Multidisciplinary treatment of 99 adult osteosarcoma (OST) patients (pts) with synchronous and metachronous metastases (mets): A retrospective series of the French Sarcoma Group (FSG).

11030 Background: Treatment (trt) options for metastatic OST are scarce. Following failure of standard 1st line therapy pts who relapse present a challenging trt dilemma, and have poor prognosis. Surgical removal of all mets is essential. Currently, there are no standardized 2nd line trt options in relapsed OST. Methods: Pts were identified from 2 sarcoma databases; Netsarc and ConticaBase. Clinical data prospectively registered in the databases were supplemented with retrospective review of the medical records. Results: From January 2009 to December 2016, we identified 99 pts, in 12 FSG centers; 30 with synchronous (SC) and 69 with metachronous (MC) mets, with 62 males. Median age was 25 years (18-53). Total number of mets was 1 for 31 pts, 2-5 for 26 and > 5 for 42. Mets sites were lung, bone and other in 77, 14 and 22 pts respectively. Median time to first MC mets was 22 months (mo) (4-97). All pts except 10 with MC mets received a 1st line systemic trt for relapse, 65 a 2d-line, 38 a 3d-line, and 20 a 4th line, with 27 pts included in a clinical trial. Sixty five pts had local trt of distant mets (surgery for 54, irradiation for 5 and radioablation for 6). Eighteen pts had repeated thoracotomies (2 for 13 pts, 3 for 5, 1 for 1 pt). Nine of 10 MC mets pts (with ≤ 5mets) who never received any systemic trt had complete mets resection, 1 had mets radioablation, all were alive at last follow-up (FU). Median FU was 16.5 mo (2-132). Median progression free survival (PFS) and overall survival (OS) were 5.5 (95%CI 4-7) and 16.5 mo (95%CI 10-25) respectively. In multivariate analysis; > 5 mets, time to 1st mets < 24 mo, were negative prognostic factors on OS and PFS (p= 0.03, 0.01 and p=0.013, 0.00 respectively). Bone mets and absence of mets surgery were negative prognostic factors on OS only (with p=0.012, 0.008). Conclusions: Adult OST pts with distant mets are heterogeneous with poor prognosis. Complete surgery of distant mets remains essential. In reference sarcoma center, OST pts at relapse with > 1 mets commonly receive >1st line of systemic trt, and are included in clinical trial. Multidisciplinary trt combining complete mets local trt and systemic therapy seems to be rational.