One retrospective cohort study conducted by Kwon and colleagues disclosed that regular use of aspirin (≧two times of use every 1 week) correlated with a decreased risk of gastric cancer as compared with nonregular use of aspirin in women (adjusted HR = 0.52 and 95% confidence interval = 0.37–0.73; ref. 1). Some points not shown in the original article are discussed.

First, based on Table 2 in Kwon and colleagues study, we estimated that the incidence rates of gastric cancer were about 4 every 100,000 person-years (or 51/1,258,158 person-years) in women with regular use of aspirin and 6 every 100,000 person-years (or 125/2,097,414 person-years) in women with nonregular use of aspirin. These results indicated the relative risk of gastric cancer was 0.67 for regular use versus nonregular use of aspirin, but the absolute risk reduction was about 0.00002. If we only see the relative risk, the protective effect of...

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