LINC-05. PRIMARY CENTRAL NERVOUS SYSTEM EWING SARCOMA IN PEDIATRIC AND AYA PATIENTS: 2 INSTITUTIONS EXPERIENCE IN BUENOS AIRES ARGENTINA

INTRODUCTION: Ewing Sarcoma (ES) is defined by molecular markers, being t(11;22)(q24;q12) the most frequent. Intracranial ES usually shows as metastases from extracranial sites. Primary central nervous system (CNS) lesions are extremely rare. MATERIAL AND METHODS: Retrospective review of clinical records from patients with primary CNS ES, assessed at 2 institutions in Argentina between 2007–2019. Translocation was evidenced in all cases through molecular testing. Clinical characteristics, imaging, histopathology, and treatment response were evaluated. Extracranial and osseous lesions were excluded. RESULTS: 15 patients. Median age at beginning of symptoms: 8 yo (2–20). Most patients had intracranial hypertension syndrome (14/15). In brain MRI, 5/15 supratentorial lesions, 4/15 posterior fosa, 1/15 medullary, 2/15 supra and infratentorial, and 3/15 lesions diffuse leptomeningeal infiltration. Histopathologic findings showed diffuse pattern with small round blue cells in most cases, other patterns were also described. CD99 marked positive in all cases. Misdiagnosis with glial tumors (4/15), medulloblastoma (6/15) and infectious diseases (3/15); led to median delay to accurate diagnosis of 3 months (range 0–67). After correct diagnosis patients were treated with standard ES treatment (6 VIDE cycles plus radiotherapy) in 14/15 patients. Vincristine, irinotecan and temozolamide was used as second line treatment in all relapse cases whenever possible. EFS was 22 months (2- 65). OS at 5 years of follow-up was 46,67% (mean OS 31 mo). CONCLUSION: Even though molecular assessment led to accurate diagnosis in all cases, treatment response and outcome showed two different groups of patients with long and very short survival. Adaptative therapy should be considered.