Clinical, pathological and PAM50 gene expression features of HER2-low breast cancer

Càncer de mama; Genòmica del càncer; Recerca translacional Cáncer de mama; Genómica del cáncer; Investigación traslacional Breast cancer; Cancer genomics; Translational research Novel antibody-drug conjugates against HER2 are showing high activity in HER2-negative breast cancer (BC) with low HER2 expression (i.e., 1+ or 2+ and lack of ERBB2 amplification). However, the clinical and molecular features of HER2-low BC are yet to be elucidated. Here, we collected retrospective clinicopathological and PAM50 data from 3,689 patients with HER2-negative disease and made the following observations. First, the proportion of HER2-low was higher in HR-positive disease (65.4%) than triple-negative BC (TNBC, 36.6%). Second, within HR-positive disease, ERBB2 and luminal-related genes were more expressed in HER2-low than HER2 0. In contrast, no gene was found differentially expressed in TNBC according to HER2 expression. Third, within HER2-low, ERBB2 levels were higher in HR-positive disease than TNBC. Fourth, HER2-low was not associated with overall survival in HR-positive disease and TNBC. Finally, the reproducibility of HER2-low among pathologists was suboptimal. This study emphasizes the large biological heterogeneity of HER2-low BC, and the need to implement reproducible and sensitive assays to measure low HER2 expression. This work was supported by the grants from the European Union’s Horizon 2020 Research and Innovation Programme under Grant agreement No. 847912 (to A.P.), the Instituto de Salud Carlos III-PI16/00904 (to A.P.), Pas a Pas (to A.P.), Save the Mama (to A.P.), Breast Cancer Now-2018NOVPCC1294 (to A.P.), Fundación Científica Asociación Española Contra el Cáncer-Ayuda Postdoctoral AECC 2017 (to F.B.-M.), Fundación SEOM, Becas FSEOM para Formación en Investigación en Centros de Referencia en el Extranjero 2018 (to T.P.) and PhD4MD - Departament de Salut expedient SLT008/18/00122 (to N.C.).