Trastuzumab delivered with chemotherapy for patients with HER2-positive breast cancer in the metastatic1 and adjuvant settings2, 3, 4 resulted in improved treatment outcomes, and long-term follow-up has confirmed these benefits.5, 6 A 12-month treatment duration with adjuvant trastuzumab was chosen arbitrarily for the pivotal licensing trials2, 3, 4 and, subsequently, became standard. Here, ERBB2 is linked to breast cancer.