Background: Chronic inflammation may play an etiologic role in ovarian and endometrial cancer, and it is hypothesized that nonsteroidal anti-inflammatory drugs (NSAID) decrease the risk of developing these malignancies. No prospective study with a large multiethnic population has explored this hypothesis.

Methods: We investigated whether NSAID use was associated with risks of ovarian and endometrial cancer in the Multiethnic Cohort Study. Medication use of at least twice a week for ≥1 month was assessed at baseline. Multivariable relative risks (RR) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models.

Results: During 13.3 years of follow-up, 275 ovarian and 620 endometrial incident cases were identified among approximately 64,000 women included in this analysis (16.5% African Americans, 30.8% Japanese, 7.7% Native Hawaiians, 18.9%, Latinas, and 26.0% whites). The RR (95% CI) for ovarian cancer associated with aspirin, non-aspirin NSAIDs, and acetaminophen were 0.87 (0.68–1.14), 0.97 (0.74–1.26), and 0.86 (0.67–1.12), respectively. The RR (95% CI) for endometrial cancer associated with aspirin, non-aspirin NSAIDs, and acetaminophen were 0.93 (0.79–1.10), 0.88 (0.74–1.05), and 0.96 (0.81–1.13), respectively. No heterogeneity across ethnic groups (P ≥ 0.29) or dose–response relation with increased duration of use (P_trend ≥ 0.16) was observed. The results did not differ by tumor histology.

Conclusions: We found no compelling evidence to support an association between the use of NSAIDs and risk of ovarian and endometrial cancers in a multiethnic population.

Impact: It is unlikely that NSAID is involved in the etiology of endometrial and ovarian cancer. Cancer Epidemiol Biomarkers Prev; 21(9); 1441–9. ©2012 AACR.