Benefits of adjuvant treatment including trastuzumab in HER2-positive pT1a-bN0M0 breast cancer: a systematic review and meta-analysis

BACKGROUND: Although trastuzumab has been shown to be beneficial for treating patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, information regarding its benefits is limited to very low-risk cases with tumours ≤1 cm and without lymphatic metastases (pT1abN0). The present meta-analysis integrates information from literature and determines the benefit of trastuzumab in pT1abN0, HER2-positive breast cancer patients. METHODS: PubMed, MEDLINE, and EMBASE databases were searched for studies published before Sep 30, 2019. Our primary endpoint was tumor recurrence, whether provided as overall or distant recurrences. RESULTS: Seven studies involving 1,181 patients with pT1abN0, HER2-positive breast cancer were included in the systemic review. The median follow-up periods ranged from 37 to 78 months. The patients in the trastuzumab arm had generally inferior profiles such as higher rate of T1b, grade 3, and hormone negative cases, among available studies. Concomitant chemotherapy was more commonly applied in the trastuzumab arm (75–100% vs. 0–42%), and the hormone therapy application was similar in both arms (20–66%). In a pooled analysis of seven available studies, patients treated with trastuzumab had less overall recurrence relative to controls, with an odds ratio of 0.201 [95% confidence interval (CI): 0.100–0.404, P<0.001]. Five studies were available for a pooled analysis of distant recurrence. Although the results were not significant (P=0.115), distant recurrence did not occur in 237 patients treated with trastuzumab, but did occur in 16 out of 436 control patients. The odds ratio for distant recurrence was 0.328 (95% CI: 0.082–1.311). CONCLUSIONS: The adjuvant treatment including trastuzumab was shown to reduce overall recurrence. Distant recurrence may also be reduced, as it did not occur among the 237 patients who underwent trastuzumab treatment.