Primary Mediastinal Ewing's Sarcoma: Post Hoc Analysis from Two International Multicenter Prospective Randomized Trials.

Objective: Ewing sarcoma (EWS) of the mediastinum is extremely rare, with only a few cases reported in the literature. We aimed to gain a better understanding of primary mediastinal EWS, describing patients treated within two international, multicenter, prospective, randomized EWS trials.

Methods: Data from patients with primary mediastinal EWS were retrieved from the database of the EURO-E.W.I.N.G.99 (ClinicalTrials.gov identifier: NCT00020566) and EWING 2008 (ClinicalTrials.gov identifier: NCT00987636) trials. Patient and treatment characteristics were analyzed.

Results: Out of 2969 patients with EWS, 9 (0.3%) had primary mediastinal EWS. The median age at diagnosis was 30.5 years (4 to 49). At the time of diagnosis, = 3 (33%) patients had synchronous metastases. All patients underwent multiagent chemotherapy. Local therapy for non-metastatic patients was surgery ( = 2, 22%), surgery and radiotherapy ( = 2, 22%) or radiotherapy alone ( = 2, 22%). Surgery consisted of extended resections in most patients ( = 3, 33%). Five-year survival for the whole cohort was 64%. Apart from one patient who was lost to follow-up, all patients ( = 4) who had undergone surgery were alive at the end of follow-up.

Conclusions: Primary mediastinal ES is extremely rare, with a prevalence of 0.3% among EWS. Five-year survival was favorable compared to primary mediastinal sarcoma of all histologies and in line with EWS of different origin.