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Background: Primary breast sarcoma PBS is an extremely rare and heterogeneous group of malignancies ith limited publications confined to small retrospective case revies and case reports. Optimal care is poorly defined because information from previous studies is insufficient and inconsistent. Methods: Data ere obtained from the Surveillance, Epidemiology, and End Results Program for the years 19732012 n = 785 . Stringent inclusion criteria ere applied. Analyses of patient, pathologic, and treatment characteristics ere performed to determine clinicopathological characteristics of PBS and estimate their associations ith overall survival OS and cancer-specific survival CSS . Results: Median age of PBS as 50-60 years and median OS as 108 months. Histologically, the main subtype as angiosarcoma n = 252 . Osteosarcoma and fibrosarcomaliposarcoma shoed the orst and the best prognosis, respectively. Aging, multiple breast location involvement, tumor histology, tumor grade and increased tumor spread ere associated ith poor survival outcomes. There as a substantially increased non-cancer death risk after 48 months. We then validated AJCC 7th staging system for soft tissue sarcoma in PBS and found unknon grade of tumor Gx as associated ith significantly orse prognosis, compared ith loer grade of G1G2 adjHR 2xB7;34 [95 percent CI 1xB7;63-3xB7;34] . Mastectomy as associated ith orse survival outcomes compared ith breast conservative surgery BCS adjHR 2xB7;12 [95 percent CI, 1xB7;582xB7;85] in hole M0 patients and in subgroups by tumor size, tumor grade, tumor histology or radiation history. Adjuvant radiation improved survival outcomes in patients ith tumor size 5 cm adjHR 0xB7;63 [95 percent CI, 0xB7;430.91] , but not in patients ith tumor size x2264; 5 cm. Finally, a ne prognostic model using patient and pathological features as developed. Conclusions: There as a substantially increased non-cancer death risk after 48 months. Gx is a poor prognostic factor, compared ith G1G2. Optimal surgical therapy should strive for R0 resection by BCS henever possible. Adjuvant radiation should be considered in patients ith tumor size over 5 cm.,J Clin Oncol 34, 2016 suppl; abstr 11031 00:00.0,Sarcoma