ERBB2 and breast cancer: Breast cancer data similarly identify enrichment of ERBB2 alterations in BrM.36,37,38 It remains to be seen whether this enrichment is the result of selective tropism for the brain or a reflection of the central nervous system serving as a sanctuary site for disease, owing to the poor blood brain barrier penetration of ERBB2-directed therapies.39 We also identified significant enrichment in PTPRT alterations in BrM tissue.