Background: DDCS is a rare bone tumor with a poor prognosis. While no standard therapy exists, NCCN guidelines recommend osteosarcoma regimens (ORs). Methods: We performed a retrospective review (January 1, 2007-June 1, 2018) at three sarcoma centers and identified 46 patients (pts) with DDCS to evaluate treatments and outcomes. Results: Median age was 62.5 years (23-83); 61% were male. Median tumor size was 10.5cm (2-34). Most pts had localized disease at diagnosis (dx) (80%), extremity primary (76%), and did not receive neo/adjuvant chemotherapy (70%) or radiotherapy (69%). Local and distant recurrences were frequent (35% and 57%, respectively) and rapid (6.6 months (m) and 5.4 m, respectively). Twenty-eight pts received chemotherapy, 9 neo/adjuvant and 19 for metastasis (met) (Table). Response rate to first line ORs was poor (53% progressed). Notably, 11% had a partial response (D/I). Tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (ICIs) led to stable disease. Median overall survival was 22.8 m and 7.2 m; 5-year survival rates were 30% and 0% in localized and metastatic disease, respectively. Median follow-up was 12.5 m (1.4-120). A multivariate cox proportional hazards model (age, sex, location, met at dx) identified met at dx as the only risk factor for worse prognosis (HR 2.8, p=0.026). Conclusions: DDCS is an aggressive malignancy with a poor prognosis. Despite guidelines to treat with ORs, the benefit is unclear, illustrating the need for randomized trials comparing standard regimens to novel agents.

*2 pts received 2 neo/adjuvant regimens. **In metastatic disease, pts received multiple regimens. Doxorubicin (D), Cisplatin (C), Methotrexate (M), Carboplatin (Ca), Ifosfamide (I), Olaratumab (O), Gemcitabine (G), Docetaxel (T), Etoposide (E), Pazopanib (P), Regorafenib (R), Ipilimumab (Ip), Nivolumab (N), Pembrolizumab (Pe).