Prognostic Value of the Evolution of HER2-Low Expression after Neoadjuvant Chemotherapy

PURPOSE: Patients with human epidermal growth factor receptor 2 (HER2)–low advanced breast cancer can benefit from trastuzumab deruxtecan. Given the unclear prognostic characteristics of HER2-low breast cancer, we investigated the prognostic characteristics of HER2-low expression from primary tumor to residual disease after neoadjuvant chemotherapy (NACT). MATERIALS AND METHODS: The data of HER2-negative patients receiving NACT at our center were collected. Pathological complete response (pCR) rate were compared between HER2-0 and HER2-low patients. The evolution of HER2 expression from primary tumor to residual disease and its impact on disease-free survival (DFS) were examined. RESULTS: Of the 690 patients, 494 patients had HER2-low status, of which 72.3% were hormone receptor (HR)–positive (p < 0.001). The pCR rates of HER2-low and HER2-0 patients (14.2% vs. 23.0%) showed no difference in multivariate analysis regardless of HR status. No association was observed between DFS and HER2 status. Of the 564 non-pCR patients, 57 (10.1%) changed to HER2-positive, and 64 of the 150 patients (42.7%) with HER2-0 tumors changed to HER2-low. HER2-low (p=0.004) and HR-positive (p=0.010) tumors before NACT were prone to HER2 gain. HER2 gain patients had a better DFS compared with HER2-negative maintained patients (87.9% vs. 79.5%, p=0.048), and the DFS of targeted therapy group was better than that of no targeted therapy group (92.4% vs. 66.7%, p=0.016). CONCLUSION: Although HER2-low did not affect the pCR rate and DFS, significant evolution of HER2-low expression after NACT creates opportunities for targeted therapy including trastuzumab.