Although the mechanisms by which trastuzumab induces regression of HER2+ tumours are not known definitively, proposed mechanisms include potentiation of chemotherapy (Pegram et al, 1999), inhibition of tumour cell proliferation (Baselga et al, 1998; Sliwkowski et al, 1999), and facilitation of immune function through antibody-dependent cell-mediated cytotoxicity (ADCC) (Lewis et al, 1993; Sliwkowski et al, 1999; Repka et al, 2003). This evidence concerns the gene ERBB2 and neoplasm.