In this post hoc analysis of a representative subset of postmenopausal, stage I-III patients with ER+HER2− tumor that participated in the randomized IKA trial of adjuvant tamoxifen versus nil, we observed an excellent outcome with no BCSS events during the first 10 years for node-negative patients with a ER+HER2− and 70-gene signature ultralow-risk tumor. The gene discussed is ERBB2; the disease is neoplasm.