Most of these studies suggested that early breast cancer patients with HER2-overexpressing tumours get less benefit from adjuvant tamoxifen than those with HER2− tumours and have an increased risk of failing tamoxifen treatment (Borg et al. 1994, Carlomagno et al. 1996, Hu & Mokbel 2001, De Placido et al. 2003, Dowsett et al. 2005b, 2008, Rasmussen et al. 2008). This evidence concerns the gene ERBB2 and breast cancer.