Abstract 3561: Recurrent genetic alterations in epigenetic pineoblastoma subtypes
Authors: Goschzik Tobias , Yuan Mathias , Mynarek Martin , Pfaff Elke , Dörner Evelyn , Jones David T. , Pfister Stefan M. , Rutkowski Stefan , Pietsch Torsten 
Published: April 2023

Abstract
Introduction: Genome-wide methylation analyses recently revealed novel epigenetic pineoblastoma (PBL) subtypes, but so far few data are available on recurrent cytogenetic alterations due to the rarity of these neoplasms. Therefore, our aim was to shed further light onto the molecular and genetic characteristics underlying the pathogenesis of pineoblastoma subtypes.
Experimental procedures: Cytogenetic alterations of tumor samples of 60 patients with a diagnosis of PBL confirmed by reference neuropathology and methylation array profiling (450K or EPIC BeadChips (Illumina)) were analyzed by high-resolution genome-wide molecular inversion probe analysis. 52 cases could be screened for mutations by next-generation DNA panel sequencing. Survival data of 41 patients were available. All patients had surgery and older patients (≥4y) received RT followed by maintenance chemotherapy (n=37); infants (&lt;4y) were primarily given a RT-sparing regimen that involved intensified chemotherapy dosage.
Results: Of the recently published epigenetic consensus PBL subtypes (Liu et al., 2021), our cohort consisted of 37 PBL-miRNA1 (1A, 30; 1B, 7), 17 PBL-miRNA2, 2 PBL-MYC/FOXR2, and 4 PBL-RB1 samples. PBL-miRNA subtype tumors had characteristic alterations in microRNA-processing genes; DICER1 mutations (n=14; 4 in Grp1A/1 in Grp1B/9 in Grp2) were most abundant, followed by homozygous deletions of the DROSHA locus (n=11; 8/1/2) and DROSHA mutations (n=9; 3/3/3). Most frequent cytogenetic aberrations in these subtypes were chromosome (chr.) 7 gains (n=25) and chr. 14 losses (n=20, with all but one of miRNA2 cases). DICER1 mutations were significantly associated with chr. 14 losses (p&lt;0.001). 17 cases showed gains of the chromosomal arm 14q, in 6 additional cases, focal gains were found of the OTX2 oncogene located on chr. 14q. In the miRNA subtypes we identified cases with a tetraploid phenotype (n=11; 7/4/0). Interestingly, none of the 6 patients with tetraploid tumors and survival data had relapses, while the remaining patients of the miRNA subtypes had a 5-year PFS of 72% and 5-year OS of 68% (10 of 31 with relapse/death) after a median follow-up time of 3.9 years. However, this did not reach statistical significance. A significant impact on survival could not be demonstrated for chr. 14q gains or focal OTX2 gains. The PBL-RB1 subtype cases had homozygous RB1 deletions (n=3) or biallelic RB1 mutations (n=1). Focal chromosomal aberrations were frequently found in this subtype, but rarely numerical alterations.
Conclusion: The epigenetically defined PBL subtypes were characterized by distinct cytogenetic and mutational events. Although we could not demonstrate a prognostic impact of these events, this might be due to the small sample size. A possible prognostic role for a superior (e.g. tetraploidy) or inferior outcome (e.g. OTX2 gains) need studies in larger cohorts and ideally in prospective clinical trials.
Citation Format: Tobias Goschzik, Mathias Yuan, Martin Mynarek, Elke Pfaff, Evelyn Dörner, David T. Jones, Stefan M. Pfister, Stefan Rutkowski, Torsten Pietsch. Recurrent genetic alterations in epigenetic pineoblastoma subtypes. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3561.