ERBB4 and breast cancer: Triple-negative and basal-like breast cancer subtypes, which exhibit a high degree of gene expression profile overlap (50, 52, 53) [reviewed in (54–56)], are characterized by elevated expression of EGFR (50) [reviewed in (51)]; thus, it has been hypothesized that ERBB4-EGFR heterodimers in these breast cancer subtypes may function as oncoproteins [reviewed in (21)].