Introduction: Trastuzumab, an HER2-targeting agents, has shown efficacy in metastatic HER2-positivebreast cancer patients. Single-agent clinical trials have evaluated therapeutic regimens using trastuzumab formetastatic breast cancer patients. The aim of our study is to evaluate the efficacy and safety of trastuzumabin combination with chemotherapy or hormone therapy in HER2-positive metastatic breast cancer patients. Methods: A literature research was conducted in PubMed and to identify appropriate studies from relevantreviews. Randomized controlled trials comparing chemotherapy or hormone therapy regimens in combinationwith trastuzumab were eligible. Dadta on clinical outcomes, including safety, efficacy, and patient characteristicswere collected. Results: Seven articles describing five trials were included in our systematic review and metaanalysis.Partners of trastuzumab included in trials were anthracycline, paclitaxel, docetaxel, anastrozole andletrozole. The addition of trastuzumab to chemotherapy improved the overall survival (HR=0.79, 95%CI 0.65-0.96), while to hormone therapy did not (HR=0.85 95%CI 0.56-1.30). All trastuzumab-containing regimensincreased cardiac toxicity (RR=3.37, 95%CI 1.26-9.02) and grade Ⅲ-Ⅳ adverse events. Conclusions: Our studysupports the addition of trastuzumab to chemotherapy which is effective and tolerated for metastatic breastcancer with HER2+ patients. Of note, more adverse events will occur followed the use of trastuzumab, especiallycardiac toxicity, with two treatment regimens.