Efficacy of dose intensification in induction therapy for localized Ewing sarcoma: Italian Sarcoma Group (ISG) and Associazione Italiana Ematologia ed Oncologia Pediatrica (AIEOP) ISG/AIEOP EW-1 study

11501 Background: The role of dose intensification of chemotherapy in Ewing sarcoma (ES) is under evaluation in prospective trials. This is a controlled, randomized phase III study evaluating the impact on event-free survival (EFS) of two arms at different intensity of induction therapy in localized ES at onset. Methods: Newly diagnosed localized ES patients aged 2-40 were eligible. They were randomized to receive 4-courses induction therapy - 1 every 21 days - either with a standard arm (arm A) as per ISG/SSGIII protocol (Ferrari S, et at, Ann Oncol. 2011;22(5):1221) or with an intense arm B, consisting of vincristine 1,5mg/sqm+ doxorubicin 80mg/sqm+ifosfamide 9g/sqm for each course. After induction, patients underwent surgery and/or radiotherapy,followed by an adaptive treatment. Good responders received standard courses chemotherapy: arm A pts received 9 courses, while arm B pts received 5 courses. Poor responders in both arms received 4 courses followed by high-dose busulfan/melphalan+autologous stem cell rescue. The primary outcome measure was EFS for the 2 arms in the intention-to-treat population. Kaplan-Meier curves compared with log-rank test and Cox model were performed to assess differences between study arms. A secondary outcome was toxicity differences, assessed by means of the Fisher’s exact test. Initial sample size was 230 pts, type I error rate 5%, power 80%. Results: Between 2009 and 2019, 234 patients were randomized (arm A-115; arm B-119). M:F ratio was 1.8; median age 14 years (range 2-40); tumour site extremity in 55%, axial/pelvis in 45%; tumour volume < 200ml in 31% and ≥200ml in 69%. A good response was obtained in 56% in arm A and 60% in arm B. Median follow-up was 68 months. EFS was not significantly different between arms; HR: 0.85; 95% CI: 0,51-1,41, 5-year EFS (95% CI) was 73% (64-82%) in arm A and 75% (67-83%) in arm B ( p = 0.526). Good responders in arm A and in arm B and poor responders in arm B had comparable results: 5-year EFS (95% CI) was 80% (71-91%), 77% (67-88%), and 72% (59-86%), respectively, while poor responders in arm A showed a worse, not statistically significant (p = 0.164) performance (63%; 50-78%). Subgroup analyses showed similar outcome for age, tumour site and volume in both arms. Hematological, gastrointestinal, and cardiovascular grade ≥3 toxicities were more pronounced in arm B (p < 0.05). Conclusions: Intense induction therapy with arm B did not improve 5-year EFS when compared with the standard arm A. The higher toxicity observed in arm B than in arm A was counterbalanced, in good responders, by a similar outcome with a shorter treatment plan. For poor responders, with almost 30 patients per arm event-free and with < 48-month FUP, better 5-year EFS in arm B than in arm A was observed but needs further observation. Clinical trial information: NCT02063022.