Although treatment of HER2+ breast cancer is increasingly personalized and evolving (6, 7), trastuzumab remains a crucial care component, offering women a 33% reduction in breast cancer mortality in early stage disease [ratio of annual death rates = 0.67, 95% confidence interval (CI), 0.61–0.73; ref. 8] and an 18% reduction in overall survival in women with metastatic disease (pooled HR = 0.82; 95% CI, 0.71–0.94; ref. 9). Here, ERBB2 is linked to breast carcinoma.