CDKN2A Homozygous Deletion Research Articles

Loss of p16 Immunoexpression and Deletions of CDKN2A in the Progression of Extramammary Paget Disease: An Immunohistochemical and Genetic Study of 24 Invasive/Metastatic Cases.

Information regarding the genetic alterations in extramammary Paget disease (EMPD) is scarce. This study investigated the significance of CDKN2A and MTAP alterations in EMPD progression using immunohistochemistry and panel DNA sequencing. In total, 24 invasive/metastatic EMPD cases were included in this study. The immunoexpression of p16 and MTAP in the primary in situ, primary invasive, and metastatic tumor components was evaluated. Panel DNA sequencing was performed for metastatic tumor components in 5 of the 24 cases. Immunoexpression of p16 in the in situ tumor component was at least partially preserved in all 19 tested cases (100%). By contrast, the invasive tumor component was diffusely or partially lost in 18 (81.8%) of 22 tested cases. Regarding the foci of lymph node metastasis, 13 (81.2%) of the 16 patients showed a significant loss of p16 expression. Loss of MTAP immunoexpression was observed less frequently compared with the loss of p16 expression. CDKN2A homozygous deletions were confirmed in all 5 tested cases by sequencing, whereas MTAP deletions were detected in only 2 cases. In conclusion, p16 expression loss and CDKN2A deletions can be frequently seen in invasive/metastatic cases of EMPD.

P16-CD8-Ki67 Triple Algorithm for Prediction of CDKN2A Mutations in Patients with Multiple Primary and Familial Melanoma.

Melanoma, a malignant neuroectodermic tumor originating from the neural crest, presents a growing global public health challenge and is anticipated to become the second most prevalent malignancy in the USA by 2040. The CDKN2A gene, particularly p16INK4a, plays a pivotal role in inhibiting the cell cycle via the cyclin D/CDK2-pRb pathway in certain tumors. In familial melanomas (FM), 40% exhibit CDKN2A mutations affecting p16INK4a, impacting checkpoint G1, and stabilizing p53 expression. This study aims to establish a scoring system using immunohistochemical antibodies, providing a cost-saving approach to classify multiple primary melanomas (MPM) and FM patients based on their mutational status, thus mitigating genetic testing expenses. This retrospective study included 23 patients with MPM and FM, assessing the p16, CD8, and Ki67 immunohistochemical status. Analyses of each parameter and associations between their value intervals and genetic CDKN2A status were conducted. A total score of at least 9 out of 10 points per tumor defined melanomas with homozygous CDKN2A deletions, exhibiting a sensitivity of 100% and specificity of 94.11%. In conclusion, p16, CD8, and Ki67 individually serve as valuable indicators for predicting melanoma evolution. The algorithm, comprising these three immunohistochemical parameters based on their prognostic and evolutionary significance, proves to be a valuable auxiliary diagnostic tool for cost-effective prediction of mutational status in detecting multiple and familial primary melanomas with CDKN2A homozygous deletion.

Prognostic Effect of CDKN2A Homozygous Deletion and Beclin 1 in Isocitrate Dehydrogenase Mutant Glial Tumors

ABSTRACT Background: In the updated World Health Organization Classification of Central Nervous System Tumors, the presence of CDKN2A/2B homozygous deletion is now recognized as the indicative of Grade 4 in isocitrate dehydrogenase (IDH) mutant astrocytomas, and it is associated with a poor prognosis in Grade 4 astrocytomas. Conversely, Beclin 1, a crucial protein in autophagy initiation, exhibits a bidirectional effect on tumor progression and suppression. The objective of this study is to evaluate CDKN2A homozygous deletion in IDH mutant astrocytomas of varying grades, to compare it with microvascular proliferation (MVP) and palisading necrosis, and to analyze the relationship between these findings and Beclin 1 expression, subsequently comparing them with prognosis. Subjects and Methods: CDKN2A homozygous deletion and Beclin 1 expression were analyzed in 32 cases with IDH-mutant diffuse astrocytomas of Grades 2, 3, and 4. Results: CDKN2A homozygous deletion was detected in one of 10 patients with Grade 2 and in 8 of 17 patients with Grade 4. Beclin 1 was positively stained in 2 of Grade 2 astrocytomas, 4 of Grade 3 astrocytomas, and 9 of Grade 4 astrocytomas. While Beclin 1 expression was present in 5 of 9 cases with CDKN2A homozygous deletion, no expression was observed in four cases. Conclusion: In this study, the prognostic significance of CDKN2A homozygous deletion alone was found to be lower compared to the deletion in combination with MVP and/or necrosis. At the same time, Beclin 1 expression was determined to exert no prognostic significance alone, while it was found to exert a poor prognostic effect in combination with CDKN2A homozygous deletion.

380 2021 WHO Grading Scheme Provides Minimal Incremental Improvement in Prognostic Stratification of a Retrospective IDH-Mutant Astrocytoma Cohort Compared to 2016 WHO Grading Scheme

INTRODUCTION: The 2021 WHO Classification of CNS Tumors introduced prognostically relevant molecular alterations (ex. CDKN2A homozygous deletion) into grading criteria for select tumors. METHODS: We retrospectively identified 176 adult IDHmAstro patients with available next-generation sequencing (NGS). All tumors were regraded based on the 2021 and 2016 WHO grading schema using relevant histopathological (mitotic rate, microvascular proliferation, necrosis) and molecular (CDKN2A) features. The prognostic ability of each grading schema was evaluated with Kaplan-Meier and multivariate Cox Regression analyses. RESULTS: The cohort consisted of 76 grade 2 (43.2%), 45 grade 3 (25.6%), and 55 grade 4 (31.3%) IDHmAstro cases using the 2021 grading schema. Only four patients (2%) had a grade change from the 2016 WHO grading scheme - one prior 2016 WHO grade II and three grade III tumors, all regraded to Grade 4 based on present CDKN2A homozygous deletion. When assessed based on both classification schemas, WHO Grade 4/IV tumors were associated with lower OS than Grade 2/II tumors (HR [95% CI]: 4.20 [1.09–16.22], P = 0.037 per 2016 and 3.82 [1.04–14.09], P = 0.044 per 2021). There were no significant differences in OS between Grade 2/II and Grade 3/III tumors or Grade 3/III and Grade 4/IV tumors within either grading schema. CONCLUSIONS: Only four patients had a change in grade, implying the majority of IDHmAstro patients would have received similar treatment using either grading schema. Interestingly, outcomes for grade 3/III IDHmAstro were not significantly different from grade 2/II or grade 4/IV IDHmAstro in either schema, suggesting that grade 3/III tumors represent a biologically heterogeneous group. These results should be validated in other series but underscore a continued unmet need for novel biomarkers to improve IDHmAstro risk-stratification.

1242 Metabologenomic Characterization Uncovers Heterogeneity Amongst IDH Mutant Gliomas

INTRODUCTION: Mutations in isocitrate dehydrogenase (IDH) enzymes are recognised to drive the molecular footprint of diffuse gliomas through the accumulation of oncometabolite R-2-hydroxyglutarate which drives the widespread restructuring of the DNA methylome; however, beyond R-2-hydroxyglutarate, a comprehensive metabologenomic characterization of IDH-mutant gliomas has yet to be performed. METHODS: Glioma samples from a cohort of 154 patients underwent multiplatform molecular analysis, including metabolomic studies, genome-wide DNA methylation profiling and bulk RNA sequencing. A integrative analysis was performed, including hierarchical clustering and principal component analysis of identified metabolites, differentially methylated probes, copy number alteration and bulk mRNA data. Survival analysis as well as multivariable hazard ratios for clinical variables were calculated by fitting Cox Proportional Hazards Models. RESULTS: We discovered a group of IDH-mutant gliomas whose metabolic profile highly resembled IDH wildtype tumors. Notably, these IDH-mutant gliomas with dysregulated metabolism were distinguished from their IDH-mutant counterparts by significantly shorter overall survival (median OS 118.9 months vs 173.6 months, p=0.048). The IDH-mutant tumors with dysregulated metabolism harbored distinct epigenetic alterations that converged to drive proliferative and stem-like transcriptional profiles. The prognostic relevance of dysregulated metabolism complements, but was not wholly explained by canonically recognized prognostic classifications in IDH-mutant gliomas including 1p/19q codeletion, glioma CpG Island Hypermethylator (GCIMP) status and CDKN2A homozygous deletion. CONCLUSIONS: Utilizing a cross-platform analysis we have uncovered a novel subtyping of IDH-mutant gliomas with dysregulated cellular metabolism with similar survival to IDH-wildtype tumors. The metabolic profile provides unique information on glioma phenotypes, which may facilitate a more comprehensive understanding of glioma biology, and provide a window to target novel dependencies.

Abstract 4598: Discovery of novel MTA-cooperative PRMT5 inhibitors as targeted therapeutics for MTAP-deleted cancers

Abstract Homozygous deletions of the p16/CDKN2a (cyclin dependent kinase inhibitor 2A) locus, which is responsible for regulating the cell cycle, are commonly found in cancer and often involve the deletion of adjacent genes. One such adjacent gene is methylthioadenosine phosphorylase (MTAP), involved in metabolism, located on chromosome 9p21 in close proximity to the p16/CDKN2A tumor-suppressor locus. Co-deletion of MTAP is observed in approximately 80-90% of tumors with homozygous deletion of CDKN2A, representing 10-15% of all human tumors. These tumor types, including non-small cell lung cancer, pancreatic adenocarcinoma, glioblastoma, and mesothelioma, have a poor prognosis, highlighting the significant unmet medical need in this area. Deletion of MTAP leads to a significant accumulation of methylthioadenosine (MTA) in cells. MTA, at high concentrations, selectively inhibits the PRMT5 methyltransferase enzyme, competing with the substrate S-adenosylmethionine (SAM) required for methylation reactions. As a result, the overall level of symmetric arginine dimethylation throughout the proteome is reduced. This heightened sensitivity to modulation of methylosome activity makes cells with MTAP deletion more susceptible to therapeutic targeting of PRMT5. Hence, selective targeting of PRMT5 in cancers with homozygous MTAP deletion represents a promising strategy for specifically eliminating cancer cells with this genetic alteration. Ryvu has developed MTA-cooperative PRMT5 inhibitors characterized by good drug-like physicochemical properties and inhibition of methyltransferase activity with IC50 values in the low nanomolar range. A structure-based lead optimization delivered compounds coming from two independent series with high selective potency in MTAP-deleted cell lines and DMPK profiles allowing an oral administration. The antitumor activities were compared in vitro and in vivo to MRTX1719 and AMG193 in MTAP null tumors such as HCT116 MTAP KO, DoHH-2 and Lu99. The correlation between compound exposure and on-target effect was confirmed in PK/PD and efficacy studies. Taken together, these studies confirm that MTA cooperative PRMT5 inhibitors exert strong synthetic lethal phenotype in MTAP deleted cancers and offer an exciting therapeutic opportunity for a large patient population. Citation Format: Adam Radzimierski, Aneta Bobowska, Agata Stachowicz, Kamil Kuś, Kamila Kozłowska-Tomczyk, Agnieszka Ludwig-Słomczyńska, Paulina Podkalicka-Gołda, Aniela Gołas, Monika Żukowska, Pavlo Lebed, Przemysław Wyrębek, Daria Szukiel, Matylda Stefaniak, Oleksandr Popika, Julia Krzywik, Sujit Sasmal, Paulina Niedziejko-Ćwiertnia, Klara Korta-Piątek, Karolina Fijołkowska, Aleksandra Więckowska, Marta Olszak-Płachta, Swapnil Nipunge, Mateusz Świrski, Marek Wronowski, Henryk Pawlik, Quỳnh Vũ, Katarzyna Łagosz-Ćwik, Mateusz Stoszko, Szymon Woroszyło, Igor Tomczyk, Ewelina Gabor-Worwa, Nilesh Gaud, Anna Kowal-Chwast, Dawid Gogola, Magdalena Miodek, Róża Starczak, Agata Dudek, Jacek Faber, Bożena Winnik, Sanja Novak-Ratajczak, Agnieszka Świrska, Karolina Gluza, Paweł Guzik, Katarzyna Banaszak, Nicolas Boutard, Grzegorz Ćwiertnia, Krzysztof Brzózka, Mateusz Nowak, Anna Bartosik, Didier Pez. Discovery of novel MTA-cooperative PRMT5 inhibitors as targeted therapeutics for MTAP-deleted cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4598.

Abstract 7407: Melanoma clonal subline analysis reveals genetic factors driving intra-tumor heterogeneity

Abstract Melanoma is the most invasive skin cancer caused by the malignant melanocytes. The use of immune checkpoint blockade (ICB) improved the survival rate in advanced melanoma. Yet, the response rate to ICB varies across patients due to the highly heterogeneous nature of melanoma. Recent studies reported genomic and epigenetic factors contributing to the therapeutic response. Identifying these factors involved in clonal evolution in melanoma is a key to better understanding the tumor progression and divergence in the therapy response. To study melanoma heterogeneity, we generated twenty-four clonal sublines, each derived from a single cell isolated from a parental cell line derived from the M4 mouse melanoma model. DNA prepared from each subline and a spleen from a healthy mouse were subjected to long-read sequencing. Importantly, long-read sequencing allows direct detection of methylation states, small variants, and structural variants in the same run. The results thus provide excellent means to study genetic and epigenetic factors in clonal evolution. Each of these sublines was also implanted in distinct mice for survival and tumor growth analysis and further functional evaluation. We developed Severus, a structural variation (SV) caller for long reads, which works with single (germline), paired (tumor-normal), and multiple samples (e.g., multi-site or time series). Severus takes advantage of improved phasing in long-read sequencing, attributes somatic variants to germline haplotype, and builds a haplotype-specific breakpoint graph that is used to cluster multi-break rearrangements and represent the derived chromosomal structure. We benchmarked Severus using multiplatform validated COLO829 truthset and CHM1/CHM13 haploid genomes, and Severus outperformed all other methods in terms of recall and precision. The structural variation (SV) analysis using Severus with all the sublines showed enrichment of possibly clonal SVs in chr4, chr11, and mainly in chr13. Further investigation revealed SVs in chr13 were not distributed across the chromosome but clustered in certain regions. Analysis of somatic SNVs in chr13 corroborates the localized hypermutation profile, which indicates a possible kataegis. Interestingly, a loss of the chr13 copy affected by kataegis in one of the sublines coincides with a better survival rate, as compared to other sublines, in an allograft melanoma mouse model, which further supports the association between the kataegis and tumor progression. We also identified other clonal and subclonal events, including the homozygous deletion of Cdkn2a in most of the sublines, associated with their aggressiveness in vivo. Our analysis allowed us to identify clonal and subclonal genetic and epigenetic factors involved in tumor progression and evolution in a melanoma model, which can potentially translate to human disease. Citation Format: Ayse Keskus, Anton Goretsky, Yuelin Liu, Xiwen Cui, Tanveer Ahmad, Eva Perez Guijarro, Asher Bryant, Erin Malloy, Salem Malikic, Glenn Merlino, Chi-Ping Day, Cenk Sahinalp, Mikhail Kolmogorov. Melanoma clonal subline analysis reveals genetic factors driving intra-tumor heterogeneity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7407.

A novel grading system combining histological grade and CDKN2A homozygous and hemizygous deletion to predict prognosis in IDH-mutant astrocytoma.

Isocitrate dehydrogenase (IDH)-mutant astrocytoma with microvascular proliferation, necrosis, CDKN2A/B homozygous deletion, or any combination of these features corresponds to World Health Organization grade 4 according to current criteria. However, the prognostic significance of CDKN2A hemizygous deletion in IDH-mutant astrocytoma is not well established. We undertook a comprehensive study that included assessments of histological and genetic approaches to prognosis for these tumors. Samples from a cohort of 114 patients with extended observation were subjected to histological review and molecular analysis. CDKN2A (9p21) deletion was detected by fluorescence in situ hybridization. Overall survival (OS) was calculated via Kaplan-Meier estimation using the log-rank test. Histological grade, Ki-67 index, and the extent of surgical resection correlated with the OS of IDH-mutant astrocytoma patients. Both CDKN2A homozygous deletion and hemizygous deletion were detectable. Patients with CDKN2A homozygous-deletion tumors had the poorest OS; those with CDKN2A hemizygous-deletion tumors had an intermediate OS (p < .001). We then established a novel grading system that combined CDKN2A homozygous and hemizygous deletions with histological grade; the combined grading system was an independent prognostic factor for IDH-mutant astrocytomas. We conclude that CDKN2A homozygous and hemizygous deletion should be combined in a grading system for IDH-mutant astrocytomas.

Improved prognostic stratification of patients with isocitrate dehydrogenase-mutant astrocytoma

Prognostic factors and standards of care for astrocytoma, isocitrate dehydrogenase (IDH)-mutant, CNS WHO grade 4, remain poorly defined. Here we sought to explore disease characteristics, prognostic markers, and outcome in patients with this newly defined tumor type. We determined molecular biomarkers and assembled clinical and outcome data in patients with IDH-mutant astrocytomas confirmed by central pathology review. Patients were identified in the German Glioma Network cohort study; additional cohorts of patients with CNS WHO grade 4 tumors were identified retrospectively at two sites. In total, 258 patients with IDH-mutant astrocytomas (114 CNS WHO grade 2, 73 CNS WHO grade 3, 71 CNS WHO grade 4) were studied. The median age at diagnosis was similar for all grades. Karnofsky performance status at diagnosis inversely correlated with CNS WHO grade (p < 0.001). Despite more intensive treatment upfront with higher grade, CNS WHO grade was strongly prognostic: median overall survival was not reached for grade 2 (median follow-up 10.4 years), 8.1 years (95% CI 5.4–10.8) for grade 3, and 4.7 years (95% CI 3.4–6.0) for grade 4. Among patients with CNS WHO grade 4 astrocytoma, median overall survival was 5.5 years (95% CI 4.3–6.7) without (n = 58) versus 1.8 years (95% CI 0–4.1) with (n = 12) homozygous CDKN2A deletion. Lower levels of global DNA methylation as detected by LINE-1 methylation analysis were strongly associated with CNS WHO grade 4 (p < 0.001) and poor outcome. MGMT promoter methylation status was not prognostic for overall survival. Histomolecular stratification based on CNS WHO grade, LINE-1 methylation level, and CDKN2A status revealed four subgroups of patients with significantly different outcomes. In conclusion, CNS WHO grade, global DNA methylation status, and CDKN2A homozygous deletion are prognostic in patients with IDH-mutant astrocytoma. Combination of these parameters allows for improved prediction of outcome. These data aid in designing upcoming trials using IDH inhibitors.

Analysis of Histomorphologic/Molecular Association and Immune Checkpoint Regulators in Epithelioid Glioblastoma and Pleomorphic Xanthoastrocytoma: Are These Tumors Potential Candidates for Immune Checkpoint Blockade?

Accurate diagnosis of Epithelioid glioblastoma (eGB) and pleomorphic xanthoastrocytoma (PXA) is sometimes challenging owing to overlapping histologic and genetic features. There are limited reports on the immune profile of these tumors. In this study, we assessed 21 PXA [15 PXA Grade 2 (PXAG2); 6 PXA Grade 3 (PXAG3)] and 14 eGB for their histopathological and molecular association. Further, their immune profile was compared with GB, IDH1 wild-type (wt) (n-18). Morphologically, PXAG2 mostly differed from eGB; however, it was occasionally difficult to differentiate PXAG3 from eGB due to their epithelioid pattern and less obvious degenerative features. PXAG2 showed predominantly diffuse, whereas variable positivity for epithelial and glial markers was seen in PXAG3 and eGB. All cases showed retained nuclear ATRX and INI-1 . H3K27M or IDH1 mutation was seen in none. P53 mutation was more common in eGB, followed by PXAG3, and least common in PXAG2. BRAF V600E mutation was observed in 66.67% PXAG2, 33.33% PXAG3, and 50% eGB, with 100% concordance between immunohistochemistry (IHC) and sequencing. Thirty-six percent eGB, 33% PXAG3, and 61% PXAG2 harbored CDKN2A homozygous deletion. EGFR amplification was observed in 14% eGB and 66% of GB, IDH wt. PDL1 and CTLA-4 expression was higher in eGB (71.4% and 57.1%), PXAG3 (66.6% and100%), and PXAG2 (60% & 66.7%) as compared with GB, IDH wt (38.8% and 16.7%). Tumor-infiltrating lymphocytes were also observed in a majority of eGB and PXA (90% to 100%) in contrast to GB, IDH wt (66%). This analysis highlights the homogenous molecular and immune profile of eGB and PXA, suggesting the possibility that histologically and molecularly, these two entities represent 2 ends of a continuous spectrum with PXAG3 lying in between. Higher upregulation of PDL1, CTLA-4, and increased tumor infiltrating lymphocytes in these tumors as compared with GB, IDH wt suggests potential candidature for immunotherapy.

Reliability assessment of methylthioadenosine phosphorylase immunohistochemistry as a surrogate biomarker for CDKN2A homozygous deletion in adult-type IDH-mutant diffuse gliomas.

According to the 2021 World Health Organization classification of brain tumors, astrocytomas containing a CDKN2A/B homozygous deletion (HD) are designated as grade 4 even when no microvascular proliferation and/or necrosis is present. In this study, we aimed to investigate the relationship between CDKN2A HD and loss of methylthioadenosine phosphorylase (MTAP) expression in adult-type IDH-mutant gliomas and to assess the sensitivity and specificity of MTAP immunohistochemistry (IHC) along with interobserver agreement as a surrogate biomarker for CDKN2A HD. Eighty-eight astrocytomas and 71 oligodendrogliomas cases that were diagnosed between 2014 and 2021 at Hacettepe University were selected and tissue microarrays were conducted to perform CDKN2A fluorescence in situ hybridization and MTAP IHC. Twenty-five (15.7%) cases harbored CDKN2A HD. MTAP loss was detected in 28 (15.7%) cases by the first observer and 27 (17%) cases by the second observer. The sensitivity and specificity of MTAP were calculated as 88% and 95.52%-96.27% for 2 observers. A very good/perfect agreement was noted between the observers (Cohen kappa coefficient = 0.938). Intratumoral heterogeneity was observed in 4 cases. MTAP IHC was found to be a reliable surrogate biomarker as a possible alternative to CDKN2A HD identification with a high sensitivity and specificity along with high interobserver agreement.

FISH analysis reveals CDKN2A and IFNA14 co-deletion is heterogeneous and is a prominent feature of glioblastoma.

Deletion of CDKN2A occurs in 50% of glioblastomas (GBM), and IFNA locus deletion in 25%. These genes reside closely on chromosome 9. We investigated whether CDKN2A and IFNA were co-deleted within the same heterogeneous tumour and their prognostic implications. We assessed CDKN2A and IFNA14 deletions in 45 glioma samples using an in-house three-colour FISH probe. We examined the correlation between p16INK4a protein expression (via IHC) and CDKN2A deletion along with the impact of these genomic events on patient survival. FISH analyses demonstrated that grades II and III had either wildtype (wt) or amplified CDKN2A/IFNA14, whilst 44% of GBMs harboured homozygous deletions of both genes. Cores with CDKN2A homozygous deletion (n = 11) were negative for p16INK4a. Twenty p16INK4a positive samples lacked CDKN2A deletion with some of cells showing negative p16INK4a. There was heterogeneity in IFNA14/CDKN2A ploidy within each GBM. Survival analyses of primary GBMs suggested a positive association between increased p16INK4a and longer survival; this persisted when considering CDKN2A/IFNA14 status. Furthermore, wt (intact) CDKN2A/IFNA14 were found to be associated with longer survival in recurrent GBMs. Our data suggest that co-deletion of CDKN2A/IFNA14 in GBM negatively correlates with survival and CDKN2A-wt status correlated with longer survival, and with second surgery, itself a marker for improved patient outcomes.

“De novo replication repair deficient glioblastoma, IDH-wildtype” is a distinct glioblastoma subtype in adults that may benefit from immune checkpoint blockade

Glioblastoma is a clinically and molecularly heterogeneous disease, and new predictive biomarkers are needed to identify those patients most likely to respond to specific treatments. Through prospective genomic profiling of 459 consecutive primary treatment-naïve IDH-wildtype glioblastomas in adults, we identified a unique subgroup (2%, 9/459) defined by somatic hypermutation and DNA replication repair deficiency due to biallelic inactivation of a canonical mismatch repair gene. The deleterious mutations in mismatch repair genes were often present in the germline in the heterozygous state with somatic inactivation of the remaining allele, consistent with glioblastomas arising due to underlying Lynch syndrome. A subset of tumors had accompanying proofreading domain mutations in the DNA polymerase POLE and resultant “ultrahypermutation”. The median age at diagnosis was 50 years (range 27–78), compared with 63 years for the other 450 patients with conventional glioblastoma (p < 0.01). All tumors had histologic features of the giant cell variant of glioblastoma. They lacked EGFR amplification, lacked combined trisomy of chromosome 7 plus monosomy of chromosome 10, and only rarely had TERT promoter mutation or CDKN2A homozygous deletion, which are hallmarks of conventional IDH-wildtype glioblastoma. Instead, they harbored frequent inactivating mutations in TP53, NF1, PTEN, ATRX, and SETD2 and recurrent activating mutations in PDGFRA. DNA methylation profiling revealed they did not align with known reference adult glioblastoma methylation classes, but instead had unique globally hypomethylated epigenomes and mostly classified as “Diffuse pediatric-type high grade glioma, RTK1 subtype, subclass A”. Five patients were treated with immune checkpoint blockade, four of whom survived greater than 3 years. The median overall survival was 36.8 months, compared to 15.5 months for the other 450 patients (p < 0.001). We conclude that “De novo replication repair deficient glioblastoma, IDH-wildtype” represents a biologically distinct subtype in the adult population that may benefit from prospective identification and treatment with immune checkpoint blockade.

10233-GMC-17 CLINICAL SIGNIFICANCE OF GENETIC ANALYSIS FOR GLIOMA CASES IN OUR INSTITUTE

Abstract The WHO Classification the 5th edition describes that identification of alterations in IDH gene, histone H3 gene, CDKN2A gene, and other genes are quite important for the diagnosis and grading of diffuse gliomas. It is important to efficiently analyze important genetic abnormalities and utilize them in actual clinical practice. In our institute, we have recently performed genetic analysis which is important for the diagnosis of glioma in all patients. Here, we report the results of these analyses. From March 2019 to June 2023, we performed Sanger sequencing for analyses of IDH1/2, H3F3A, TERT promoter, BRAF, and FGFR1 mutation in 235 patients with suspected glioma who underwent biopsy or resection at our hospital and affiliated institutions. In 145 cases, we performed MLPA analyses for detection of 1p/19q codeletion, CDKN2A homozygous deletion (HD), EGFR amplification, and Chromosome 7p gain/10q loss. Sanger sequencing identified 81 TERT promoter mutations, 70 IDH mutations (including 3 IDH2 mutations), 8 BRAF V600E mutations, 4 H3 K27M mutations, 3 H3 G34R/V mutations, and 1 FGFR1 mutation The alterations most frequently identified in MLPA were CDKN2A HD in 26 cases and 1p/19q codeletion in 19 cases. Of the 214 cases in which the pathology diagnosis was neoplastic disease, 85 (39.8%) had no abnormalities in the above genetic analysis. In 32 of these cases, the pathological diagnosis was glioblastoma, IDH-wildtype, while in many other cases, the pathological diagnosis was low-grade glioma. Genetic analysis focusing on important genes for diagnosis according to WHO classification the 5th edition was useful for diagnosis in many cases, but careful consideration is needed for diagnosis in cases without these genetic alterations.

Abstract C135: Discovery of novel MTA-cooperative PRMT5 inhibitors as targeted therapeutics for MTAP-deleted cancers

Abstract Homozygous deletions of the p16/CDKN2a (cyclin dependent kinase inhibitor 2A) locus, which is responsible for regulating the cell cycle, are commonly found in cancer and often involve the deletion of adjacent genes. One such adjacent gene is methylthioadenosine phosphorylase (MTAP), involved in metabolism, located on chromosome 9p21 in close proximity to the p16/CDKN2A tumor-suppressor locus. Co-deletion of MTAP is observed in approximately 80-90% of tumors with homozygous deletion of CDKN2A, representing 10-15% of all human tumors. These tumor types, including non-small cell lung cancer, pancreatic adenocarcinoma, glioblastoma, and mesothelioma, have a poor prognosis, highlighting the significant unmet medical need in this area. Deletion of MTAP leads to a significant accumulation of methylthioadenosine (MTA) in cells. MTA, at high concentrations, selectively inhibits the PRMT5 methyltransferase enzyme, competing with the substrate S-adenosylmethionine (SAM) required for methylation reactions. As a result, the overall level of symmetric arginine dimethylation throughout the proteome is reduced. This heightened sensitivity to modulation of methylosome activity makes cells with MTAP deletion more susceptible to therapeutic targeting of PRMT5. Hence, selective targeting of PRMT5 in cancers with homozygous MTAP deletion represents a promising strategy for specifically eliminating cancer cells with this genetic alteration. Ryvu is developing two independent series of PRMT5 inhibitors characterized by good drug-like physicochemical properties and inhibition of methyltransferase activity with IC50 values in the low nanomolar range. Structure-based lead optimization enabled rapid expansion and delivery of a compound library with novel intellectual property (IP), high target engagement in cells and selective potency in MTAP-deleted cell lines. In long-term three-dimensional (3D) cell culture, Ryvu compounds selectively inhibit the growth of MTAP-deficient cancer cells, which correlate strongly with the inhibition of PRMT5-dependent symmetric protein dimethylation (SDMA) in these cells. The synthesized library allowed the identification of compounds with more than 350-fold selectivity between the effects observed in MTAP-deficient and WT cells for both SDMA and growth inhibition. The DMPK profile of these compounds allows for oral administration, which enables testing of antitumor activity in MTAP null tumor xenograft bearing mice. The correlation between compound exposure and on-target effect was confirmed in PK/PD and efficacy studies. Taken together, these studies provide a rationale for the further development of our chemical series of MTA cooperative PRMT5 inhibitors toward a clinical candidate. Citation Format: Adam Radzimierski, Aneta Bobowska, Agata Stachowicz, Kamil Kus, Kamila Kozłowska-Tomczyk, Agnieszka Ludwig-Słomczyńska, Aniela Gołas, Paulina Podkalicka, Andrzej Gondela, Nicolas Boutard, Grzegorz Ćwiertnia, Krzysztof Brzózka, Anna Bartosik, Mateusz Nowak, Didier Pez. Discovery of novel MTA-cooperative PRMT5 inhibitors as targeted therapeutics for MTAP-deleted cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C135.

PATH-40. “DE NOVO REPLICATION REPAIR DEFICIENT GLIOBLASTOMA, IDH-WILDTYPE” IS A DISTINCT GLIOBLASTOMA SUBTYPE IN ADULTS THAT MAY BENEFIT FROM IMMUNE CHECKPOINT BLOCKADE

Abstract Glioblastoma is clinically and molecularly heterogeneous, and new predictive biomarkers are needed to identify those patients most likely to respond to specific treatments. Through prospective genomic profiling of 459 primary treatment-naïve IDH-wildtype glioblastomas in adults, we identified a subgroup (2%, 8/459) defined by somatic hypermutation and DNA replication repair deficiency due to mismatch repair gene inactivation and/or proofreading domain mutation in the DNA polymerase POLE. The deleterious mutations in mismatch repair genes were often present in the germline in the heterozygous state with somatic inactivation of the remaining wildtype allele, consistent Lynch syndrome-associated glioblastomas. All tumors were hypermutated ( &amp;gt;20 somatic nonsynonymous mutations/Mb), while the three tumors with POLE mutations were “ultrahypermutated” with &amp;gt;150 mutations/Mb. The median age at diagnosis was 52 years (range 27-78), compared with median age of 63 years for the other 451 patients with conventional glioblastoma. All tumors were diffuse astrocytic gliomas of the giant cell histologic subtype. They lacked EGFR amplification and only rarely had TERT promoter mutation (1/8), CDKN2A homozygous deletion (1/8), or the combination of trisomy 7 and monosomy 10 (1/8). Instead, they harbored frequent inactivating mutations in the TP53, NF1, PTEN, ATRX, and SETD2 genes ( &amp;gt;50% each) and recurrent activating mutations in PDGFRA (4/8). DNA methylation profiling revealed they did not align with known glioblastoma methylation classes, but instead mostly classified as “Diffuse pediatric-type high grade glioma, RTK1 subtype, subclass A (novel)”. Some patients were treated with immune checkpoint blockade (nivolumab or pembrolizumab) and survived over three years. The median overall survival for the cohort was 37.4 months (95% CI: 22-not reached), compared to 15.4 months (95% CI: 14.7-17.9) for the other 451 patients. We speculate that “de novo replication repair deficient glioblastoma, IDH-wildtype” represents a biologically distinct subtype that may benefit from prospective identification and treatment with immune checkpoint blockade.

TMET-06. METABOLOGENOMIC CHARACTERIZATION UNCOVERS HETEROGENEITY AMONGST IDH MUTANT

Abstract INTRODUCTION Mutations in isocitrate dehydrogenase (IDH) enzymes are recognised to drive the molecular footprint of diffuse gliomas through the accumulation of oncometabolite R-2-hydroxyglutarate which drives the widespread restructuring of the DNA methylome; however, beyond R-2-hydroxyglutarate , a comprehensive metabologenomic characterization of IDH-mutant gliomas has yet to be performed. We aimed to characterize the global metabolic profile of IDH-mut and IDH-wt gliomas, identify clinically relevant subgroups based on distinct metabolic differences, and utilize matched epigenetic and transcriptional data to characterize these distinct groups. Method: Glioma samples from a cohort of 154 patients underwent multiplatform molecular analysis, including metabolomic studies, genome-wide DNA methylation profiling and bulk RNA sequencing. A integrative analysis was performed, including hierarchical clustering and principal component analysis of identified metabolites, differentially methylated probes, copy number alteration and bulk mRNA data. Survival analysis as well as multivariable hazard ratios for clinical variables were calculated by fitting Cox Proportional Hazards Models. RESULTS We discovered a group of IDH-mutant gliomas whose metabolic profile highly resembled IDH wildtype tumors. Notably, these IDH-mutant gliomas with dysregulated metabolism were distinguished from their IDH-mutant counterparts by significantly shorter overall survival (median OS 118.9 months vs 173.6 months, p=0.048). The IDH-mutant tumors with dysregulated metabolism harbored distinct epigenetic alterations that converged to drive proliferative and stem-like transcriptional profiles. The prognostic relevance of dysregulated metabolism complements, but was not wholly explained by canonically recognized prognostic classifications in IDH-mutant gliomas including 1p/19q codeletion, glioma CpG Island Hypermethylator (GCIMP) status and CDKN2A homozygous deletion. CONCLUSION Utilizing a cross-platform analysis we have uncovered a novel subtyping of IDH-mutant gliomas with dysregulated cellular metabolism with similar survival to IDH-wildtype tumors. The metabolic profile provides unique information on glioma phenotypes, which may facilitate a more comprehensive understanding of glioma biology, and provide a window to target novel dependencies.

PATH-50. GENETIC AND EPIGENETIC PROFILING OF MENINGIOMAS TO GAIN INSIGHTS INTO MOLECULAR HETEROGENEITY AND RISK STRATIFICATION.

Abstract BACKGROUND Meningiomas are slow-growing CNS tumors, with most being benign (WHO grade 1) and having indolent behavior. Limited data on molecular profiling of meningiomas and its clinical implications have hindered the implementation of effective therapies and new treatments. Aims &amp; Objectives: Perform DNA methylation profiling, copy number analysis, and targeted sequencing in meningiomas. MATERIALS &amp; METHODS 208 meningiomas, grade 1 (n=109), grade 2 (n=83), and grade 3 (n=16)were assessed for pTERT mutation, CDKN2A homozygous deletion, and H3K27me3 expression. Additionally, 35 diagnostically challenging meningiomas underwent DNA methylation profiling, copy number analysis, and targeted sequencing. RESULTS there were 199 adult and 9 pediatric cases, (mean age 44.5 years). The tumors were located in basal (53%) ,convexity (42%),and 5% in other locations.pTERT C228T mutation was detected in 4.8% and CDKN2A deletion in 2.4% cases. Loss of H3K27me3 expression was found in a significant proportion of tumors across all three grades. Methylation profiling identified four distinct molecular subgroups: Malignant, Intermediate, Benign A, and Benign B. Intermediate, Benign A, and Benign B subgroups included both WHO grade 1 and grade 2 cases. Mutations showed a strong association with specific methylation subgroups (NF2, AKT1, SMO, TRAF7, and pTERT). Loss of chromosome 22q was observed in all subgroups. 1p/14q co-deletion was predominantly seen in the malignant and intermediate subgroups (50%). CDKN2A loss was mainly observed in the malignant subgroup (50%). The DKFZ classifier successfully classified 71% of cases with an acceptable score. Methylation profiling significantly influenced PFS in WHO grade 1 and 2 meningiomas (p=0.0051). CONCLUSIONS Genome-wide DNA methylation profiling reveals clinically distinct molecular subgroups and heterogeneity within the same grade of meningiomas and is particularly valuable for identifying high-risk cases and predicting prognosis in WHO grade 1 and 2 meningiomas. The pTERT mutation serves as a significant and cost-effective marker for risk stratification in meningiomas.

PATH-19. PROGNOSTIC FACTORS, RESPONSE TO TREATMENT, AND OUTCOME OF PATIENTS WITH ISOCITRATE DEHYDROGENASE (IDH)-MUTANT ASTROCYTOMA, CNS WHO GRADE 4

Abstract PURPOSE To study disease characteristics, prognostic markers and outcome in patients with isocitrate dehydrogenase (IDH)-mutant astrocytoma by CNS WHO grade. EXPERIMENTAL DESIGN We determined molecular biomarkers and assembled clinical and outcome data in a cohort of 258 patients with IDH-mutant astrocytomas (114 CNS WHO grade 2, 73 CNS WHO grade 3, 71 CNS WHO grade 4) confirmed by central pathology review. RESULTS The median age for astrocytoma, IDH mutant, CNS WHO grade 4, was 37 (range: 23-79 years) and similar to patients with CNS WHO grade 2 or 3 tumors. Karnofsky performance status at diagnosis inversely correlated with CNS WHO grade (p&amp;lt; 0.001). Despite more intensive treatment upfront with higher grade, CNS WHO grade was strongly prognostic: median overall survival was 22.2 years (95% n.a.) for grade 2, 8.1 years (95% 5.4-10.8) for grade 3 and 4.7 years (95% 3.4-6.0) for grade 4. Among patients with CNS WHO grade 4 astrocytoma, median overall survival was 5.5 years (95% 4.3-6.7) without (n=58) versus 1.8 years (95% 0-4.1) with (n=12) homozygous CDKN2A homozygous deletion. Reduced global DNA methylation as indicated by LINE-1 methylation levels was strongly associated with CNS WHO grade 4 (p&amp;lt; 0.001) and poor outcome among IDH-mutant astrocytoma patients. MGMT promoter methylation status was not prognostic for overall survival. CONCLUSIONS The CNS WHO grade is prognostic in patients with IDH-mutant astrocytoma. CDKN2A homozygous deletion and reduced LINE-1 methylation levels are linked to CNS WHO grade 4 and associate with shorter survival. These data serve to inform on clinical trial designs, e.g., using IDH inhibitors, in this patient population.

PATH-44. INTRA-OPERATIVE ANALYSES OF GENETIC ALTERATIONS IN THE CENTRAL NERVOUS SYSTEM TUMORS USING RAPID QUANTITATIVE PCR DEVICE

Abstract Recent comprehensive molecular analyses of central nervous system (CNS) tumors identified several diagnostic or prognostic markers. IDH mutation, TERT promoter (pTERT) mutation and CDKN2A homozygous deletion in adult-type diffuse gliomas, BRAF p.V600E mutation in circumscribed astrocytic gliomas, histone H3 gene mutations in pediatric-type diffuse high-grade gliomas or MYD88 mutation in primary CNS lymphoma (PCNSL) are quite important markers. Intra-operative identification of these molecular alterations could be effective for decision-making of tumor removal strategy. In this study, we established intra-operative gene analysis method using rapid quantitative PCR device, GeneSoC, by which we could obtain genotype of these important genes for 20 minutes in an operating room. Using GeneSoC, we could perform 50 cycles of quantitative PCR for approximately 12 minutes. We established rapid gene analyses of mutations of IDH1 p.R132H, pTERT C225T, pTERT C250T, H3 K27M, BRAF p.V600E and homozygous deletion of CDKN2A for diffuse gliomas and circumscribed astrocytic tumors and MYD88 p.L265P for PCNSL. For elution of DNA, we incubated at least 1mg of tumor tissue at 95°for 5 minutes. Combined this boiling method with GeneSoC, we could obtain those genetic alterations for 20 minutes after collection of tumor tissue. For 42 glioma cases and 10 PCNSL cases, we could obtain accurate genetic alterations (IDH1 p.R132H, pTERT C225T, pTERT C250T for gliomas or MYD88 p.L265P for PCNSL) in all cases, using this method. For detection of CDKN2A homozygous deletion, sensitivity and specificity are 100% and 83% in analyzed 50 cases, respectively. In this study, we could obtain the genotype of important molecular markers intra-operatively, not only during tumor removal but even during tumor biopsy, using GeneSoC device. This rapid genetic analysis might be effective not only for intra-operative diagnosis but also for detection of boundary between tumor and normal tissue.