Abstract P4-07-10: Gene expression profiling in immunophenotypic triple negative breast carcinomas harboring HER-2 amplification identifies tumors with distinct molecular signatures and increased ERBB2 gene expression

Abstract

Abstract Introduction: Breast carcinomas can be classified by hormone receptors and human epidermal growth factor receptor-2 (HER-2) status. HER-2 status is assessed using immunohistochemistry (IHC) and/or fluorescent in situ hybridization (FISH). Immunophenotypic triple negative breast cancers (iTNBC) may harbor an amplification of HER-2 detected by FISH (iTNBC-FISHAmp) or may be negative by FISH (iTNBC-FISHNeg). The discrepancy between protein expression and gene amplification in these tumors poses relevant questions on tumor biology and for treatment implications. Here we investigate iTNBC-FISHAmp and iTNBC-FISHNeg by gene expression profile. Methods: A total of 40 iTNBC were selected. HER-2 IHC scores (0 or 1+) were annotated. All the tumors were tested by FISH showing 20 iTNBC-FISHAmp and 20 iTNBC-FISHNeg. The tumor morphology was reviewed by 2 pathologists, and stromal tumor infiltrating lymphocytes (sTILs) were estimated as high (H-sTILs) or low (L-sTILs). The areas of tumor with best cellularity were selected for RNA extraction. Gene expression profiling using a panel of 776 genes across 33 biological signatures was performed using Nanostring technology. Results: ERBB2 gene expression was significantly higher in iTNBC-FISHAmp when compared to iTNBC-FISHNeg tumors (p<0.001). ERBB2 gene expression was significantly higher in tumors with IHC 1+ when compared to tumors with IHC 0 (p<0.001). Genes related to the biologic stromal signature showed a lower expression in iTNBC-FISHAmp when compared with iTNBC-FISHNeg (p=0.015). All tumors were classified as basal-like molecular subtype. The histologic presence of sTILs had no correlation with ERBB2 gene expression. Tumors with H-sTILs significantly correlated with the multiple biological signatures related to inflammation and immunoresponse, including PDL1, PD1, TIGIT, CD8, Cytotoxic cells, TREG (regulatory T cell), TIS (tumor inflammatory signature); while tumors with L-sTILs significantly correlated with B7-H3, stromal, AR, and claudin-low signatures. Conclusions: Our results demonstrate that iTNBC tumors are a heterogeneous entity at the molecular level. In iTNBC-FISHAmp, ERBB2 gene is significantly up-regulated despite low HER-2 protein expression. Tumors with HER-2 IHC 1+ are associated with higher gene expression than tumors with IHC 0. iTNBC-FISHAmp show a lower expression of genes related to biologic stoma signature with possible implications on biology of tumor microenvironment. The histological assessment of sTILs in iTNBC correlates with multiple gene expression signatures that are closely related to tumor immunogenicity and sensitivity to immunotherapy. Further studies are needed to establish the functional role of HER-2 signaling in these tumors. Citation Format: Paolo Cotzia, Theodore Vougiouklakis, Ursula Andreo, George Jour, Christopher Schwartz, Maryann Kwa, Sylvia Adams, Francisco Esteva, Deborah Axelrod, Freya Schnabel, Matija Snuderl, Farbod Darvishian. Gene expression profiling in immunophenotypic triple negative breast carcinomas harboring HER-2 amplification identifies tumors with distinct molecular signatures and increased ERBB2 gene expression [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-07-10.