NCDB analysis of adding systemic to local therapy for stage I pT1aN0M0 HER2+ breast cancer

Small invasive breast cancers (BCs) with tumor sizes ≤ 5 mm (T1a) are associated with and excellent prognosis without systemic therapy. Although HER2 overexpression (HER2+) is associated with a higher risk of recurrence and poorer clinical outcomes, in the absence of HER2 directed therapy, it remains unclear whether adjuvant systemic therapy is necessary in node-negative patients diagnosed with HER2+ invasive BCs ≤ 5 mm (pT1aN0M0). Propensity matched analysis of the National Cancer Database (2004-2017) found that addition of systemic therapy after surgical excision of pT1aN0M0 HER2+ BC was not associated with superior overall survival.