1203 Extraosseous Ewing's sarcoma and primitive neuroectodermal tumor. A plea for multidisciplinary approach

Abstract

Ewing's sarcomas (ES) and primitive neuroectodertnal tumors (PNET) are both rare small round cell tumors. ES may arise in the soft tissues and is then referred to as extra-osseous Ewing's sarcoma (EOES). Both ES/EOES and PNET have a specific chromosome translocation resulting from reciprocal exchange of material between chromosomes 11 and 22, suggesting an identical cytogenetic event, as evidence that these two tumors are related entities on a common pathway of differentiation. This does not mean that the clinical course and treatment response of PNET and ES are the same. Data on PNET and EOES are rare. From most retrospective studies it is suggested that the prognosis of patients with ES is detertnined by local control of primary site and early suppression of clinical overt or hidden distant metastases. Where local therapy alone resulted in a 5-year survival of 10% only, the introduction of adjuvant chemotherapy in the last two decades has improved longtertn survival to more than 50%. We present our clinical experience with PNET (11×) and EOES (17×) in 28 adolescents and adults, with specific details on the results of different treatment strategies. Two of the 8 patients, primarily metastasized, that started with chemotherapy, followed by various forms of local treatment, are still in complete remission for more than two years. In non-metastasized disease, a combined modality therapy was also the most successful treatment strategy. Single modality treatment (3 patients) resulted in relapse in all, where salvage surgery and radiotherapy could render one patient only into NED for more than 9 years now. Multimodality treatment (chemotherapy, surgery and radiotherapy) alike the Ewing's Sarcoma CESS and EICESS protocol, resulted NED in 6/10 patients, where surgery upfront resulted in NED in 3/7 patients. Also in our data survival among PNET patients was worse than in EOES (36% vs 47%). The overall disease free 5 year survival of EOES and PNET in this study is 41% (12/28 patients), with response to treatment in 25 patients (21 CR, 4 PR). Multidisciplinary treatment seems essential in improving treatment results in these rare tumours. The optimal chemotherapy schedule and timing of local therapies is still to be assessed.