ERBB3 and invasive breast carcinoma: However, the importance of ERBB3 activity in promoting ERBB-driven cancers is suggested by its ability to cooperate with ERBB2 to enhance cellular transformation [8] and the tumor regression associated with short hairpin RNA-based (shRNA-based) knockdown of ERBB3 in mouse models of ERBB2-positive breast cancer (BrCa) [9].