Purpose: To present long-term results adjuvant neutron therapy in combined modality treatment of patients with primary-metastatic breast cancer. Material and methods: The studied included 53 patients with stage T2-4N1-3M1 breast cancer, who underwent multimodality treatment: neoadjuvant chemotherapy (NACT) and adjuvant chemotherapy (ACT) according to CMF, CAF/FAC schemes, antiestrogen therapy (if indicated), radical mastectomy (RM) and radiotherapy using different types of ionizing radiation, from 2007 to 2018. All patients were divided into two groups. Group I patients (n = 23) underwent neutron therapy delivered to the anterior chest and group II patients (n = 30) received photon therapy. Results: The 6-year disease-free survival rate was 93.7 ± 6.1 % in patients who received adjuvant neutron therapy and 67.8 ± 7.6 % in patients who received photon therapy (p = 0.047). The overall 6-year survival rates in groups I and II were 68.9 ± 7.8 % and 45.9 ± 6.9, respectively (p = 0.36). Neutron therapy was well tolerated by all breast cancer patients. Conclusion: In patients with stage T2-4N1-3M1 breast cancer neutron therapy as a dense ionizing radiation is more effective due to its biological characteristics. Radical surgery combined with chemotherapy is known to improve survival of breast cancer patients