High-sensitivity Approach for Detection of Tert Promoter Variants in Shh-activated Pediatric Medulloblastomas

TERT promoter ( TERT p) hotspot variants − 124C > T (C228T) and − 146C > T (C250T) are recurrent in various central nervous system tumors and serve as established prognostic markers in many cases. Among medulloblastoma molecular subgroups, TERT p variants are most frequently observed in adult SHH-activated (Sonic Hedgehog) medulloblastomas and are traditionally considered mutually exclusive one another. However, their prognostic significance remains unclear and appears to be subgroup-dependent, being associated with improved survival in SHH-activated tumors but poorer outcomes in Group 4 medulloblastomas. We investigated the presence of the C228T and C250T hotspot variants in TERT p using high-sensitivity droplet digital PCR (ddPCR) in ten consecutive pediatric SHH-activated medulloblastomas (nine desmoplastic/nodular and one extensively nodular) with sufficient residual material available for analysis. Both variants were detected in all tumors, with variant allele frequencies (VAFs) ranging from 0.14% to 61.7% for C228T and 0.06% to 44.6% for C250T. Notably, only the two patients aged ≥ 10 years exhibited high VAFs. Additionally, we compared the results of 5 out of our 10 cases, which were also analyzed by Children’s Brain Tumor Network (CBTN; PedcBioPortal) through Whole Genome Sequencing (WGS). In all five cases, the CBTN analyses yielded negative results. In conclusion, our findings indicate that the two TERT p variants may co-occur; they are ubiquitously present at low VAFs in younger children, while higher TERT p variants VAFs increase with patient age. Larger cohorts are required to validate these findings and to elucidate the prognostic significance of TERT p variants at low and high VAFs in SHH-activated medulloblastomas.