The best efficacy and positive therapeutic outcome with trastuzumab is observed in women with tumours that overexpress, have an amplification, or have high activity of ErbB-2 (Muss et al, 1994; Nabholtz and Slamon, 2001; Slamon and Pegram, 2001; Menendez et al, 2006). This evidence concerns the gene ERBB2 and neoplasm.