LAUSR

e23506 Background: Metastatic osteosarcoma (MOS) with synchronous metastases accounts for 20-25% of all new cases of osteosarcoma. Lungs are the most common site of metastases at presentation (80%) followed by Bone (10%). 5- years Overall Survival (OS) of MOS ranges from 11 to 40%. In a previous study from our institution (Bacci G 2006) on 57 pts < 40 years old (1995-2000) the 2- and 5-year OS were 55% and 18%. Methods: Data of patients with pathologic and radiologic confirmed MOS with adequate follow up were reviewed (EC Approval N 916/2020/Oss/IOR). Time-to-event outcomes were estimate with Kaplan-Meier method and compared between groups with log-rank test and Cox model. Results: From August 2000 to October 2018, 92 patients had a diagnosis of MOS: median age 16.5 yrs (6-73, twelve pts > 40 ), gender rate was M 51/F 41, axial primary tumor in 15 cases, extremity in 77. Lung only metastases were described in 66 (71.7%). In 75/90 cases primary tumor was surgically removed, 43 (46%) cases had at least one surgical metastasectomy. All patients received chemotherapy: preoperative only in 6 cases, postoperative in 6, and pre and postoperative in 66 patients. The 1st line chemotherapy was a combination of drugs: Adriamycin in 91/92 pts, Cisplatin in 89/92, Ifosfamide in 88/92, Methotrexate in 83/92; 59 patients received a 2nd line chemotherapy, 34 pts received a 3rd line; most employed regimen were Gemcitabine-Docetaxel, Ifosfamide 15 gr/m2, Cyclophosphamyde-Etoposide, TKI (Pazopanib, Sorafenib), and a few received experimental drugs. Complete remission (CR) was obtained in 26/92 (28%), in 19 cases after surgical metastasectomy.In 30 pts the information of PGP (P- glycoprotein) was available; patients with positive PGP (19/30) had a worst overall survival as compared to those PGP negative (P = 0.038). Of those in Complete Remission 14/26 relapsed. At December 2020 with a median follow-up of 95 ms (IQR 34-159): 65/92 (70%) died , 12 are alive and free from disease , 6 are alive with disease, 9 were lost . The 2-yrs OS for all 92 pts from diagnosis was 66% (95%CI 55-75) and 5-yrs OS was 26% (95% CI 16-37). From the end of treatment, for those who reached a CR the 5-year OS was 57% vs 9% for those who did not (P < 0.001). At univariate analysis, primary tumor site (2-y OS 48% axial vs 72% extremity, P < 0.001), site of metastases (2-y OS 74% only lung vs 48% other, P = 0.004) and number of lung nodules (P = 0.007), were significantly associated to OS. At multivariate analysis, only site of metastases (other vs. only lung HR = 2.26, 95%CI: 1.21-4.22) and number of lung nodules (≥10 nodules vs ≤3 HR = 2.44, 95%CI: 1.24-4.81) were confirmed as significant for OS. Conclusions: Compared to our previous report from 20 yrs ago, 2-years and 5 yrs OS of MOS has improved but it remain unsatisfactory (66% vs 55% and 26% vs 18%).