Objective. To evaluate the safety of chemotherapy and trastuzumab in combination with radiation therapy for locally advanced HER2-positive breast cancer (BC). Subjects and methods. The investigation enrolled 73 patients with Stage III BC who underwent combined treatment with concurrent chemoradiation therapy. Of these, 37 patients received treatment in conjunction of targeted therapy with trastuzumab and 36 did not take targeted drugs. At Stage 1, all the patients received 4 chemotherapy cycles according to the chemotherapy regimen for BC, followed by the use of docetaxel in combination with radiation therapy with or without trastuzumab. Adverse events were evaluated according to the EORTC/RTOG, LENT/SOMA, and STS АЕ4 scales. Results. Common reactions, such as nausea, alopecia, were observed in 100% of cases in both groups. There were no differences in the hematologic toxicity profile. Special attention is paid to the absence of severe cardiotoxicity; the development of severe complications, primarily heart failure, was not seen in any of the groups. Late radiation injuries of the skin were more common in 23 (62%) patients in the trastuzumab group and in 18 (50%) patients in the non-trastuzumab group. Conclusion. The investigation shows that concurrent chemoradiotherapy in combination with targeted therapy can yield good results with acceptable toxicity.