Aspirin and the risk of nondigestive tract cancers: An updated meta‐analysis to 2019

Aspirin has been associated with a reduced risk of colorectal and other selected digestive tract cancers, but the evidence for other neoplasms is still controversial. To provide an up-to-date quantification of the role of aspirin on lung, breast, endometrium, ovary, prostate, bladder, and kidney cancer, we conducted a systematic review and meta-analysis of all observational studies published up to March 2019. We estimated pooled relative risk (RR) of cancer or cancer death for regular aspirin use vs non-use by using random-effects models, and, whenever possible, we investigated dose- and duration-risk relations. A total of 148 studies were considered. Regular aspirin use was associated to a reduced risk of lung (RR = 0.88, 95% confidence interval [CI] = 0.79-0.98), breast (RR = 0.90, 95% CI = 0.85-0.95), endometrial (RR = 0.91, 95% CI = 0.84-0.98), ovarian (RR = 0.91, 95% CI = 0.85-0.97) and prostate (RR = 0.93, 95% CI = 0.89-0.96) cancer. However, for most neoplasms, nonsignificant risk reductions were reported in cohort and nested case-control studies and there was between-study heterogeneity. No association was reported for bladder and kidney cancer. No duration-risk relations were observed for most neoplasms, except for an inverse duration-risk relation for prostate cancer. The present meta-analysis confirms the absence of appreciable effect of regular aspirin use on cancers of the bladder and kidney and quantifies small and heterogeneous inverse associations for other cancers considered.