ESR1 and neoplasm: For example, data from the randomised open-label TAnDEM phase-III trial suggested that the addition of trastuzumab to anastrozole contributed to significant improvement in PFS in patients with ER+/HER2+ tumours compared to anastrozole treatment alone (5.6 months vs 3.8 months; P < 0.006) (Kaufman et al. 2009).