Maintenance therapy with oral cyclophosphamide plus celecoxib in patients with metastatic Ewing sarcoma: Results of the Italian Sarcoma Group/AIEOP EW-2 study.

10517 Background: The prognosis of patients with metastatic Ewing sarcoma remains poor. The primary aim of the ISG/AIEOP EW2 Study (EUDRACT# 2009-011197-15) was to evaluate the feasibility and efficacy of maintenance therapy with oral cyclophosphamide plus celecoxib. Methods: From June 1 st 2009 to Nov 22 nd 2019, 112 patients with metastatic Ewing sarcoma at onset entered the ISG/AIEOP EW2 study, consisting of induction chemotherapy, radiotherapy and/or surgery at the site of the primary tumor, a consolidation phase with high-dose busulphan/melphalan + autologous stem cell rescue, whole-lung irradiation (12-15Gy), and a maintenance phase of 180 days with cyclophosphamide 50 mg daily (35 mg/mq daily if age < 14 years) plus celecoxib 400 mg twice daily (250 mg/mq twice daily if age < 14 years). Exclusion criteria from the maintenance phase were disease progression, cardiac or gastro-intestinal comorbidity. For CTCAE v4.0 grade 3-4 toxicities a temporary interruption was planned. Results: Seventy-one patients were eligible and entered the maintenance phase. Median age was 16 years (range 13-41); sites of metastases were lung or single bone (n = 56) and multicentric metastatic spread (n = 15). Sixty-one patients terminated the maintenance phase, 4 patients are still on treatment, 1 patient interrupted the treatment due to auto-immune thrombocytopenia at 4 months, 5 patients were withdrawn throughout maintenance due to disease progression/relapse. The duration of maintenance therapy was 89% of the scheduled days, with a median suspension length of 12 days (range 1-44 days). Causes of temporary suspension were hematological toxicity (19 episodes), infections (12 episodes), gastrointestinal disorders (9 episodes), fluid retention/distal oedema (3 episodes), renal disorders (3 episodes). Median follow-up was 42 months. The 3-year EFS of patients who entered the maintenance phase was 0.79 ± 0.09 for lung or single bone, and 0.19 ± 0.11 for those with multicentric metastatic spread. Conclusions: This schedule of maintenance phase is feasible, despite previous intensive treatment. A longer follow-up is needed to monitor side effects and to evaluate clinical outcome of patients with lung or single bone metastases, while the outcome remains dismal for multicentric metastatic Ewing sarcoma. Clinical trial information: NCT02727387.