In their rebuttal of Kenneth Marshall's arguments against fecal occult blood screening for colon cancer,1 Sidney Winawer and Ann Zauber accuse Marshall of using “misleading data, unfounded assumptions and exaggerations to support his bias against screening.”2 It seems to us, however, that in their main article supporting the use of fecal occult blood screening for colorectal cancer,3 it is Winawer and Zauber who use misleading data, unfounded assumptions and exaggerations to bolster their bias in favour of such screening.
For example, Winawer and Zauber state that screening “was associated with the largest reduction in mortality (by 33%)”.3 We agree with Marshall4 that it is the absolute reduction — the actual number of people who benefit — that counts, not the relative reduction rate that Winawer and Zauber quote. If disease Y caused 3 deaths per year in Canada and it was proven that some sort of expensive and potentially harmful screening program could reduce this rate to 2 deaths per year, would Winawer and Zauber advocate adoption of this program? After all, the program would achieve a 33; reduction in mortality, although only 1 life would be saved.
With almost 50 years of combined experience in a rural family practice setting, we share Marshall's concerns4 that results obtained in tertiary care hospitals may not necessarily be extrapolated to the primary care setting, where the staff may have less expertise, motivation and experience than the staff in tertiary care settings.
We are concerned that the current state of technology — a fecal occult blood screen of low predictive value, followed by an invasive test — is not sufficiently mature for a full-blown societal commitment to a massive screening program.
References
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