” Large studies have demonstrated that removal of adenomas leads to a subsequent reduction in the incidence of colon cancer. Furthermore, colon cancer diagnosed and treated at earlier stages are associated with much better prognosis and survival. Therefore, the overall death rate from colon cancer may be reduced by screening measures designed to detect asymptomatic adenomatous polyps or early stage cancers.

 

In the U.S., there has been considerable interest in colon cancer screening in the average-risk population. These are people with no family history of colon cancer or polyps, no previous personal history of colon cancer or polyps and no history of inflammatory bowel disease. As shown in Table 1, recently published guidelines from the U.S. Multi-Society Task Force on Colorectal Cancer advocate screening all average-risk individuals age 50 and above using one of several approaches – high sensitivity fecal occult blood testing (FOBT) every year, flexible sigmoidoscopy every 5 years, double contrast barium enema every 5 years, computerized tomographic colonography (CTC), popularly known as “virtual colonoscopy” every 5 years, conventional colonoscopy every 10 years, or stool DNA testing at unspecified intervals.

 

Table 1. Screening guidelines (2008), by the U.S. Multi-Society Task Force on Colorectal Cancer. Screening is to start at age 50 for average-risk individuals.

 

Screening for colon cancer using FOBT is based on the observation that more than 60% of colon cancers bleed at some point over the course of one week. Usually, a set of 3 cards, each containing 2 separate windows, are used for samples. It is inappropriate to use stool obtained from a digital rectal examination for screening. Most studies report sensitivity rates of 30 to 60% and specificity rates of 90 to 95% for colon cancer and polyp detection. Several large, well-designed studies have reported reduced colon cancer mortality as a result of FOBT screening compared with no screening.  Newer forms of FOBT, including “high sensitivity” guaiac tests and immunochemical tests, may provide better accuracy. Flexible sigmoidoscopy is commonly performed by gastroenterologists, primary care physicians and other health care practitioners for colon cancer screening purposes. The discovery of an adenoma on sigmoidoscopy should prompt full colonoscopy. Several studies have shown convincingly that screening sigmoidoscopy is associated with a reduction of colon cancer mortality. Due to the limited reach of the sigmoidoscope, some cancers in the right colon may be missed. There is only limited data on the effectiveness of barium enema as a screening method. Direct comparisons of barium enema versus colonoscopy have shown that the latter is significantly more accurate for the detection of polyps and cancer. At present, barium enema is mainly used as a second-line modality only when the patient is not an appropriate colonoscopy candidate.

 

CTC uses data generated from multi-slice rapid computerized tomography to offer 2- and 3-dimensional reconstruction of the surface of the colon. Current protocols involve bowel cleansing and insertion of a rectal tube to distend the colon with air. Recent studies have reported accuracy values for CTC almost as high as that for conventional colonoscopy. Although endorsed by current guidelines, CTC is not reimbursed by Medicare or other private insurers for screening purposes, but is covered for patients who have had an incomplete colonoscopy. Disadvantages of CTC include radiation exposure, the need for bowel cleansing, and the inability to remove or sample potential polyps. Stool DNA testing is an emerging technique to detect characteristic DNA abnormalities in stool samples that identify patients likely to have colon cancer or large polyps. It is thought to be more accurate than traditional fecal occult blood testing but is much more expensive. It is endorsed by screening guidelines, but there is not enough data available to define the appropriate screening intervals. Finally, colonoscopy is generally accepted as the most accurate test for detecting colon polyps and cancer, although there is a small miss rate. It is also the only means by which adenomatous polyps can be removed. Therefore, follow-up colonoscopy is required when a positive result for all the other screening methods is encountered. The American College of Gastroenterology endorses colonoscopy as the “preferred” colon cancer screening test.

 

Individuals with a first-degree relative (i.e. parent, sibling or child) who developed colon cancer at age 60 or greater have a higher risk for developing colon cancer compared with average-risk individuals. It is generally recommended that these people be subjected to the same screening protocol as average-risk persons, except that the screening process should begin at age 40. People with a "strong" family history of colon cancer (i.e. multiple relatives with colon cancer or a single first degree relative who developed colon cancer before age 60) have a four-fold increased risk. Screening for this group should begin at age 40 or 10 years earlier than the age of diagnosis of the youngest affected relative, whichever is younger. Colonoscopy every 3 to 5 years is generally recommended. Patients with certain genetic conditions, such as familial adenomatous polyposis and hereditary non-polyposis colorectal cancer syndrome, or chronic inflammatory bowel disease involving the colon, have an extremely high risk of developing colon cancer. These patients require intensive screening and should be managed by a gastrointestinal specialist.

 

Almost all insurance plans will cover colon screening using sigmoidoscopy and FOBT. Most private insurance plans will also cover screening colonoscopy. Medicare pays for screening with annual FOBT, sigmoidoscopy every 4 years, or colonoscopy every 10 years. More frequent colonoscopy (every 1 to 2 years) is covered for high-risk patients.

 

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