Introduction: With the development and widely use of HER2 targeted therapies, HER2 expressing metastatic breast cancer have no longer dismal prognosis as once expected. The combination of HER2 targeted therapies with chemotherapatic agents prolongs overall survival. Pertuzumab is a new monoclonal antibody molecule that binds to the extracellular portion of HER2 and works by inhibiting homoand heterodimerization. The aim of this study is to document the real life data of toxicities seen in metastatic breast cancer patients treated with first line trastuzumab-pertuzumab combination therapy. Material and method: A retrospective review of 26 cases from the medical oncology patient registry was conducted to include the dates October 2016 through December 2017. The number of cycles of treatment and doses, adverse events, dose changes and course delays, reasons for treatment change and types of second line treatments are noted. The imaging and laboratory test results were obtained from the electronic registration system. The cumulative toxicity incidence was accepted as the primary endpoint. Results: The median age of the 26 cases was 54 years. The median cycle number of pertuzumab and docetaxel treatments were 9 and 7, respectively and the median duration of pertuzumab therapy was 6.75 months. As of the date of last follow-up, 80.7% of the cases were still under treatment. There was a total of 6 cases of delay in treatment, of which five were due to neutropenia, while in one case the cause was diarrhea. When the adverse events were examined, at least one side effect (excluding alopecia) was observed in 16 patients and 7 cases had no toxicity except alopecia. In terms of constitutional symptoms, eight of the 19 patients had grade 1 fatique, one case had itching, and three patients had asthenia. Hematologic toxicity was seen in twelve cases and all had at least grade 1 leukopenia. Grade 3-4 febrile neutropenia occurred only in one case. Left ventriculer ejection fraction was measured stable for all of the cases, none of them experienced any significant decrease. Conclusion: According to the results of this retrospective analysis, the use of pertuzumab-trastuzumabdocetaxel in the first line treatment of HER2 expressing metastatic breast cancer had good safety profile and had positive clinical results and paralleled with the results of the pivotal study.