We appreciate Lai and colleagues’ interest in our study in which we reported associations between aspirin use and gastric adenocarcinoma in two large prospective cohort studies of U.S. men and women (1). Lai and colleagues calculated that comparing aspirin users with nonusers, the absolute rate difference was 2/100,000 person-years with a number-needed-to-treat (NNT) of 50,000 in women. Perhaps a more clinically interpretable metric of absolute risk would be based on persons at risk rather than person-years using an estimate calculated according to the mean follow-up time (30.6 years) of cohort participants. We would then estimate the risk of gastric cancer was 0.0018 [125 cases/(2,097,414 person-years/30.6 years)] among nonregular aspirin users, and 0.0012 [51 cases/(1,258,158 person-years/30.6 years)] among regular users. This translates to an NNT of 1,714, suggesting one case of gastric cancer could potentially be prevented by treating 1,714 women with aspirin regularly. Nonetheless, we concur that public...

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