11046 Background: Angiosarcoma of bone (B-AS) is an exceedingly rare malignant tumor of vascular origin. The aim of this EMSOS retrospective study is to report on natural history, type of treatment and prognosis of B-AS. Methods: Patient data were collected according to the national rules for observational studies through electronic dataset available on EMSOS WEBsite. Results: 80 patients (51 male and 29 female, median age 54 years, range 17 to 92 years, 56% with localized disease, 44% metastatic) from 8 EMSOS Centers were collected. Surgery of the primary tumor was performed in 76% of patients (amputation in 30%), with intralesional margins in 26%. A surgical complete remission status (SCR) was achieved in 47% of the patients. Radiotherapy (RT) was delivered in 41% of the patients (in 15 patients as definitive local treatment), chemotherapy (CT) in 47% (56% in metastatic and 41% in localized cases). With a median follow-up of 31 months (range 40 to 309 months), 68% of patients died, 16% were disease-free, 12% were alive with disease and 4% dead for other causes. The 5-year overall survival (OS) was 27% (95%CI 16-30): 41% (95%CI 25-56) for localized patients (45% SCR, 17% no SCR, p = 0.03) and 8% (95%CI 0-20) for metastatic patients (p = 0.002). Among metastatic patients, 29/35 have died, with a median time to death of 6 months (1-45), while 6 patients were alive with a median follow-up of 22 months (8-106). Improved survival was observed for male patients (30% vs 8%, p = 0.04), while type of treatment (surgery, chemotherapy, radiation), pattern of metastases and age did not affect outcome. In 18 metastatic patients who underwent chemotherapy partial respo nse (PR) was documented in 1/3 patients after paclitaxel (RR 33%), and stable disease (SD) in 5 patients (2/2 with gemcitabine, 2/8 with doxorubicin/ifosfamide, and 1/4 with osteosarcoma-like chemotherapy). In localized patients, the 5-year OS was significantly better for age ≤ 50 years (68% vs 34%, p = 0.02) and extremity and central tumor as compared with pelvis/sacral location (50% vs 58% vs 0%, p = 0.008), with improved disease-free survival (DFS) after chemotherapy (49% vs 33%, p = 0.04). Conclusions: Metastatic B-AS is a fatal disease and inclusion in experimental trials is warranted. In localized patients, a better probability of survival is expected in younger and surgically treated patients. The use of chemotherapy was associated with improved DFS.