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Authors Response to Letter to the Editor
Submit responseDear Editor,
We agree that a most interesting finding from our analysis (1) for the U.S. Preventive Services Task Force (USPSTF) is that all the screening strategies now recommended by the USPSTF are nearly equivalent for life years gained with screening when all have equivalent 100% adherence. We note that the USPSTF recommendation for the strategies of high sensitive guaiac or immunochemical fecal occult blood tests (FOBT) annually, flexible sigmoidoscopy every 5 years with a sensitive FOBT, and colonoscopy every 10 years are based on the perspective of a program of screening from ages 50 to 75 with the endpoint of life years gained rather than for screening at a point in time with the endpoint of reducing colorectal cancer incidence (2).
We also agree that the issue of adherence is a crucial component to the effectiveness of a screening intervention. The assumption of 100 percent adherence to all aspects of screening was used to provide a comparable assessment of potential efficacy for the different screening strategies and represents the best screening offer for those who adhere to testing, follow-up of positive findings, surveillance, and treatment. However, in clinical practice, adherence is very complex (considerably less than 100%) with variation by screening test (3) and repeat screening. As shown in Figure 3 of our paper (1), differential adherence does influence the effectiveness of the intervention. We noted “in practice adherence is critical and the ultimately the best option for a patient is the one that he or she will attend”. We agree that an important question to ask is what levels of relative adherence for colonoscopy and another screening test provide comparable levels of life years gained per number of colonoscopies. We agree that we do need randomized controlled trials to compare adherence and clinical outcomes after an invitation to participate in a colorectal cancer screening program using sensitive FOBT or colonoscopy.
References.
1. Zauber AG, Lansdorp-Vogelaar I, Knudsen AB, Wilschut J, van Ballegooijen M, Kuntz KM. Evaluating test strategies for colorectal cancer screening: a decision analysis for the U.S. Preventive Services Task Force. Ann Intern Med 2008:149:659-669.
2. Levin B, Lieberman DA, McFarland B, et al. Screening and surveillance for early detection of colorectal cancer and adenomatous polyps 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA Cancer J Clin 2008; 58:130-160 and Gastroenterology 2008;134:1570-1595.
3. Shapiro J, Seeff LC, Thompson TD, Nadel MR, Klabunde CN, Vernon SW. Colorectal cancer test use from the 2005 National Health Interview Survey. Cancer Epidemiol Biomarkers Prev 2008;17:1623-30.
Conflict of Interest:
None declared
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Test-specific adherence may predict the best colorectal cancer screening strategy
Submit responseDear Editor,
The demonstration that all screening strategies recommended by the U.S. Preventive Services Task Force are nearly equivalent for prevention of colorectal cancer mortality (assuming 100% adherence) is the most interesting aspect of Zauber and colleagues’ analysis(1, 2). Differences in life-years gained between strategies for the MISCAN model ranged from 227 to 230 life-years gained/1000 persons, a range which is likely to be within the range of statistical error and/or small changes in model assumptions. In contrast, the differences in number of screening tests, and volume of associated colonoscopy required between strategies differed widely, by as many as 7637 tests/1000persons and 786 colonoscopies/1000 persons, respectively. These results raise a very important question: Are the relative expected life year gains associated with a colonoscopy only strategy enough to justify the movement in the U.S. towards favoring a more resource intense and invasive “structural” examination-based approach to screening(3)?
Prior to answering this question, we must consider whether rates of adherence to screening are test-specific, such that differences in adherence may be more important for prediction of the best screening strategy than test-specific sensitivity for neoplasia. This issue can be appreciated by examining Figure 3, where it is clear that 80% adherence to Hemoccult SENSA (HS) provides better outcomes per 1000 persons than 50% adherence to colonoscopy(2). Provision of more detailed analyses of outcomes relative to test-specific variation in adherence is desirable. For example, at what point of relative adherence does a more sensitive colonoscopy strategy dominate a less sensitive fecal immunochemical test (FIT) strategy? More importantly, if small (even in the range of 10%) advantages in adherence for the less sensitive strategies are associated with better projected outcomes relative to colonoscopy, then trials that compare both adherence and clinical outcomes after invitation to FIT or HS versus colonoscopy are warranted.
1. Screening for Colorectal Cancer: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2008.
2. Zauber AG, Lansdorp-Vogelaar I, Knudsen AB, Wilschut J, van Ballegooijen M, Kuntz KM. Evaluating Test Strategies for Colorectal Cancer Screening: A Decision Analysis for the U.S. Preventive Services Task Force. Ann Intern Med. 2008.
3. Levin B, Lieberman DA, McFarland B, et al. Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous Polyps, 2008: A Joint Guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA Cancer J Clin. 2008.
Conflict of Interest:
None declared