Differential impact of IDH1/2 mutational subclasses on outcome in adult AML: Results from a large multicenter study

Mutations of the isocitrate dehydrogenase-1 (IDH1) and IDH2 genes are amongst the most frequent alterations in acute myeloid leukemia (AML) and can be found in ~20% of patients at diagnosis. Among 4930 patients (median age 56 years, interquartile range 45-66) with newly diagnosed, intensively treated AML, we have identified IDH1 mutations (mIDH1) in 423 (8.6%) and IDH2 mutations (mIDH2) in 575 (11.7%) patients. Overall, there were no differences in response rates or survival for patients with mIDH1 or mIDH2 compared to patients without mutated IDH1/2. However, distinct clinical and co-mutational phenotypes of the most common subtypes of IDH1/2 mutations could be associated with differences in outcome. IDH1-R132C was associated with significantly increased age, lower white blood cell count (WBC), less frequent co-mutation of NPM1 and FLT3-ITD as well as lower rate of complete remissions and a trend for reduced overall survival (OS) compared to other mIDH1 variants and wtIDH1/2. In our analysis, IDH2-R172K was associated with significantly lower WBC, more karyotype abnormalities, and less frequent co-mutations of NPM1 and/or FLT3-ITD. Among patients within the ELN2017 intermediate- and adverse-risk groups, RFS and OS were significantly better for patients with IDH2-R172K compared to wtIDH, providing evidence that AML with IDH2-R172K could be a distinct entity with a specific co-mutation pattern and favorable outcome. In summary, the presented data from a large cohort of IDH1/2 mutant AML patients indicate novel and clinically relevant findings for the most common IDH-mutation subtypes.

Differential Prognostic Impact of IDH1 and IDH2 Mutations in Chronic Myelomonocytic Leukemia

Introduction: Mutations involving isocitrate dehydrogenase 1/2 (IDH) are known oncogenic drivers in hematological malignancies, conferring neomorphic enzymatic activity to IDH 1/2, resulting in the oncometabolite, 2-hydroxyglutarae (2-HG). 2-HG in turn suppresses TET activity, making IDH and TET2 mutations synthetically lethal and almost mutually exclusive. The frequency of IDH mutations in CMML is <10% and their prognostic impact remains unclear. We carried out this study in a large database of molecularly annotated CMML patients to better define the clinical profile and prognostic impact of these mutations. Methods: After IRB approval, CMML patients from the Mayo Clinic, Minnesota and the Moffitt Cancer Center (MCC), Tampa, Florida, were included in the study. All patients had bone marrow (BM) biopsies with cytogenetics and molecular genetics done either at diagnosis, or at first referral. Clinical and mutational data were abstracted and retrospectively analyzed. Overall survival (OS) was calculated from date of CMML diagnosis to date of death/last follow, while AML-free survival (AML-FS) was calculated from date of CMML diagnosis to date of leukemic transformation (LT). Patients that had undergone allogeneic HCT were excluded from the study (n=3). Statistical analysis was carried out using the Blue Sky software. Results: Six hundred and forty four patients were included in the study (Mayo Clinic-357, MCC- 287), median age 71 years (range, 20-95 years), 67.8% being male. Forty-three (6.7%) patients had IDH mutations, 35 (82%) IDH2 and 8 (18%) IDH1; of which, 34 (97%) involved the IDH2R140 hotspot and 5 (62.5%) involved the IDH1R132 hotspot, respectively. The median variant allele fractions (VAF) for IDH1 mutations was 41% (range, 8-46%) and for IDH2 mutations was 46% (range, 7-70%). There were no significant demographic or clinical differences between IDH mutant and wild type CMML patients, with the exception that IDH mutant CMML patients were less likely to be thrombocytopenic (p=0.006), were less likely to have TET2 co-mutations (14% vs 53.2%; p<0.001) and were more likely to have SRSF2 co-mutations (69.8% VS 40.3%; p<0.001). Importantly there were no differences in proliferative or dysplastic subtypes (p=0.3), cytogenetic (p=0.12) and molecular risk stratifications (p=045). There were also no significant demographic or clinical differences between IDH1 vs IDH2 mutant CMML patients. Six (14%) IDH mutant CMML patients had TET2 co-mutations; 5 (83%) with IDH2R140Q (median VAF-28%;all male) and 1 (17%) with IDH1R132H (VAF-44%;female) (Figure 1). Five (11%) IDH2 mutant patients were treated with enasidenib (IDH2 inhibitor), none with a durable response, while none of the IDH1 mutant patients received targeted therapy. At last follow up (median 18 months), 337 (52%) deaths and 119 (18.5%) LT have been documented, with IDH mutant patients having a higher LT rate (30.2% vs 17.6%, p=0.04) compared to wildtype patients. The median OS of the entire cohort was 35 months, with no difference in OS between IDH mutant and wild type patients (34.5 vs 35 months, p=0.12), with IDH1 mutant patients having a shorter OS in comparison to IDH2 mutant patients (31 vs 37 months; p=0.005- Figure 1). IDH mutant CMML patients also had a shorter AML-FS in comparison to wild type patients (36.6 vs 210 months, p=0.005), with there being no differential impact on AML-FS of IDH1 vs IDH2 mutations (p=0.26, Figure 1). Conclusions: IDH mutations are infrequent in CMML (7%), with IDH2 mutations being more common than IDH1 mutations (80 vs 20%). IDH mutations co-occur very infrequently with TET2 mutations (14%), with IDH mutant patients being less likely to have thrombocytopenia and more likely to have SRSF2 co-mutations. IDH mutations negatively impacting AML-FS without a significant impact on OS. Prospective clinical trials testing the safety and efficacy of IDH1/2 inhibitors in CMML are much needed. Figure 1 Figure 1. Disclosures Komrokji: AbbVie: Consultancy; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees; Taiho Oncology: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Speakers Bureau; Acceleron: Consultancy; BMSCelgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Geron: Consultancy. Al-Kali: Novartis: Research Funding; Astex: Other: Research support to institution. Padron: BMS: Research Funding; Stemline: Honoraria; Taiho: Honoraria; Kura: Research Funding; Incyte: Research Funding; Blueprint: Honoraria. Patnaik: StemLine: Research Funding; Kura Oncology: Research Funding.

Clonal Dynamics of IDH1 Mutations in Acute Myeloid Leukemia

Introduction: Isocitrate dehydrogenase 1 (IDH1) gene is mutated in 7-14% of acute myeloid leukemia (AML) patients. IDH1 encodes for an enzyme that catalyzes the conversion of isocitrate to α- ketoglutarate. IDH1 mutation leads to accumulation of the oncometabolite 2-hydroxyglutarate. Clonal evolutionary dynamics of IDH1 mutations in AML have not been clearly characterized. The introduction of targeted small-molecule therapy, Ivosidenib, in AML treatment underscores the significance of understanding the topography of clonal dynamics in IDH1-mutated AML to optimize precision medicine. Methods: We analyzed ~6000 patients with next-generation sequencing (NGS) data and identified 107 patients with IDH1 mutated AML. Disease status was determined for each NGS test date by manual chart review. IDH1 mutation status was characterized during course of AML at diagnosis, remission, relapse, and with persistent disease. Cytogenic risk category was determined using ELN 2017 guidelines. Kaplan Meier survival analysis and log-rank test were used to determine significant differences in overall survival among patient groups. Results: Of the 107 total patients, 39 patients (36%) had AML with myelodysplastic-related changes (AML-MRC) and 39 patients (36%) had AML-NOS. The most frequently co-mutated genes were SRSF2, DNMT3A, ASXL1, RUNX1, NRAS, BCOR, STAG2, NPM1, JAK2, and FLT-3 in order of frequency. Of the total patients, 74 patients (69%) had good cytogenetics, 17 patients (16%) had intermediate cytogenetics, and 16 patients (15%) had poor/very poor cytogenetics. Among the patients with IDH1-mutated AML, 85 patients (79%) were IDH1-positive at initial diagnosis, while 22 patients (21%) were IDH1- negative at diagnosis and acquired the mutation later in disease course. Of those 22 patients, 18 patients gained the mutation in the setting of persistent disease, 3 patients at remission, and 1 patient at relapse. In those with persistent AML (n=42), 30 patients (71%) remained IDH1-positive while 12 patients (29%) lost the mutation. In those achieving remission (n=66), 12 patients (18%) who were IDH1-positive remained IDH1-positive while 51 patients (77%) cleared the mutation. In those with relapsed disease (n= 21), 17 patients (81%) with IDH1-positive AML remained IDH1-positive while 4 patients (19%) lost the mutation at relapse. There were no significant differences in median overall survival in patients who were positive or negative for IDH1 mutations at diagnosis, positive or negative with disease persistence, or among patients who remained IDH1-positive or lost the IDH1 mutation at disease relapse. Patients that were IDH1-positive at diagnosis were more likely to have poorer cytogenetics than patients who were IDH1-negative at diagnosis (p=0.0016). Conclusion: In summary, this study found that IDH1 mutations are unstable throughout the course of AML and periodic genetic testing of AML patients is necessary for optimizing precision medicine approaches. In disease remission, most patients (77%) cleared the IDH1 mutation. In the relapse setting, 81% of patients retained IDH1-positive status. Our study, the largest of its kind to our knowledge, shows that serial genomic profiling for the IDH1 mutation across disease course may be beneficial in helping to tailor targeted therapy for IDH1+ AML. Disclosures Sweet: Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Sallman: Kite: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Aprea: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Intellia: Membership on an entity's Board of Directors or advisory committees; Magenta: Consultancy; Incyte: Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Shattuck Labs: Membership on an entity's Board of Directors or advisory committees; Syndax: Membership on an entity's Board of Directors or advisory committees. Hussaini: Adaptive: Consultancy, Honoraria, Speakers Bureau; Stemline: Consultancy; Amgen: Consultancy; Seattle Genetics: Consultancy; Celegene: Consultancy; Decibio: Consultancy; Guidepoint: Consultancy; Bluprint Medicine: Consultancy.

FDA Cleared Companion Diagnostics (CDx) Tests (IDH1, IDH2 and FLT3) for Acute Myeloid Leukemia (AML) Patient Care

Acute myeloid leukemia (AML) is one of the most lethal blood cancers from which nearly 10,000 people die in the United States each year. While therapies for other blood cancers have made some progress, the standard of care for AML, a combination of toxic chemotherapies, has changed very little over the past four decades. In recent years the US Food and Drug Administration (FDA) has been very active in approving targeted therapeutic drugs for AML patients including Midostaurin (Rydapt; 2017) and Gilteritinib (Xospata;2018) for FLT3 mutations; Enasidenib (Idhifa; 2017) for IDH2 mutations and Ivosidenib (Tibsovo; 2018) for IDH1 mutations. Additionally, the Leukemia and Lymphoma Society's Beat AML Master Clinical Trial has shown that waiting for molecular results prior to treatment decision leads to better outcomes. Versiti Blood Center of Wisconsin Diagnostics laboratory which is certified under the Clinical Laboratory Improvement Amendments (CLIA) and qualified to perform high complexity clinical laboratory testing has performed the verification studies and offers two companion diagnostics tests for IDH1 and IDH2 mutations for AML patients. Also, in collaboration with Invivoscribe Inc., the AML patient can be tested for Leukostrat CDx FLT3 mutations assay so that the same AML patient can get three CDx test results leading to available drug therapy treatment decision making by physicians. IDH1 CDX Test: IDH1 CDx is indicated as an aid in identifying AML patients with an IDH1 mutation for treatment with ivosidenib (TIBSOVO®). Mutations in codon R132 of IDH1 can be found in 6% to 10% of AML patients. The IDH1 CDx test detects five IDH1 mutations R132H (CAT), R132C (TGT), R132G (GGT), R132S (AGT), and R132L (CTT) using PCR technology with homogeneous real-time fluorescence detection. The assay sensitivity for these five IDH1 mutations is 100% at variant allele frequencies of 2% and higher and 98% or greater at variant allele frequencies of 1% and higher. This test has been approved by the FDA as companion diagnostic device (PMA number P170041). IDH2 CDx: IDH2 CDx is indicated as an aid in identifying AML patients with an IDH2 mutation for treatment with IDHIFA® (enasidenib). Mutations in the R140 and R172 codons of IDH2 8% to 19% of AML patients.The IDH2 CDX test detects nine IDH2 mutations (R140Q, R140L, R140G, R140W, R172K, R172M, R172G, R172S, and R172W) using PCR technology with real-time fluorescent detection. The assay sensitivity for these nine IDH2 mutations is 99.8% or greater at variant allele frequencies of 2% and higher or 93.5% or greater at variant allele frequencies of 1% and higher. This test has been approved by the FDA as companion diagnostic device (PMA number P170005). FLT3 CDx: The FLT3 Leukostrat® CDx Assay is the FDA approved (PMA number P160040) predictive test for the efficacy of midostaurin (RYDAPT®) therapy in all AML patients, regardless of cytogenetics and efficacy of gilteritinib (XOSPATA ® ) therapy in relapsed or refractory AML patients. FLT3 is one of the most commonly mutated genes in AML with 30% of patients at the time of diagnosis 1. The most prevalent type of FLT3 mutation is an internal tandem duplication (ITD) in the juxtamembrane domain. The second most common mutation type in the FLT3 gene is a tyrosine kinase domain (TKD) point mutation in the codon for an aspartate (D835) or an isoleucine (I836) residue. The LeukoStrat® CDx FLT3 Mutation Assay is a PCR-based, in vitro diagnostic test designed to detect internal tandem duplication (ITD) mutations and the tyrosine kinase domain (TKD) mutations D835 and I836 in genomic DNA extracted from mononuclear cells obtained from peripheral blood or bone marrow aspirates of patients diagnosed with AML. Versiti Blood Center sends the patient specimens to Invivoscribe Inc. where the LeukoStrat® CDx FLT3 Mutation Assay is performed and the interpretive comments are included in the patient report by Versiti. From our experience pathologists and treating physicians want molecular test results as fast as possible, especially for the actionable gene mutations in IDH1, IDH2 and FLT3. The IDH1 CDx, IDH2 CDx and FLT3 CDx tests are highly sensitive and Versiti provides average turn around time of 3 business days which enable rapid decision making on the recently available drug therapies for AML patients. We strongly recommend that the IDH1 CDx, IDH2 CDx and FLT3 CDx tests should be performed on all AML patients for better care. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: In recent years the US Food and Drug Administration (FDA) approved targeted therapeutic drugs for AML patients including Midostaurin (Rydapt; 2017) and Gilteritinib (Xospata;2018) for FLT3 mutations; Enasidenib (Idhifa; 2017) for IDH2 mutations and Ivosidenib (Tibsovo; 2018) for IDH1 mutations.

Ivosidenib Monotherapy Is Effective in Patients with IDH1 Mutated Myelodysplastic Syndrome (MDS): The Idiome Phase 2 Study By the GFM Group

Background: Ivosidenib (IVO) is an oral, targeted, small-molecule inhibitor of mutant IDH1 approved in the US for adult patients with unfit or relapse/refractory AML with IDH1 mutation. Little is known on its efficacy in patients with IDH1 mutated MDS. Here we report interim results of a Phase 2 study evaluating safety and efficacy of IVO in three different cohorts of MDS patients: Higher risk MDS having failed azacytidine (AZA) (cohort A, n=29), untreated higher risk MDS without life threatening cytopenias (ie ANC < 500/mm3 or any recent severe infections and/or platelets below 30,000/mm3 and any bleeding symptom,) as a first line treatment (cohort B, with the addition of AZA in non-Responders after 3 cycles, n=29) and lower risk MDS having failed EPO (cohort C, n=10). (ClinicalTrials.gov NCT03503409). Methods: Subjects enrolled in cohort A, B or C received continuous 28-day cycles of IVO - 500 mg orally QD. In cohort B, AZA (75 mg/m2/d x 7 days, SC) was added to IVO after 3 cycles, only in the absence of IWG 2006 response (absence of CR, PR or HI). The primary endpoint was overall hematological response rate (ORR) at 3 and 6 months (including CR, PR, stable disease with HI according to IWG 2006). All responders allowed to continue treatment until loss of response. Secondary endpoints included safety, duration of response, EFS, overall survival and translational project evaluating the role of biomarkers on response. We report the preliminary results on the first 26 pts enrolled. Results: At data cut off (6/15/2021), 32 patients had been enrolled, including 26 who were evaluable for the primary endpoint. 13, 11 and 2 were enrolled in cohort A, B and C respectively. Median age was 76 years and 50% were female. WHO was MDS-MLD, MDS-EB1, MDS-EB2, CMML and low blast count AML in 2, 2, 12, 1 and 9 patients respectively. IPSS-R was low, intermediate, high and very high in 2, 6, 5 and 13 resp. IDH1 mutation was p.R132C in 15 patients, p.R132H in 7, p.R132G/S in 3 and not specified in 1. The ORR was 69% (18 patients) including 12 CR (46%), 1 PR and 5 HI. Most patients achieved response after 3 cycles (17/18). Response was achieved in 7 (54%), 10 (91%) and 1 (50%) in cohort A, B and C respectively. Moreover, CR was achieved in 3, 8 and 1 in cohort A, B and C respectively. In cohort B, AZA was added to IVO in one patient after 3 cycles, without additional response. With a median follow up of 9.1 months, the median duration of response of the 18 responders was 7.4 months, 9 of them lost their response, and two had died without loss of response (from bleeding and after HSCT, respectively). IPSS-R was the only prognostic factor of response after 6 cycles. At data cut off, 12 patients had progressed (9 in cohort A, 2 in cohort B and 1 in cohort C) and 11 (42%, 10 in cohort A and 1 in cohort C) patients had died, mostly of relapse/progression (n=5/11), infection in 1, suicide in 1, hemorrhage in 1 and other unrelated causes in 3. Median overall survival was 14 months in the whole cohort, 7.7 and not reached in cohort A and B resp. The most common treatment-related serious adverse event (SAE) was differentiation syndrome (4/5), one died and three resolved without sequelae. One patient had febrile neutropenia related to IVO, resolved without sequelae. Conclusion: IVO was well tolerated in MDS patients with significant responses in all the cohorts. With a response rate of 91%, IVO was particularly effective in treatment naïve higher risk MDS patients with IDH1 mutations (cohort B). These encouraging preliminary results have to be confirm in more patients. The IDIOME study is still ongoing, and molecular monitoring results of IDH1 mutations will be presented. Disclosures Sebert: BMS: Consultancy; Abbvie: Consultancy. Cluzeau: Abbvie: Consultancy, Honoraria, Speakers Bureau; Roche: Consultancy, Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Speakers Bureau; Agios: Honoraria; Amgen: Speakers Bureau; Takeda: Other: travel, accommodations, expenses; Astellas: Speakers Bureau; Jazz Pharma: Consultancy, Honoraria; BMS/Celgene: Consultancy, Honoraria, Speakers Bureau; Pfizer: Other: travel, accommodations, expenses. Stamatoulas Bastard: Pfizer: Other: Travel Support; Celgene: Membership on an entity's Board of Directors or advisory committees. Fenaux: Abbvie: Honoraria, Research Funding; JAZZ: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Celgene/BMS: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Syros Pharmaceuticals: Honoraria. Ades: Abbvie: Honoraria; Takeda: Honoraria; Novartis: Honoraria; JAZZ: Honoraria; Celgene: Honoraria, Research Funding.

BIOM-17. DIFFERENCES IN THE IMMUNE MICROENVIRONMENT OF GLIOMAS HARBORING IDH2 VERSUS IDH1 MUTATIONS

INTRODUCTION IDH mutations are a defining feature of lower-grade glioma and secondary glioblastoma. Approximately 95% of glioma-associated IDH mutations are in codon 132 of IDH1, but a small proportion are in IDH2. IDH mutations produce the oncometabolite 2-hydroxyglutarate, which induces global DNA hypermethylation and is associated with an immunosuppressive tumor microenvironment. IDH1 is localized in the cytosol while IDH2 is found in the mitochondrial matrix, and mutations in these genes may have differing effects on the tumor microenvironment. METHODS Formalin-fixed, paraffin-embedded tissue from 633 IDH-mutant gliomas (615 IDH1-mutant, 18 IDH2-mutant) underwent whole-exome and whole-transcriptome sequencing at Caris Life Sciences (236 grade 2/3 astrocytoma, 158 grade 2/3 oligodendroglioma, 202 IDH-mutant glioblastoma, 37 glioma, NOS). QuantiSEQ was used to infer tumor-infiltrating immune cell populations from RNAseq data, and gene-set enrichment analyses (GSEA) were performed using Wikipathway. RESULTS IDH1-mutant gliomas had higher levels of pro-inflammatory M1 macrophages (P=0.04), modestly higher levels of monocytes (P=0.08), and lower levels of neutrophils (P=0.04) – typically considered immunosuppressive – compared with IDH2-mutant gliomas. No differences were observed in levels of B cells, dendritic cells, NK cells, or T cell subsets (Treg, CD4+, CD8+). IDH2-mutant gliomas were enriched for hallmark oligodendroglioma mutations (TERT promoter, CIC, FUBP1), while IDH1-mutant gliomas were enriched for hallmark astrocytoma mutations (ATRX, TP53). However, associations with tumor-infiltrating immune cells persisted after excluding 1p/19q co-deleted oligodendroglioma from analyses. GSEA revealed upregulation of the microglial TYROBP signaling pathway, the microglial phagocytic pathway, and of Type II Interferon signaling in IDH1-mutant gliomas versus IDH2-mutant gliomas. CONCLUSIONS Although IDH2 mutations are generally thought to function similarly to IDH1 mutations, we observe differences in tumor-infiltrating immune cells across groups. IDH2-mutant gliomas appeared to have a more immunosuppressive tumor microenvironment than their IDH1-mutant counterparts. Early-phase immunotherapy trials should consider covariate-adaptive randomization approaches to equally allocate IDH2-mutant gliomas across treatment arms.

Clinical and Molecular Features of Patients with Gliomas Harboring Idh1 Non-Canonical Mutations: A Systematic Review and Meta-Analysis.

Purpose The canonical isocitrate dehydrogenase 1 R132 mutation (IDH1 R132) is the most frequent mutation among IDH mutated gliomas. Non-canonical IDH1 mutations or IDH2 mutations are unusual and their clinical and biological role is still unclear.Methods We performed a systematic review and meta-analysis aimed to assess the clinical role of IDH non-canonical mutations. ResultsOverall, we selected 13 of 3513 studies reporting data of 4007 patients with a diagnosis of grade 2 and grade 3 including 3091 patients with a molecularly proven IDH1 or IDH2 mutation. Patients with non-canonical IDH1 mutations were younger and presented a higher DNA methylation level as compared to those with canonical IDH1 R132H alteration. The overall incidence of non-canonical IDH1 mutations was 7.9% (95% CI 5.4 – 10.7%) in patients with IDH mutated gliomas. There was no statistical difference in terms of incidence between patients with grade 2 or grade 3 glioma. Patients with non-canonical IDH mutations had a lower rate of 1p19q codeletion (risk difference: 31%, 95% CI 23 -38%) and presented a significantly prolonged survival (pooled-HR 0.47, 95% CI, 0.28-0.81) as compared to those with IDH1 R132H mutation. Conclusion Non-canonical IDH1 mutations occur in 7.9% of IDH mutated gliomas and recognize a specific subgroup of patients with an improved survival despite a lower rate of 1p19q codeletion. Data about the type of IDH mutation should be collected in clinical practice and within interventional trials as this could be a critical variable for an improved patient’s stratification and selection.

Association of TP53 Alteration with Tissue Specificity and Patient Outcome of IDH1-Mutant Glioma

Since the initial discovery of recurrent isocitrate dehydrogenase 1 (IDH1) mutations at Arg132 in glioma, IDH1 hotspot mutations have been identified in cholangiocarcinoma, chondrosarcoma, leukemia, and various other types of cancer of sporadic incidence. Studies in glioma and leukemia have helped promote the theory that IDH1 mutations are an oncogenic event that drives tumorigenesis in general. Through bioinformatic analysis of more than 45,000 human pan-cancer samples from three independent datasets, we show here that IDH1 mutations are rare events in human cancer but are exclusively prevalent in WHO grade II and grade III (lower-grade) glioma. Interestingly, alterations in the tumor-suppressor gene TP53 (tumor protein p53) co-occur significantly with IDH1 mutations and show a tendency of exclusivity to IDH2 mutations. The co-occurrence of IDH1 mutation and TP53 alteration is widespread in glioma, particularly in those harboring IDH1R132H, IDH1R132G, and IDH1R132S, whereas co-occurrence of IDH1R132C and TP53 alteration can be found sporadically in other cancer types. In keeping with the importance of p53 in tumor suppression, TP53 status is an independent predictor of overall survival irrespective of histological and molecular subgroups in lower-grade glioma. Together, these results indicate tissue specificity of IDH1 hotspot mutation and TP53 alteration and the importance of TP53 status as a predictor of patient outcome in lower-grade glioma.

5-Hydroxymethylcytosine Loss in Conjunctival Melanoma

Aims: Conjunctival and cutaneous melanoma partially share similar clinical and molecular backgrounds. As 5-hydroxymethylcytosine (5-hmC) loss has been demonstrated in cutaneous melanoma, we decided to assess if similar changes were occurring in conjunctival melanoma. Methods: 5-methylcytosine (5-mC), 5-hmC and TET2 were respectively identified by immunohistochemistry and RNA ISH in 40 conjunctival nevi and 37 conjunctival melanomas. Clinicopathological correlations were established. Results: 5-mC, TET2 and 5-hmC were respectively identified in 67.5%, 95% and 100% of conjunctival nevi and in 81.1%, 35.1% and 54% of conjunctival melanomas. A significant 5-hmC and TET2 loss was identified in conjunctival melanoma comparing to nevus, as well as a significant correlation between TET2 and 5-hmC expression. In the melanomas, 5-hmC expression was only significantly associated with local lymphatic invasion, but not with other clinicopathological parameters. There was a correlation between TET2 expression and the localization of the tumors. 5-mC expression was not associated with any clinicopathological parameters. Conclusions: We identified a significant 5-hmC loss in conjunctival melanoma similar to cutaneous melanoma. This loss may possibly be attributed to TET2 loss or IDH1 mutations. 5-hmC loss in conjunctival melanoma may help in the differential diagnosis between atypical conjunctival nevus and conjunctival melanoma.

Opposed Interplay between IDH1 Mutations and the WNT/β-Catenin Pathway: Added Information for Glioma Classification

Gliomas are the main common primary intraparenchymal brain tumor in the central nervous system (CNS), with approximately 7% of the death caused by cancers. In the WHO 2016 classification, molecular dysregulations are part of the definition of particular brain tumor entities for the first time. Nevertheless, the underlying molecular mechanisms remain unclear. Several studies have shown that 75% to 80% of secondary glioblastoma (GBM) showed IDH1 mutations, whereas only 5% of primary GBM have IDH1 mutations. IDH1 mutations lead to better overall survival in gliomas patients. IDH1 mutations are associated with lower stimulation of the HIF-1α a, aerobic glycolysis and angiogenesis. The stimulation of HIF-1α and the process of angiogenesis appears to be activated only when hypoxia occurs in IDH1-mutated gliomas. In contrast, the observed upregula aggressiveness and angiogenesis. Molecular pathways of the malignancy process are involved in early stages of WNT/β-catenin pathway-activated-gliomas, and this even under normoxic conditions. IDH1 mutations lead to decreased activity of the WNT/β-catenin pathway and its enzymatic targets. The opposed interplay between IDH1 mutations and the canonical WNT/β-catenin pathway in gliomas could participate in better understanding of the observed evolution of different tumors and could reinforce the glioma classification.