ERBB2 and breast cancer: In the largest clinical series published so far, several alterations in oncogenes or tumor suppressor genes (TSGs) occurring more commonly in metastatic HR+ HER2-BC (mBC) than in early BC (eBC) specimens were reported [2–4]: the most frequent oncogenic mutations involved ESR1, ERBB2 and FGFR4 genes, while TP53, RB1, ATR, FAT1 and ARID1 were the most commonly altered TSGs.