ERBB2 and breast cancer: BMs are more common in certain breast cancer subtypes, such as human epidermal growth factor receptor 2 (HER2)–positive breast cancer, which has a higher incidence of BMs (35%-50%) but generally yields better survival outcomes compared with HER2-negative disease.6,7 Triple-negative breast cancer (TNBC) is associated with a high frequency (34%) of BMs and poor survival outcomes.8,9 TNBC is also associated with gBRCA1 pathogenic mutations, which carry an elevated risk of brain-first recurrence.10 Compared with gBRCA2 carriers, BM is more prevalent among patients carrying gBRCA1 mutations.