The recombinant humanised anti-HER2 trastuzumab (Herceptin), has high affinity for HER2 and induces its downregulation, with inhibition of proliferation of breast cancer cell lines in vitro and in vivo (Mendelsohn and Baselga, 2000; Vincenzi et al, 2008). The gene discussed is ERBB2; the disease is breast cancer.