ERBB2 and breast cancer: In several exploratory studies, patients who developed BM presented frequently genes altered in HER2 or EGFR/PTEN drive pathway in primary BC (27, 60), had a higher positivity of immunotherapy biomarkers (including TMB, MSI, and CD274) (61), and had more copy-number alterations and more actionable genetic alterations in BM than in primary BC (35).