Reproductive factors, adiposity, breastfeeding and their associations with ovarian cancer in an Asian cohort.

Purpose: The aim of this study was to assess associations of breastfeeding, adiposity and reproductive risk factors with ovarian cancer risk in a Singaporean population. In addition to the main analysis, interaction effects of parity on other risk factors were examined.

Methods: A retrospective cohort consisting of 28,201 women with 107 incident ovarian cancers in up to 17 years of follow-up from the Singapore Breast Cancer Screening Project (1994-1997) was studied. Hazard ratios (HRs) for risk factors were estimated using Cox proportional hazards models.

Results: Body mass index and breastfeeding were found to have no statistical significant association with ovarian cancer risk. Gravidity was inversely associated with ovarian cancer risk [each pregnancy, adjusted HR 0.89, 95% confidence interval (CI) 0.81, 0.97], while results for parity were very similar (per delivery, HR 0.89, 95% CI 0.81, 0.98). Each additional year of ovulatory period was found to increase ovarian cancer risk by 2% (HR 1.02, 95% CI 1.00, 1.04). Each year increase in total duration of oral contraceptive use reduced ovarian cancer risk by 6% (HR 0.94, 95% CI 0.85, 1.02).

Conclusions: Parity, gravidity and shorter ovulatory period were associated with lower ovarian cancer risk. Breastfeeding and body mass index were not associated with ovarian cancer risk, while increased duration of oral contraceptive use resulted in borderline risk reduction. No significant evidence was found to suggest that parity had an interaction effect on any risk factor.