Abstract PR-04: Association of HER2/GRB7 co-expression with Indigenous American ancestry and breast cancer clinical-pathological features
Authors: Vargas Laura Rey , Bejarano Lina Maria , Henao Juan Carlos Mejia , Villegas Luz Fernanda Sua , Andrade Jhon Faustino Bastidas , Gómez Carlos Andrés Ossa , Fejerman Laura , Salas Maria Carolina Sanabria , Gomez Silvia Juliana Serrano 
Published: January 2022

Introduction: Breast cancer is the most prevalent cancer in women worldwide. It is a heterogeneous disease that has been classified into intrinsic subtypes based on gene expression analyses. Previous studies have reported a higher proportion of HER2-positive (HER2+) tumors in Hispanics/Latinas, compared to Non-Hispanic White women, characterized by their aggressive phenotype. A gene expression analysis of breast tumor tissues from Colombian women reported that patients with a higher Indigenous American (IA) ancestry expressed higher mRNA levels of ERBB2, and of other genes in the HER2-amplicon region (17q12) such as GRB7. Although the expression of HER2 and GRB7 is highly correlated, it has been reported that these proteins might also be expressed independently. It is still unclear whether IA ancestry is associated with the co-expression of HER2/GRB7, or only with one of these two proteins. Aim of the study: To explore differences in HER2 and GRB7 protein expression according to genetic ancestry and the presentation of clinical-pathological features in Colombian women with breast cancer. Methods: A total of 517 Colombian breast cancer patients from different health institutions were included. For genetic ancestry estimation, 106 ancestry informative markers were genotyped from non-tumoral DNA. The protein expression of HER2 and GRB7 was evaluated in paraffin blocks with tumoral tissue by immunohistochemistry by a single pathologist. We tested the association between genetic ancestry and protein expression of HER2, GRB7, and the co-expression of both using logistic and multinomial logistic regression models. Results: Higher IA ancestry fractions were observed in patients with HER2+ compared to HER2- tumors (46% vs 41%, respectively, p = 0.013). We found higher odds of having HER2+ (OR=1.65, 95% CI, 1.05-2.63, p=0.0293) and GRB7+ tumors (OR=1.92, 95% CI, 1.03-3.56, p=0.0376) for every 25% increase in the IA ancestry proportion. The association between IA ancestry and HER2/GRB7 co-expression was influenced by estrogen receptor (ER) status. Patients with a higher IA ancestry (&gt;42%) and with ER+ subtypes presented higher odds of having HER2+/GRB7- breast tumors (OR=3.59, 95% CI, 1.11-11.65, p=0.0327), whereas ER- patients with high IA ancestry tended to have HER2+/GRB7+ tumors (OR=2.27, 95% CI, 0.69 - 7.45, p=0.1730). The co-expression of these proteins was found associated with advanced clinical stages (p=0.018), less differentiated tumors (p=0.005), and a higher proliferation index (p&lt;0.001), compared to HER2+/GRB7- and HER2-/GRB7- tumors. Conclusions: Our results confirm the previously reported association between IA ancestry and HER2 expression in breast tumors and suggest that HER2/GRB7 co-expression in patients with high AI ancestry may change according to the ER status. This event also correlates with unfavorable clinical-pathological features.

Citation Format: Laura Rey Vargas, Lina Maria Bejarano, Juan Carlos Mejia Henao, Luz Fernanda Sua Villegas, Jhon Faustino Bastidas Andrade, Carlos Andrés Ossa Gómez, Laura Fejerman, Maria Carolina Sanabria Salas, Silvia Juliana Serrano Gomez. Association of HER2/GRB7 co-expression with Indigenous American ancestry and breast cancer clinical-pathological features [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PR-04.