Abstract B119: Presence of etiologic heterogeneity by breast tumor subtypes in Hispanic women with unique reproductive risk factor patterns
Authors: Martinez Maria Elena , Wertheim Betsy , Natarajan Loki , Schwab Richard , Bondy Melissa , Daneri-Navarro Adrian , Meza-Montenegro Maria Mercedes , Gutierrez-Millan Luis Enrique , Brewster Abenaa , Komenaka Ian K. , Thompson Patricia A. 
Published: May 2015

Abstract
Background: Published data support the presence of etiologic heterogeneity by breast tumor subtype, but few studies have assessed this in Hispanic populations. Methods: We assessed tumor subtype prevalence and associations between reproductive factors and tumor subtypes in 1041 women of Mexican descent (559 U.S. and 482 Mexico) who participated in the Ella Binational Breast Cancer Study. Multinomial logistic regression comparing human epidermal growth factor receptor 2 positive tumors (HER2+, regardless of ER or PR status) and triple negative breast cancer (TNBC) to hormone receptor positive (HR+) tumors was conducted. Results: A higher proportion of ER- tumors was shown for women in Mexico (40.5%) vs. those in the U.S. (27.2%) and slightly higher proportions of HR+ (61.2% vs. 57.9%) and HER2+ (23.8% vs. 20.3%) tumors were observed in the U.S. compared to Mexico. Prevalence of TNBC was 16.7% overall; the percentage was higher for Mexican vs. U.S. women (19.5% vs. 14.5%). After adjustment for age and country of residence, compared to women with HR+ tumors, those with a later age at first pregnancy were significantly less likely to have TNBC (odds ratio [OR]=0.61; 95% confidence interval [CI]=0.39-0.95), whereas those with ≥ 3 full-term pregnancies were significantly more likely to have TNBC (OR=1.68; 95% CI=1.10-2.55). Patients who reported breastfeeding for &gt;12 months were over twice as likely to have TNBC than HR+ tumors (OR=2.14; 95% CI=1.24–3.68). A lower odds of TNBC was shown for longer menstruation duration, whether prior to first pregnancy (OR=0.78; 95% CI= 0.65–0.93 per 10 years) or prior to menopause (OR=0.79; 95% CI, 0.69–0.91 per 10 years). Associations comparing HER2+ to HR+ tumors were weak or non-existent except for the interval between last full-term pregnancy and breast cancer diagnosis. Conclusions: Findings show etiologic heterogeneity by tumor subtype in a population of Hispanic women with a unique reproductive profile. Given that Hispanic women have higher risk of breast cancer-specific mortality than non-Hispanic whites, our findings add to growing evidence of opposing effects of reproductive factors on breast tumor subtypes, which may partly explain disparities in outcomes.
Citation Format: Maria Elena Martinez, Betsy Wertheim, Loki Natarajan, Richard Schwab, Melissa Bondy, Adrian Daneri-Navarro, Maria Mercedes Meza-Montenegro, Luis Enrique Gutierrez-Millan, Abenaa Brewster, Ian K. Komenaka, Patricia A. Thompson. Presence of etiologic heterogeneity by breast tumor subtypes in Hispanic women with unique reproductive risk factor patterns. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B119.