Comparative Outcome of Thai Pediatric Osteosarcoma Treated with Two Protocols: the Role of High-Dose Methotrexate (HDMTX) in a Single Institute Experience

Background: High-dose methotrexate (HD-MTX) is recognized as an efficient component of therapy againstpediatric osteosarcoma in combination with other drugs such as cisplatin (CDP), carboplatin (CBDCA),doxorubicin (ADM), etoposide (VP-16) and ifosfamide (IFO).
Objectives: To demonstrate the feasibility andeffectiveness of the HD-MTX/CDP/DOX/VP-16/IFO [MTX(+)] protocol comparable to CDP/ADM/CBDCA/IFO[MTX(-)] for treating childhood osteosarcoma at Ramathibodi Hospital (1999-2014). Materials and
Methods:A retrospective analysis was conducted of osteosarcoma patients aged less than 18 years treated with twochemotherapeutic regimens between 1999 and 2014. A total of 45 patients received the MTX(-) and 21 the MTX(+)protocol.
Results: Overall limb-salvage and amputation rate were 12.9% and 77.7%, respectively. Kaplan-Meier analysis results for 3-year disease free survival (DFS) and overall survival (OS) regardless of treatmentregimens were 43.4±6.0% and 53.2±6.1% respectively. The 3-year DFS and OS were improved significantlywith the MTX(+) protocol compared to MTX(-) protocol (p=0.010 and p=0.009, log rank test) [69.8±10.5%,79.8±9.1% for MTX(+) and 31.1±6.9%, 42.2±7.4% for MTX(-) protocol, respectively]. Patients with metastaticosteosarcoma treated with the MTX(+) protocol had statistically significant higher 3-year DFS and OS thanthose treated with the MTX(-) protocol (66.7±13.6% and 15.0±8.0% for 3-year DFS, p=0.010, 73.3±13.2% and20±8.9% for 3-year OS, p=0.006, respectively). The independent risk factors for having inferior 3-year DFSand OS were poor histological response (tumor necrosis <90%) and treatment with the MTX(-) protocol. Themultivariate analysis identified only the treatment with the MTX(-) protocol as an independent predictor ofinferior OS with a hazard ratio (HR) of 3.53 (95% confidence interval of 1.2-10.41, p=0.022).
Conclusions: Ourstudy demonstrated the tolerability, feasibility and efficacy of the HDMTX-based regimen improving the survivalrate in pediatric osteosarcoma cases, in line with reports from developed countries.