ERBB2 and neoplasm: While the MSK cohort only included HR+/HER2- tumours (n = 1116), biospecimens in the Inserm cohort (n = 216) contained all major breast cancer subtypes including 143 (66.2%) HR+/HER2-, 51 (23.6%) TNBC and 14 (6.5%) HER2-enriched MBCs.