ERBB2 and breast cancer: However, HER2 breast cancer disease is heterogeneous, as supported by: (a) the presence of a consistent heterogeneity of genomic profile, with the presence of HR+/HER2+tumors exhibiting more mutations in genes involved in homologous recombination, TGF-beta, and WNT signaling pathways than HR-/HER2+ tumors [376]; (b) the gene expression profiling with about 75% of tumors exhibiting a HER2-enriched transcriptional landscape, but with some tumors displaying a luminal B or luminal A gene expression profile [377].