ESR1 and breast carcinoma: It must be highlighted that because the multigene classifiers for the conventional breast cancer biomarkers (ER, PgR, Ki67, and HER2) used in this study are trained on histopathological labels, it is not surprising that tumors assigned a positive HER2GEX status are not necessarily classified as HER2-enriched by the conventional PAM50 molecular subtype classifier.