ERBB2 and breast cancer: Laboratory studies have shown that HER2-overexpressing breast cancer cell lines are susceptible to ADCC in the presence of trastuzumab (Carson et al, 2001; Parihar et al, 2002; Gennari et al, 2004), and in vivo activity of trastuzumab has been correlated with significantly increased number of peritumoral lymphocytes and monocytes and in vitro ADCC (Gennari et al, 2004; Arnould et al, 2006).