In patients with early-stage or locally advanced HER2-positive breast cancer, the magnitude of clinical benefit and the acceptable safety profile in PEONY confirms the positive benefit:risk ratio of dual pertuzumab–trastuzumab neoadjuvant/adjuvant therapy, adding to the totality of the evidence of its use in the early setting, irrespective of time of surgery. This evidence concerns the gene ERBB2 and breast cancer.