ERBB2 and cancer: Conversely, trastuzumab co-treatment was ineffective at enhancing the chemotherapy efficacy in HER2-negative cancer cells exogenously treated with recombinant HRGβ1 or in cancer cells engineered to overexpress a structural deletion mutant lacking the transmembrane domain of HRGβ1 that, therefore, could be secreted, thus preventing the autocrine actions of HRGβ1 via the HER receptors (Menendez et al, 2005, 2006).