Objective:
Non-steroidal anti-inflammatory drug (NSAID) use has been linked to a reduction in the risk of several cancer types. For endometrial cancer, however, results have been inconsistent. To summarize the available evidence on the risk of endometrial cancer associated with use of aspirin or non-aspirin (NA-) NSAIDs, we performed a systematic review and meta-analysis of observational studies.

Methods:
We conducted a bibliographic database search in PubMed, Embase and Cochrane Library. Relative risk estimates were extracted from eligible case–control and cohort studies and pooled using a random effects model.

Results:
Six case–control and seven cohort studies were found eligible for our meta-analysis. We observed risk reductions in endometrial cancer associated with regular use of aspirin (case–control: 11%, cohort: 8%) and NA-NSAIDs (case–control: 9%, cohort: 6%), compared to non-use. However, the pooled risk ratios were not statistically significant. Higher risk reductions were seen with high frequency of notably aspirin use (case–control: 37%, cohort: 20%). The inverse association between regular aspirin use and endometrial cancer risk was strongest among women with a body mass index above 30 (case–control: 44%, cohort: 20%).

Conclusions:
Regular use of aspirin or NA-NSAIDs was associated with a marginally reduced risk of endometrial cancer. Larger risk reductions were linked with high frequency of NSAID use and high BMI.