ERBB2 and breast carcinoma: Without the confounding effect of trastusumab, a cohort of 98 HER2+ T1a, b breast cancers with no adjuvant treatment showed significant worse disease‐free survival and distant disease‐free survival compared to HER2‐ subgroup.26 Another study revealed small (<1 cm) HER2+ breast cancer has a high risk for recurrence with HR up to 8.8.27