Prospective Analysis of Breastfeeding History and Ovarian Cancer Risk: Results From the Ovarian Cancer Cohort Consortium

Breastfeeding has been found to be associated with decreased ovarian cancer risk, but prospective analyses are sparse and limited by insufficient sample sizes to assess associations by histotype and patient characteristics. To investigate the association between breastfeeding (ever/never, duration, and timing) and incident epithelial ovarian cancer risk overall and by histotype, we leveraged harmonized individual-level data from 11 prospective cohort studies participating in the Ovarian Cancer Cohort Consortium, including 620,645 parous individuals, among whom 3730 developed incident epithelial ovarian cancer. Using pooled logistic regression models, odds ratios (ORs) and 95% CIs were calculated for the association between breastfeeding and ovarian cancer risk. Ever versus never breastfeeding was associated with a 15% lower risk of ovarian cancer (OR = 0.85, 95% CI = 0.75-0.96), with inverse associations observed for high-grade serous (OR = 0.89, 95% CI = 0.81-0.98) and endometrioid tumors (OR = 0.74, 95% CI = 0.58-0.95). Compared to never breastfeeding, inverse associations were observed for breastfeeding for more than 12 months across total pregnancies (OR = 0.79, 95% CI = 0.68-0.92) as well as for durations of 1-3 months (OR = 0.85, 95% CI = 0.74-0.98). Similar results were observed when stratified by parity. Although risk reduction persisted for up to 30 years since last breastfeeding (OR = 0.81, 95% CI = 0.72-0.91; p-trend < 0.0001), the inverse association was greatest for more recent breastfeeding (OR = 0.56, 95% CI = 0.47-0.66 for < = 20 years). This pooled prospective study provides further evidence that breastfeeding, even for less than 3 months, is associated with lower ovarian cancer risk overall and across most histotypes independent of parity.