MBCL-05. TREATMENT OF CHILDREN WITH MEDULLOBLASTOMA WITHOUT METASTATIC INVOLVEMENT IN THE AGE GROUP OLDER THAN 3 YEARS: RESULTS OF INTERCENTER TRIAL

The aim of this study was to identify a group of patients aged 3 to 7 years for whom there is the possibility for reducing of craniospinal radiation dose (CSI). From 2008 to 2018 fifty one pediatric patients with primary diagnosed medulloblastoma in the age group 3 - 18 years were included in trial, 38 in standard risk group, 13 in high risk group. Treatment program consisted of surgical removal of the primary tumor site with subsequent radiation therapy (with CSI of 23,4 Gy or 36 Gy, depending on the risk group) and high-dose chemotherapy (with high-dose cyclophosphamide or thiophosphamide). As a result of this study, sufficiently high rates of overall survival and progression/relapse - free survival (PFS) were achieved in standard and high-risk groups patients, which amounted to 76,0 ± 8,8% and 83,3 ± 10,8% with median follow-up 62,9 ± 6,2 months and 52,2 ± 7,8 months, respectively. There was revealed patients group in the age 3 - 7 years with 100% PFS and median follow-up 66,9 ± 8,9 months. Morphological and molecular biological factors of an unfavorable outcome of the disease (large cell - anaplastic histology, MYC/MYC-N gene amplification, Iso17q and TP53 gene mutation) were absent in this tumor samples. We have also achieved 100% PFS in patients with desmoplastic tumor histology and in patients, who were treated with thiphosphamide - based chemotherapy regimen. Molecular - biological characteristics analysis of tumor cells showed a negative effect on PFS of DNMT - positive status (Score 4 and>, by 3 markers) and presence of MYC-N gene amplification (SHH molecular subgroup).