Combined oral contraceptive use before the first birth and epithelial ovarian cancer risk

BACKGROUND: Combined oral contraceptive (COC) use reduces epithelial ovarian cancer (EOC) risk. However little is known about risk with COC use before the first full-term pregnancy (FFTP). METHODS: This Canadian population-based case-control study (2001-2012) included 854 invasive cases/2139 controls aged 40 years who were parous and had information on COC use. We estimated odds ratios (aORs) and 95% confidence intervals (CI) adjusted for study site age parity breastfeeding age at FFTP familial breast/ovarian cancer tubal ligation and body mass. RESULTS: Among parous women per year of COC use exclusively before the FFTP was associated with a 9% risk reduction (95% CI=0.86-0.96). Results were similar for high-grade serous and endometrioid/clear cell EOC. In contrast per year of use exclusively after the FFTP was not associated with risk (aOR=0.98 95% CI=0.95-1.02). CONCLUSIONS: Combined oral contraceptive use before the FFTP may provide a risk reduction that remains for many years informing possible prevention strategies.British Journal of Cancer advance online publication 13 December 2016; doi:10.1038/bjc.2016.400 www.bjcancer.com.