Several studies have identified HER2-positive breast cancers as having a more aggressive biology and being associated with inferior outcomes, including shorter time to disease progression and shorter overall survival.17,18 The advent of anti-HER therapies has significantly overridden this poor prognosis, so that patients with HER2-positive metastatic breast cancer treated with modern HER2-targeted therapies now experience outcomes comparable, if not superior, to their counterparts with HER2-negative disease.19 This evidence concerns the gene ERBB2 and breast cancer.