The characteristics of HER2-positive microinvasive breast cancer and the necessity of systemic adjuvant therapy in these patients: a multicenter real-world study.

Abstract

Background: There is currently a lack of sufficient evidence on the prognosis of human epidermal factor receptor 2 (HER2)-positive microinvasive breast cancer (MIBC) and whether chemotherapy (CT) and targeted therapy can bring benefits.

Objectives: To explore the prognosis and treatment of HER2-positive MIBC.

Design: A retrospective multicenter study.

Methods: In this multicenter real-world study, we consecutively enrolled patients who received local management and were diagnosed with lymph node-negative HER2-positive MIBC from January 2010 to December 2020.

Results: A total of 163 patients were included. Thirty-nine patients (23.9%) received adjuvant CT, of which 12 patients (7.4%) received CT combined with trastuzumab. One patient received trastuzumab therapy alone. In total, nine patients (5.5%) experienced recurrence, and the 3-year disease-free survival (DFS) rate and 5-year DFS rate were both 95.1%. Kaplan-Meier analysis showed that patients aged ⩽40 had worse outcomes than those aged >40 (3-year DFS rate 81.8% vs 96.1%, p = 0.046). Using propensity score matching, we matched patients who received trastuzumab or CT ± trastuzumab with those who did not receive treatment based on age, tumor size, estrogen receptor status, and number of infiltration lesions. Patients who received targeted therapy or CT ± targeted therapy did not achieve further improvement in 3-year DFS rate (95.0% vs 95.0%, p = 0.630).

Conclusion: HER2-positive MIBC has relatively good prognosis, and age ⩽40 years might be a poor prognostic factor. CT or targeted therapy seemed to bring little benefit for MIBC. Further prospective studies are needed to assess potential benefits of management for MIBC patients under the age of 40 years in the future.