Objective: to examine the association between breastfeeding patterns and risk of epithelial ovarian cancer.

Methods: We examined duration, age, and timing factors related to breastfeeding episodes among parous women in a population-based case-control study conducted in western PA, eastern OH, and southwestern NY from 2003-2008 (the HOPE Study). We compared 689 incident cases of epithelial ovarian cancer (EOC) to 1572 community controls frequency-matched to cases by age and three-digit telephone exchange. Multivariable unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for EOC associated with breastfeeding patterns adjusting for age, race, parity, duration of oral contraceptive use, education, tubal ligation, hysterectomy, talc use, and family history of breast or ovarian cancer.

Results: Compared to never breastfeeding, breastfeeding any offspring was associated with a significant 28% reduction in EOC risk (OR=0.72; 95% CI=0.58-0.90). That protection appeared to last more than 30 years (OR=0.70, 95%CI=0.54-0.92), although the magnitude of the protection decreased over time (OR=0.54, 0.74, 0.83 and 0.70 for <10, 10-19, 20-19, and 30+ years since last breastfeeding episode, trend p=0.013). Greater number of offspring nursed provided increased protection (OR=0.75, 95%CI=0.60-0.93 and OR=0.44, 95%CI=0.28-0.63 for nursing 1-2 and 3+ offspring, respectively, compared to never breastfed, trend p<0.001). Longer total breastfeeding duration also provided increased protection (OR=0.74 and 0.58 for less than and greater than 1 year total duration, respectively, compared to never breastfed, trend p=0.002). Although there did not appear to be any benefit from longer average duration per episode (OR=0.73 and OR=0.70 for 1-3 and 4 or more months average per episode, respectively), longer duration for both the first (OR=0.75 and OR=0.67 for 1-3 and 4 or more months, respectively, trend p=0.004) and last (OR=0.76 and OR=0.65 for 1-3 and 4 or more months, respectively, trend p=0.003) breastfeeding episode provided greater protection. Earlier age at first breastfeeding episode appeared more protective than a later age of first breastfeeding (OR=0.65, 0.73,0.94, for first episode at age <25, 25-29, and 30+, respectively). Age at last breastfeeding episode did not appear to have a substantial impact on risk (OR=0.67, 0.78, 0.74, for last episode at age <25, 25-29, and 30+, respectively).

Conclusions: Breastfeeding is protective against EOC. Although this protection decreases over time, it persists for more than 30 years. Longer total duration and increasing number of offspring nursed increase the protective effect, as does an earlier age at first breastfeeding episode.

Impact: Interventions to encourage and support women in breastfeeding can reduce EOC risk.

This abstract is also being presented as Poster B18.

Citation Format: Danielle Wallack, Clareann H. Bunker, Robert P. Edwards, Joseph L. Kelley, Kunle Odunsi, Kirsten Moysich, Roberta B. Ness, Maria Mori Brooks, Francesmary Modugno. Breastfeeding protects against epithelial ovarian cancer: Results of the HOPE Study. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr PR10.