Outcomes of Methotrexate-Based Therapy for Paediatric Osteosarcoma: A Decade of Experience from a Cancer Centre in Pakistan.

Introduction: Osteosarcoma is the most common bone malignancy in children. We describe the survival outcomes of children diagnosed with osteosarcoma at a tertiary care cancer centre in Pakistan treated with a methotrexate-based treatment regimen. Materials and Methods: This was a retrospective review of electronic medical records at our institute for patients diagnosed with osteosarcoma between January 1st, 2011, to December 31st, 2020. Kaplan Meier curves were generated. Overall survival (OS) was defined as the time from diagnosis to death or last follow up. Event-free survival (EFS) was defined as time from diagnosis to death, progression, relapse, treatment abandonment, or last follow up. Results: We identified 372 medical charts, of which 35 were excluded (34 abandoned prior to therapy, 1 chondrosarcoma), leaving 337 records for analysis. Median age was 13.8 years (range 2.4 - 17.9 years). At baseline, 295 patients (87.5%) had localized disease, and the lower extremity was the most common primary tumour site (286, 84.9%). The median follow-up time was 55 months (range, 1-149 months), during which 100 deaths were observed (75 attributed to disease progression, 18 infection-related, 7 due to cardiotoxicity), while 42 (12.5%) patients abandoned active treatment. The median overall survival was not reached. The estimated 3-year, 5-year, and 10-year overall survival rates with 95% confidence intervals were 72% (67 - 78%), 65% (59 - 71%), and 55% (44 - 69%), respectively. The median EFS was 26.6 months. The estimated 3-year, 5-year, and 10-year EFS rates with 95% CI were 43% (39 - 49%), 40% (35 - 46%), and 25% (16 - 40%), respectively. Conclusion: Survival outcomes for localized osteosarcoma with a methotrexate-based treatment regimen are near regional estimates but reflect a high rate of infection-related mortality, treatment abandonment, and amputations.