In their systematic review of data about the possible association between use of oral contraceptives and the incidence of several forms of cancer, Gierisch and colleagues (1) systematically excluded studies published before 2000. Although those earlier studies likely represent the majority of evidence on the topic, the authors sought “to maximize the proportion of subjects who used oral contraceptive formulations similar to those on the market.” I believe it is reasonable to ask whether any association between hormonal contraception and cancer incidence differs by hormone type, dose, route of administration, etc., and analyses that sum up the data bearing on these questions (to the extent that they are available) would be a nice contribution. Unfortunately, as the authors acknowledge, “year of study publication” may be only weakly correlated with any particular feature of hormone exposure: no doubt many women included in the studies published after 1999 would have taken preparations that had been available a number of years earlier. In any case, rather than assuming that data from prior years would not be informative, both earlier-published and later-published data could be examined for possible differences in the presence and size of any associations found.
I suggest that most results obtained in epidemiologic studies have a “shelf life” of more than 13 years!
See the Response, p. 677
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