RARE-05. MOLECULAR HETEROGENEITY OF PEDIATRIC CHOROID PLEXUS CARCINOMAS

BACKGROUND: Choroid plexus carcinomas (CPCs) are rare aggressive pediatric tumors of the brain with no treatment standards. Genetic profiling of CPCs is often confined to possible association with Li–Fraumenisyndrome, though only about a half of CPCs develop fromsyndromic predispositions. Whole-chromosome gains and losses typical of CPCs reflect genomic instability of these tumors, but only partially explain the aggressive clinical course. METHODS: This retrospective study enrolled 25 pediatric patients with CPC, receiving treatment between January 2009 and June 2022. Molecular genetic testing was performed for 20 cases with available tumor tissue and encompassed mutational status, chromosomal aberrations and gene expression profiles. We analyzed several factors presumably influencing the outcomes, including molecular profiles and clinical parameters. The median follow-up constituted5.2 years (absolute range 2.8–12.6 years). RESULTS: All studied CPCs had smooth mutational profiles with the only recurrent event being TP53 variants, either germline or somatic, encountered in 13 cases. Unbalanced whole-chromosome aberrations, notably multiple monosomies, were highly typical. Inseven tumors, chromosome losses were combined with complex genomic rearrangements: segmental gains and losses or signs of chromothripsis. This phenomenon was associated with extremely low 5-year survival: 20.0±17.9% vs. 85.7±13.2%; p=0.009. Transcriptomically, the cohort split into two polar clusters Ped_CPC1 and Ped_CPC2 differing by survival: 31.3±17.8% vs. 100%; p=0.012. CONCLUSION: CPCs split into at least two molecular subtypes distinguished both genomically and transcriptomically. Clusterization of the tumors into Ped_CPC1 and Ped_CPC2 significantly correlates withsurvival. The distinction may prove relevant in clinical trials for dedicated and patient-oriented optimization of clinical protocols for these rare tumors.