The target protein, HER2, is involved in regulating cell growth, survival, adhesion and differentiation (Yarden, 2001) and found to be overexpressed on the tumour cell surface in ∼20% of all human breast cancers (Slamon et al., 1987), which results in an aggressive phenotype with a poor clinical outcome for patients (Winstanley et al., 1991). Here, ERBB2 is linked to breast cancer.