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FAQs - Fast Facts (Stool-Based DNA Test)

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Question: Should the stool-based DNA test be used as a screening test for colorectal cancer?

Answer: Because fewer than 50% of persons aged 50 years or older are screened for colorectal cancer, noninvasive, convenient, acceptable strategies for colorectal screening are emerging. Stool-based DNA (SB-DNA) testing is currently being compared with fecal occult blood testing (FOBT), the presently acceptable noninvasive test, and colonoscopy, the invasive gold standard. The differences between screening strategies are:

  • SB-DNA testing examines genetic abnormalities identified in colon cancer. This in vitro molecular biology technique analyzes the stool for mutations in the adenomatous polyposis coli (APC) gene.
  • FOBT detects only occult blood, which may be indicative of cancer in the colon.
  • Colonoscopy visualizes the presence of polyps that can be excised for biopsy.

The screening preferences of 4,042 average-risk individuals aged 50 years or older were reported in a prospective survey.1 The 25-item questionnaire was completed 48 hours after undergoing colonoscopy. The 3 screening tests were rated for preparation and test-related features. SB-DNA was preferred by 45% of respondents compared with 32% who preferred FOBT, and colonoscopy was preferred by 15% of respondents. However, colonoscopy was perceived as more accurate.

Imperiale and colleagues2 tested the sensitivity of the 2 screening measures in 4,404 individuals considered average risk and asymptomatic. The overall results were:

  • SB-DNA testing was 4 times more sensitive than FOBT for detecting invasive cancer and twice as sensitive for adenomas with high-grade dysplasia. If cancer is present, the sensitivity is greater.
  • The authors report that these findings reflect lower sensitivity compared with the results of previous studies but that they should be compared with results for which colonoscopy was the reference standard for all patients.

The cost of SB-DNA testing is currently between $400 and $800, compared with a range of $3 to $40 for FOBT.3 In terms of cost spent on testing to save one life, SB-DNA could be $47,700, whereas colonoscopy, considered twice as accurate in detecting CRC, costs only half as much per life saved. In another study, SB-DNA had a sensitivity of 91% for the detection of CRC and 82% for the identification of adenomas, supporting the results of other studies showing that its sensitivity is higher in patients with known CRC.4 Cigna Healthcare’s coverage position states that the “stool-based test is not intended to replace the colonoscopy in those patients who are willing to undergo the procedure” and “is not intended as a primary tool for individuals at increased risk.”5 Studies conclude that there may be a role for SB-DNA testing for individuals who may not be willing to undergo colonoscopy, which remains the “gold-standard” screening test. One-time testing is not reliable, and further studies are needed.

References

  1. Schroy PC, Heeren TC. Patient perceptions of stool-based DNA testing for colorectal cancer screening. Am J Prev Med. 2005;28:208-214.
  2. Imperiale TF, Ransohoff DF, Itzkowitz SH, et al. Fecal DNA versus fecal occult blood for colorectal-cancer screening in an average population. N Engl J Med. 2004;351:2704-2714.
  3. Woolf SH. A smarter strategy?—reflections on fecal DNA screening for colorectal cancer [editorial]. N Engl J Med. 2004;351:2755-2757.
  4. Ahlquist DA, Skoletsky JE, Boynton KA, et al. Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel. Gastroenterology. 2000;119:1219-1227.
  5. Cigna Healthcare coverage position. Available here. Accessed September 11, 2006.

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This page was last modified on 9/21/2006, at 1:45:49 pm ET.