Effect of Trastuzumab among HER2-Positive Breast Cancer Patients that Achieved Pathologic Complete Response after Neoadjuvant Chemotherapy

Background: We sought to investigate the incremental benefit of trastuzumab in patients with HER2-positive breast cancer who achieved a pathologic complete response (pCR) after neoadjuvant chemotherapy (NACT). Methods: The data of HER2-positive invasive breast cancer patients treated with NACT and achieving pCR were obtained from the institutional database. Patients were categorized according to trastuzumab administration. The Kaplan-Meier method and log-rank estimates were used to test the association between trastuzumab administration and survival. Univariate and multivariate Cox regressions were used to obtain hazard ratios. Results: Of 223 patients, 83 (37.2%) were treated with NACT without trastuzumab and 140 (62.8%) were treated with NACT plus trastuzumab for 1 year. After a median follow-up of 67 months, the trastuzumab group showed improved relapse-free survival compared with the no-trastuzumab group (95.7 vs. 87.8%, hazard ratio = 0.31, p = 0.028). No significant difference in distant disease-free survival or overall survival was observed (p = 0.250 and 0.432, respectively). Multivariate analysis identified endocrine therapy and trastuzumab administration to be associated with decreased risk of relapse (p = 0.018 and 0.030, respectively). Conclusion: The administration of trastuzumab should be considered standard treatment for HER2-positive patients who have achieved pCR after NACT alone.