Abstract B21: Intratumoral hormone receptor heterogeneity is a characteristic of high-grade breast cancer and is associated with inter-laboratory hormone receptor status discordance

Introduction: Intratumoral hormone receptor (HR) heterogeneity may have implications for molecular classification of breast tumors which, in turn, may impact clinical decision making and epidemiologic research. Prior studies show that 10-20% of patients have discordant estrogen receptor (ER) or progesterone receptor (PR) status upon repeat assay. While technical factors contribute to this discordance, intratumoral HR heterogeneity may also play a role. We examined the association between intratumoral HR heterogeneity, measured at a single research laboratory, and clinical HR status, tumor characteristics and demographic variables. Methods: We used paraffin-embedded blocks from 932 invasive breast cancer cases, of which 497 were African-American, from the population-based Carolina Breast Cancer Study Phase 3, part of the African-American Breast Cancer Epidemiology and Risk (AMBER) Consortium. Two to four 1mm tumor cores per case were assembled into tissue microarrays and stained for ER and PR at a single research laboratory. ER and PR status (positive: ≥1% positive tumor cells; negative: Results: Of 932 cases, 95 (10%) had ER heterogeneity while 149 (16%) had PR heterogeneity. Overall, there was high agreement between clinical and research ER status (93% concordance; 95% confidence interval (CI) 92-95%) and PR status (89%; 95%CI 87-91%), consistent with previously reported inter-laboratory concordance rates. However, agreement was lower in cases with intratumoral heterogeneity (ER: 74%; 95%CI 65-83% and PR: 61%; 95%CI 53-69%), relative to homogeneous cases (ER: 96%; 95%CI 95-97% and PR: 94%; 95%CI 92-96%). Obesity, defined as BMI≥30kg/m2, was associated with increased odds of ER heterogeneity (adjusted odds ratio (OR)obese vs. normal weight 1.76; 95%CI 0.95-3.29), with a stronger association among postmenopausal women (OR 2.52; 95%CI 1.14-5.56). High tumor grade was associated with increased odds of both ER and PR heterogeneity (ORgrade III vs. I 3.14; 95%CI 1.47-6.70 and ORgrade III vs. I 2.28; 95%CI 1.26-4.14, respectively). There were no associations between intratumoral heterogeneity and age, race or menopausal status. Conclusions: Intratumoral heterogeneity may account for a portion of the well-documented inter-laboratory discordance in ER and PR status, with implications for tumor subtype classification. Intratumoral heterogeneity was more prevalent in high grade tumors, indicating that it may be a feature of aggressive breast cancer. Furthermore, obese postmenopausal women were more likely to have intratumoral ER heterogeneity, suggesting a potential mechanism underlying the association between obesity and worse breast cancer prognosis. Although these data do not support an association between intratumoral heterogeneity and race, given that both high grade disease and obesity are more common in African Americans, future studies should explore a possible role for intratumoral heterogeneity in breast cancer racial disparities. Citation Format: Emma H. Allott, Joseph Geradts, Xuezheng Sun, Stephanie M. Cohen, Thaer Khoury, Wiam Bshara, Gary Zirpoli, Julie R. Palmer, Christine B. Ambrosone, Andrew F. Olshan, Melissa A. Troester. Intratumoral hormone receptor heterogeneity is a characteristic of high-grade breast cancer and is associated with inter-laboratory hormone receptor status discordance. [abstract]. In: Proceedings of the Seventh AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 9-12, 2014; San Antonio, TX. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2015;24(10 Suppl):Abstract nr B21.