PURPOSE: In the last decade trastuzumab biosimilars became more and more frequent. Among their uses, from several years, they have been available in Europe for the treatment of HER2-positive metastatic breast cancer, as an alternative to Herceptin®. METHODS/PATIENTS: This meta-analysis aimed to analyze the available literature with particular focus on phase 3 randomized clinical trials (RCTs) comparing adverse events between trastuzumab biosimilar and originator. A systematic review was conducted in Pubmed and Scopus to include all phase 3 RCTs related to trastuzumab in patients with HER2-positive breast cancer and published up to July 31, 2023. Of the 508 records identified, 14 articles were meta-analyzed for safety information, including serious treatment emergent adverse events, death-related adverse events, neutropenia, leukopenia, infections, increased ALT, increased AST, anti-drug antibody, and neutralizing antibody. RESULTS: Included patients had an early breast cancer (N=2,877) or a metastatic breast cancer (N=2,603). No significant difference in death-related adverse events was found for trastuzumab biosimilar and originator when evaluated for an early breast cancer in the neoadjuvant phase (Risk Ratio [RR], 1.30; 95% confidence interval [CI], 0.47-3.59; I2 = 0%; p = 0.57) and overall (RR, 0.43; 95%CI, 0.11-1.66; I2 = 20%; p = 0.26), and for metastatic breast cancer (RR, 0.61; 95%CI, 0.30-1.26; I2 = 0%; p = 0.85). CONCLUSIONS: No difference was also observed for all other safety outcomes as in accordance with clinical studies necessary for the registration and approval of a biosimilar at a European level.< Réduire