Introduction: Trastuzumab, an HER2-targeting agents, has shown efficacy in metastatic HER2-positive breast cancer patients. Single-agent clinical trials have evaluated therapeutic regimens using trastuzumab for metastatic breast cancer patients. The aim of our study is to evaluate the efficacy and safety of trastuzumab in 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 relevant reviews. Randomized controlled trials comparing chemotherapy or hormone therapy regimens in combination with trastuzumab were eligible. Dadta on clinical outcomes, including safety, efficacy, and patient characteristics were collected. Results: Seven articles describing five trials were included in our systematic review and meta-analysis. Partners of trastuzumab included in trials were anthracycline, paclitaxel, docetaxel, anastrozole and letrozole. 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 regimens increased cardiac toxicity (RR=3.37, 95%CI 1.26-9.02) and grade III-IV adverse events. Conclusions: Our study supports the addition of trastuzumab to chemotherapy which is effective and tolerated for metastatic breast cancer with HER2+ patients. Of note, more adverse events will occur followed the use of trastuzumab, especially cardiac toxicity, with two treatment regimens.