• Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, 9609 Medical Center Drive, Rockville, MD 20850, USA. Electronic address: lauren.hurwitz@nih.gov.
• Division of Cancer Prevention, National Cancer Institute, National Institutes of Health, 9609 Medical Center Drive, Rockville, MD 20850, USA.
• Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, 9609 Medical Center Drive, Rockville, MD 20850, USA.

OBJECTIVE: Frequent use of aspirin has been associated with reduced ovarian cancer risk in observational studies, but it is unclear if only daily, low-dose aspirin confers a protective benefit. We examined associations between patterns of aspirin use and ovarian cancer risk among postmenopausal women in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial.

METHODS: Participants were enrolled in PLCO between 1993 and 2001 and followed for cancer outcomes through 2014. Detailed data on aspirin use (e.g., dose, frequency and duration) were ascertained via the supplemental questionnaire (SQX) administered in 2006-2007. We used Cox proportional hazards regression to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for associations between aspirin use (defined as use ≥once/week) and incident ovarian cancer. We conducted analyses among all women in the study sample and stratified by age at the time of the SQX.

RESULTS: There were 41,633 women included in this analysis, of whom 223 developed incident ovarian cancer. Overall, aspirin use was not significantly associated with ovarian cancer risk (HR: 0.93, 95% CI: 0.72-1.21). Among women <70 years, there was suggestion of an inverse association for daily use of aspirin (HR: 0.65, 95% CI: 0.40-1.05), low-dose aspirin (HR: 0.79, 95% CI: 0.51-1.24) and daily use of low-dose aspirin (HR: 0.64, 95% CI: 0.38-1.09).

CONCLUSIONS: These findings suggest a potential modest effect of daily, low-dose aspirin in reducing ovarian cancer risk. However, effect estimates were imprecise given the small number of events, and further research will be needed to confirm and extend these findings.