Notably, in the early 2000s, extensive work by Perou, Sørlie, and colleagues classified breast cancers into five main molecular subclasses, based on gene expression profiles called the “intrinsic subtypes”: Luminal A and Luminal B, human epidermal growth factor type 2 enhanced (HER2), Basal-like (BLBC), and Normal-like (NLBC) breast cancers (Perou et al., 2000; Sørlie et al., 2001). Here, ERBB2 is linked to breast carcinoma.