Durable complete response in HER2-positive breast cancer: a multicenter retrospective analysis.

PURPOSE: Though advanced and metastatic epidermal growth factor receptor 2 (HER2)-positive disease is not curable, a small proportion of patients with HER2-positive metastatic breast cancer remain in prolonged complete remission with anti-HER2 treatment. We hypothesized that some cases of HER2-positive metastatic breast cancer may be curable. In this large, multicenter retrospective study, we aimed to assess the long-term outcomes for patients with a durable response to trastuzumab.

METHODS: We retrospectively evaluated the data of patients diagnosed with HER2-positive metastatic breast cancer who received trastuzumab for more than 2 years as the first-line treatment. Patients diagnosed between April 1, 2001 and December 31, 2014 at 19 institutions in Japan were included in the analysis. From 124 potential subjects, 16 were excluded and 108 were evaluated.

RESULTS: The median follow-up length was 7.7 years. Disease progression occurred in 44/108 (40.7%) patients and 13/108 (12%) patients died. The median progression-free survival was 11.2 years, and as more than 80% of patients were alive 10 years after metastatic breast cancer diagnosis. Of the 108 patients, 57 achieved a clinical complete response. Trastuzumab therapy was interrupted for 27 (47.4%) of these patients (based on the doctor's recommendation for 19 patients, owing to adverse events for 4 patients, owing to unknown reasons for 3 patients, and at the request of 1 patient). Disease progression occurred in 4 of the 27 patients after the interruption of trastuzumab treatment. The median duration of trastuzumab therapy for all 27 patients was 5.1 years (0.9-9.3 years).

CONCLUSION: We found that some patients showed no evidence of disease after the interruption of trastuzumab therapy. Discontinuation of maintenance trastuzumab in this patient population after a limited time should be explored cautiously while awaiting a global collaborative effort for a randomized trial.