ERBB3 and cancer: In order to identify proteins which interact with each phosphorylated site of four EGF receptors, protein microarrays consisting of almost all of the SH2 and PTB domains in the human genome were tested against each phosphorylated site in EGFRs, and not only identified many new interactions, but unexpectedly revealed that EGFR and HER2 showed a more promiscuous pattern of interactions than HER3 as the affinity thresholds were lowered, suggesting a reason for why EGFR and HER2 are frequently overexpressed in cancers whereas HER3 is not [63].