ERBB2 and breast cancer: Furthermore, the identification of five intrinsic molecular subgroups of breast cancer based on the PAM50 gene expression classifier—luminal A, luminal B, HER2-enriched, basal-like, and normal-like—has shed light on the intricate molecular heterogeneity within the disease, suggesting that such a diversity may be crucial in determining the prognosis and treatment response of patients [8].