Due to the wide use of screening mammography, there was an increasing trend for pT1a‐pT1b breast cancer (up to 20% of newly diagnosed breast cancer).7, 8 Despite the dramatic effect of anti‐HER2 agents, no available randomized clinical trials examined the efficacy of adjuvant trastuzumab in pT1a, b HER2+ breast cancers.9, 10 Besides, the existing retrospective studies reached conflicting results regarding the prognosis of HER2+ T1a, b tumors. Here, ERBB2 is linked to breast carcinoma.