Abstract 640: Breastfeeding pattern and ovarian cancer risk: Results from the Ovarian Cancer Association Consortium
Authors: Sasamoto Naoko , Babic Ana , Jordan Susan , Risch Harvey , Harris Holly , Rossing Mary Anne , Doherty Jennifer , Goodman Marc , Thompson Pamela , Kjær Susanne K. , Jensen Allan , Schildkraut Joellen , Titus Linda , Cramer Daniel , Bandera Elisa , Sieh Weiva , McGuire Valerie , Sutphen Rebecca , Pearce Celeste L. , Wu Anna H. , Pike Malcolm , Webb Penelope , Modugno Francesmary , Terry Kathryn 
Published: August 2019

Abstract
Background: Ovarian cancer is the fifth leading cause of cancer deaths in US women with few modifiable risk factors. Breastfeeding has been observed to be associated with reduced risk of ovarian cancer in multiple studies. However, prior studies reporting the association between breastfeeding pattern and ovarian cancer risk by histologic subtypes have reported inconsistent findings, likely due to small sample size and lack of details on breastfeeding patterns. The objective of this study is to evaluate the association between breastfeeding patterns and ovarian cancer risk by histologic subtypes using individual questionnaire data from the Ovarian Cancer Association Consortium (OCAC).
Method: We evaluated breastfeeding patterns in relation to invasive ovarian cancer risk in 9,807 cases and 12, 971 controls from 13 studies in the OCAC. We performed pooled unconditional logistic regression to evaluate the association between breastfeeding and ovarian cancer risk and used multinomial logistic regression to evaluate the association by histologic subtype. We restricted the analysis to parous women and adjusted for study site, age, body mass index, race, education, oral contraceptive use, number of full-term births, family history of ovarian cancer, and birth decade (to account for change in breastfeeding practice over time). We additionally adjusted for age at first and last births simultaneously when examining the association between first and last age at breastfeeding and ovarian cancer risk.
Results: Women who reported ever breastfeeding had a 24% decreased risk of overall invasive ovarian cancer compared to women who never breastfed (OR=0.76, 95%CI: 0.71-0.81) and this association did not differ significantly by histologic subtypes (p-heterogeneity=0.09). Considering only episodes when women breastfed, we observed lower risk of ovarian cancer in women who had longer average duration per episode compared to women who breastfed &lt; 6 months on average per episode (OR=0.85, 95%CI: 0.77-0.93 for 6-12 months; OR=0.77, 95%CI: 0.66-0.89 for &gt; 12 months; p-trend &lt;0.0001). Older age at first and last breastfeeding was significantly associated with lower risk of ovarian cancer compared to women who never breastfed (OR=0.65, 95%CI: 0.58-0.73 for age &gt;30 years at first breastfeeding; OR=0.60, 95%CI: 0.53-0.69 for age &gt;35 years at last breastfeeding). Compared to women who never breastfed, women who last breastfed &lt; 10 years ago had 54% reduction of risk (OR= 0.46, 95%CI: 0.39-0.56) while women who last breastfed ≥ 30 years ago had 19% reduction of risk (OR=0.81, 95%CI: 0.74-0.88).
Conclusion: Breastfeeding regardless of age or duration was associated with reduced risk of ovarian cancer. Our findings support the benefit of breastfeeding as modifiable risk factor for ovarian cancer regardless of histologic subtypes, which has the potential for reducing the incidence this deadly disease.
Citation Format: Naoko Sasamoto, Ana Babic, Susan Jordan, Harvey Risch, Holly Harris, Mary Anne Rossing, Jennifer Doherty, Marc Goodman, Pamela Thompson, Susanne K. Kjær, Allan Jensen, Joellen Schildkraut, Linda Titus, Daniel Cramer, Elisa Bandera, Weiva Sieh, Valerie McGuire, Rebecca Sutphen, Celeste L. Pearce, Anna H. Wu, Malcolm Pike, Penelope Webb, Francesmary Modugno, Kathryn Terry. Breastfeeding pattern and ovarian cancer risk: Results from the Ovarian Cancer Association Consortium [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 640.