Background. In this prospective analysis, we aimed to characterize the treatment opinions on male breast cancer (MBC). Patients and methods. In this prospective cohort study we included patients treated between May2009 and June 2018 for MBC. Results. The median follow-up was 30 months (range 2-84 months) and the median age at diagnosis was 69 years (range 27-96 years). Radical mastectomy was performed in 354 (96.2%) cases. Most (n=194, 52.9%) patients underwent sentinel-node biopsy (SNB). However, the vast majority of patients with clinical and sonographic suspicious axillary lymph nodes (n=72, 81.8%) underwent ALND. Adjuvant radiation of chest wall post mastectomy or of the breast post breast conserving surgery was performed in 193 (51.9%) patients. Systemic therapy was administered to 155 (41.0%) patients, and was administered predominantly in the adjuvant setting. Most common was anthracycline-taxane-based therapy. Of patients with HER2 (n=43) overexpressing tumors, 29 (67.4%) received trastuzumab. Adjuvant endocrine therapy was administered to 92.3% of patients, predominantly tamoxifen. Important decision criteria for adjuvant radiation and chemotherapy were advanced stage of disease, lymph node metastases, undifferentiated tumors, lymph- and blood vessel invasion. During the follow up period 609 cycles of chemotherapy were administered (median 6 cycles per person). Haematological and non-haematological toxic effects were observed in 68 (16.4%) and 57 (53.3%) patients, respectively. Grade 3 and 4 haematological events were rare. The most common was neutropenia in 17 (15.8%) and febrile neutropenia in 10 (9.3%) cases. Nausea and vomiting were the most commonly observed grade 3 and 4 non-haematological adverse events observed in 7 (4.6%) cases. Endocrine therapy was discontinued in 53 (16.2%) patients and chemotherapy in 25 (16.1%) cases. Conclusions. In this large prospective study, we found that MBC is treated according to current guidelines and treatment seems to be not inferior in comparison with that treatment of FBC. Citation Format: Holm Eggemann, Cosima Brucker, Susen Schirrmeister, Uta Ringsdorf, Doris Augustin, Michael Schrauder, Marc Thill, Felix Flock, Susanne Kraudelt, Gabriele Gad, Anke Kleine-Tebbe, Mattea Reinisch, Serban- Dan Costa, Atanas Ignatov. Treatment strategies in male breast cancer: Results of a prospective multicenter study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-17-06.