ERBB2 and breast cancer: Insight into the heterogeneity at genomic level has revealed that the intrinsic subtypes of HER2‐positive breast cancer are distributed to luminal A, luminal B, HER2‐enriched, and basal‐like based on Prediction Analysis of Microarray 50, with around 70% or 80% belonging to luminal subtypes, characterized by the enrichment of luminal gene clusters.18