Abstract BACKGROUND Primary central nervous system (CNS) germ cell tumors (GCT) are rare tumors, classified according to histological components and tumor markers (TM) as Germinomas and Non-Germinomatous Germ Cell Tumors (NGGCT). The aim of this study is to assess the outcome of patients with Germinoma and HCGβ levels between 100-200mIU/ml treated according to the Brazilian CNS GCT Consortium Protocol. METHODS From 2013 to 2021, forty-three patients presented with histological and/or TM (serum and CSF) consistent with the diagnosis of germinoma, five of them with HCGβ levels between 100-200mIU/ml. The treatment plan performed was four cycles of carboplatin/etoposide followed by whole ventricular field irradiation (WVFI) of 18Gy with a boost to primary site(s) up to 30Gy and 24Gy craniospinal irradiation (CSI) for disseminated disease. RESULTS Average age 13.7 years (6.3-20.3 years), four males and one female. Diagnosis was made by TM (n=2), and biopsy +TM (n=3). The primary tumor location was pineal (n=2), suprasellar (n=1), and bifocal (n=2) with 1 case presenting ventricular spread at diagnosis. Three patients achieved complete response (CR) after two cycles of chemotherapy and one after four cycles. One patient showed partial radiological response (PR) with negative TM after four cycles and was submitted to a second-look surgery, with pathological report of residual scar tissue. Radiotherapy was performed as described in all patients with four patients receiving WVFI (18Gy+30Gy) and one CSI (24Gy+30Gy). In a mean follow-up of 64 months, overall and event-free survival was 100%. CONCLUSION Despite the small sample, the present study shows effectivity with excellent results and a possibility of increasing the cutoff and therefore reducing treatment for patients with HCGβ at levels up to 200mlU/ml currently treated in some protocols as NGGCT cases.

GCT-10. OUTCOME OF CHILDREN AND ADOLESCENTS DIAGNOSED WITH GERMINOMA WITH HCGΒ VALUES BETWEEN 100-200 MUI/ML TREATED ACCORDING TO THE BRAZILIAN CNS GCT PROTOCOL