There were 2 cases with discordant receptor classification between primary tumor and BrM by immunohistochemistry (n = 1 ER+/PR+/HER2- Luminal A primary converted to a TNBC BrM, and n = 1 TNBC primary converted to an ER+/PR+/HER2- Luminal A BrM) (Table 1; Supplementary Figure S2). This evidence concerns the gene ERBB2 and neoplasm.