MBRS-61. MOLECULAR SUB-GROUPING OF PEDIATRIC MEDULLOBLASTOMA: CORRELATION WITH CLINICAL AND HISTOLOGICAL FEATURES, A SINGLE INSTITUTIONAL STUDY

INTRODUCTION: Molecular subgroups of pediatric medulloblastomas are distinctive in infantile and non-infantile age-groups. METHODS: Real-time quantitative PCR based GEP of customized 12 protein-coding genes was performed on 206 FFPE childhood medulloblastoma samples. FISH for MYC amplification, monosomy 6 and sequencing for CTNNB1 exon 3 mutation were done in relevant cases. H&E and reticulin-stained slides were used for histological subtyping. p53-protein immunoreactivity pattern was noted. RESULTS: Infantile (n=33) comprised 57.6% SHH-activated (desmoplastic: 73.7%; MBEN: 15.8% and classic: 10.5%), 21.2% group 3 (large cell/anaplastic [LCA]: 28.6% and none were desmoplastic) and 12% group 4. 40% of group 3 patients died of disease and 21% of the SHH-activated (all desmoplastic) had subsequent local recurrence. Non-infantile (n=173) comprised 19.4% WNT-activated, 12.9% SHH-activated (15% classic, 30% desmoplastic, 10% paucinodular), 19.4% group 3 (63.3% classic & 26.7% LCA), 48.4% group 4 (73.3% classic, 5.3% desmoplastic, 10.7% paucinodular & 1.4% LCA), and non-WNT/non-SHH (NWNS), NOS (n=14,9%) and unclassified (n=4,2.6%). None of WNT-activated were desmoplastic/LCA histology. Non-infantile WNT-activated and group 3 MBs showed 90% monosomy 6 & CTNNB1 mutation, and 16.7% MYC-amplification respectively. 17.4% (13% spinal, 4.4% local) WNT-activated, 31% (12.5% local, 18.5% distant [spinal: 12.5%, intracranial:6%]) SHH-activated, 27% (18% both spinal and local, 9% spinal) group 3 and 31.5% (7.4% local, 5.5% intracranial, 11.2% spinal, 7.4% both spinal and local) group 4 showed metastases during follow up. CONCLUSIONS: SHH-activated and group 3 are the common infantile subgroups but group 4 is not non-existent in infantile age. No desmoplastic (including paucinodular) histological subtype is of WNT- activated and group 3.