Fecal occult blood testing: where do we stand?

Colorectal cancer (CRC) is the third most common cancer and the third leading cause of cancer death in the United States. The incidence of new cases of CRC is estimated to be 103,170, and approximately 51,000 of these cases will die in 2012, despite the fact that both the incidence and mortality of this disease are declining. Most CRCs develop from preexisting adenomatous polyps that can develop progressive genetic abnormalities, resulting in dysplasia and eventually carcinoma during a period of years. Larger adenomas and those with high-grade dysplasia or villous changes (advanced adenomas) have a greater risk of progressing to colon cancer. This challenge is an opportunity to prevent CRC by finding and removing adenomatous polyps, particularly advanced adenomas. The current goals of screening for CRC include detecting cancer at an early, curable stage and preventing colon cancer by identifying and removing the benign, typically asymptomatic precursor lesions (adenomatous polyps). Screening tests for colon cancer can be divided into two types, stool-based tests and structural tests. Stool-based tests include fecal occult blood testing (FOBT) and fecal DNA testing, which primarily detect cancer, although they will also detect some advanced adenomas. Structural tests such as colonoscopy, virtual colonoscopy and flexible sigmoidoscopy can detect both cancers and adenomatous polyps. Colonoscopy remains the criterion standard for detecting and preventing CRC and has been shown to reduce both the mortality and incidence of colorectal carcinoma. FOBT also has been shown in randomized controlled trials to reduce mortality from colon cancer. In the Minnesota Colon Cancer Control Study, 46,551 participants were randomly assigned to FOBT using guaiacimpregnated slides or to a control group. Three samples were collected at home with repeat testing annually or every 2 years during this study. At 13 years, the mortality rate for CRC was reduced by 33% in the annually screened group versus the control group. A 5-year extension study of the Minnesota trial with 18 years of follow-up demonstrated a 20% decline in the incidence of CRC in the annually screened group as compared with the control group. This is a real, although modest decline, and the most plausible explanation is the identification and removal of adenomatous polyps. Although the primary goal of FOBT is identification of early colorectal carcinoma, an important secondary goal is to identify advanced adenomas whose removal will result in the prevention of CRC. FOBT at the time of a digital rectal examination (DRE) in a physician’s office is a common practice, although it is not appropriate for screening. The sensitivity of a single digital FOBT was only 4.9% in a prospective study of 2665 patients who subsequently underwent colonoscopy. In a survey of 1147 primary care physicians, 33% reported using only a single in-office stool sample for FOBT; another 52.9% reported using a combination of both in-office and at-home tests. In this issue of the Southern Medical Journal, Bechtold and colleagues undertake a meta-analysis of studies comparing DRE versus spontaneous passage of stool for FOBT. The use of DRE for FOBT resulted in the detection of significantly fewer advanced adenomas (47% fewer advanced adenomas detected with DRE). This finding has important implications because advanced adenomas are important precursors of CRC and failure to detect and remove them will result in a higher incidence of carcinoma in the population screened by DRE-based FOBT than in patients screened with at-home FOBT. Based on this evidence and previous studies indicating that DRE-based FOBT is an insensitive and suboptimal screening method, the practice of in-office, single-sample, DRE-based FOBT should be stopped because it has no role in CRC screening. So, where do we stand regarding FOBT? FOBT remains an important alternative for CRC screening in individuals at average risk for the disease, although screening colonoscopy is the preferred strategy in most patients. The advantages of the FOBT are its simplicity and relatively low cost. The disadvantages are the requirement for dietary restrictions, the need for multiple stool samples, and the need for annual testing. To be effective, FOBT must be conducted on multiple stool samples (three for guaiac-based tests) because single samples have low test sensitivity and they must be repeated on an annual basis. Acceptable FOBTs include a high-sensitivity guaiac FOBT (eg, Hemoccult Sensa, Beckman Coulter, Brea, CA) or Invited Commentary