Abstract C54: Parity and breastfeeding associations with familial estrogen receptor-negative breast cancer

Abstract

Abstract Background. Disparities exist in the incidence of aggressive breast cancer characteristics by race. In order to characterize potential contributors to breast cancer disparities, we studied breastfeeding and parity characteristics in a sample of African American families with breast cancer. Based on evidence suggesting that lack of breastfeeding may influence the development of aggressive tumors, we performed both case/non-case comparisons and case-only comparisons according to receptor status. We hypothesized that African American women who developed estrogen receptor (ER)-negative and triple negative breast cancer are less likely to have ever breastfed, a shorter breastfeeding history, and more children than their sisters who did not develop breast cancer. Methods. In a sample of 281 African American women (197 breast cancer cases and 84 unaffected sisters of cases) from 106 families, we examined differences in reproductive risk factor profiles (including parity a breastfeeding histories) between women diagnosed with breast cancer and their unaffected sisters using t-tests and chi-square tests. In cases only, we characterized breastfeeding duration and parity according to breast cancer subtypes using t-tests. Results. African American women who developed breast cancer had an earlier age at menarche than their unaffected sisters (12.3 versus 13.1 years; p=0.01). Breast cancer cases also were more likely to have had a hysterectomy (49% versus 32%; p=0.02) and less likely to have used hormone therapy (19% versus 33%; p=0.01) compared to their sisters. Approximately 40% of cases reported ever breastfeeding compared to 50% of their non-case relatives; however this was not statistically significant (p=0.17). In case-only analyses, we observed a statistically significant shorter duration of breastfeeding in women with ER-negative compared to ER-positive tumors (11.3 versus 36.7 weeks; p=0.01), and in women with triple negative tumors compared to non-triple negative tumors (8.7 versus 35.1 weeks; p=0.00001). In terms of parity, women with ER-negative tumors had fewer births compared to ER-positive (1.54 versus 2.07 births; p=0.04). Similarly, women with triple negative tumors had significantly fewer births than cases who did not have triple negative tumors (1.39 versus 3.19 births; p=0.01). Conclusion. In a sample of African Americans with a notable family history of breast cancer, short duration of breastfeeding may represent an additional and modifiable risk factor for aggressive breast cancer. These findings support literature on the association of breastfeeding and ER-negative tumors, providing additional insight into the possible prevention of familial breast cancer. Studies including African Americans to further replicate these findings and shed light on potential biologic mechanisms are needed. Citation Format: Mattie Dibbell, Deborah Erwin, Detric Johnson, Lina Jandorf, Veronica Meadows Ray, Heather Ochs-Balcom. Parity and breastfeeding associations with familial estrogen receptor-negative breast cancer. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr C54.