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.).