ERBB2 and breast cancer: Ubiquitously, trials of doublet HER2-targeted therapy without chemotherapy have achieved a pathologic complete response in 20%-40% of patients.21 Though all-comers with HER2+ breast cancer who receive dual anti-HER2 therapy with chemotherapy are more likely to achieve a pCR, the successful identification of patients with HER2 oncogene-dependent tumors who may respond without chemotherapy would lead to a paradigm shift in personalized neoadjuvant treatment for HER2+ breast cancer.