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Introduction Indolent systemic mastocytosis (ISM) is a rare clonal mast cell disease driven by the KIT D816V mutation in nearly all patients. Patients with ISM can present with debilitating acute and chronic cutaneous, gastrointestinal, neurocognitive, and systemic symptoms caused by the release of inflammatory mediators from abnormal mast cells. In some patients, symptoms are not adequately controlled with best supportive care (BSC) medications. Elenestinib (BLU-263) is a novel, investigational, oral, next-generation tyrosine kinase inhibitor that potently and selectively inhibits KIT D816V with limited central nervous system penetration and pharmacokinetics (PK) that support once daily dosing. HARBOR (NCT04910685) is a randomized, double-blind, placebo-controlled, phase 2/3 study assessing efficacy and safety of elenestinib in patients with ISM. Methods Eligible adult patients with ISM, confirmed following central review of bone marrow (BM) pathology, clinical, and laboratory findings per World Health Organization criteria and a moderate-to-severe symptom score based on minimum mean total symptom score (TSS) of the ISM-Symptom Assessment Form (ISM-SAF©2018), were stratified by baseline serum tryptase (<20 ng/mL vs ≥20 ng/mL) and randomly assigned 3:1 to elenestinib 25 mg, 50 mg, or 100 mg once daily + BSC (“elenestinib”) or placebo + BSC (“placebo”). The primary objective of Part 1 was to determine the recommended dose based on safety, PK, and pharmacodynamics. Secondary endpoints included changes in biomarkers of disease burden (serum tryptase, KIT D816V variant allele fraction [VAF], and BM mast cells) and ISM-SAF TSS. Three additional open-label PK groups enrolled patients at 50 mg, 75 mg, and 100 mg to further characterize PK and safety. Results As of data cutoff on July 3, 2023, a total of 122 patients with ISM have received their assigned treatment in Part 1 of the study; 39 were blinded and randomized to elenestinib or placebo, and 83 were treated with open-label elenestinib in the PK groups (21 patients at 50 mg, 34 patients at 75 mg, and 28 patients at 100 mg). Baseline demographics were similar to those reported for the general ISM population. After 12 weeks of therapy, symptom improvement was observed for all dose cohorts, and symptom reduction by TSS was greater for patients on elenestinib versus placebo in the blinded portion of Part 1. Patients receiving elenestinib at 25 mg, 50 mg, and 100 mg doses showed reduction (mean percent) from baseline for tryptase (-15.4%, -50.9%, and -68.4% vs 3.3%, respectively) and KIT D816VVAF (-37.5%, -70.3%, and -77.0% vs -2.5%, respectively) as compared to placebo. Similar reductions in TSS and disease-related biomarkers were observed in the open-label PK cohorts. After a median treatment duration of 35.3 weeks, elenestinib was well-tolerated at all dose levels. There were no treatment-related serious adverse events and no treatment-related adverse events that led to drug discontinuation. Conclusion Elenestinib at all tested doses demonstrated beneficial effects on disease-related symptoms and biomarkers of mast cell burden in this large and maturing cohort of patients with ISM with a moderate-to-severe symptom burden. Elenestinib was well tolerated across all dose levels with a promising early benefit-risk profile in ISM. These preliminary findings will inform dosing for the planned Part 2 of HARBOR, which will examine elenestinib versus placebo in a randomized, blinded, placebo-controlled setting.

Purpose: Advances in targeted therapeutics for histiocytic neoplasms have led to a growing survivor population, especially for Erdheim-Chester disease (ECD), Langerhans cell histiocytosis (LCH), and Rosai-Dorfman disease (RDD). This growing population is at risk of adverse health-related quality of life (HRQoL) as a result of the disease or treatments received. Patient-reported outcomes in this population remain understudied, and we aim to define their HRQoL using a validated tool. Methods: We enrolled patients from 2 histiocytosis centers and an international conference from Aug 2022-April 2023 to complete the PROMIS © (Patient-Reported Outcomes [PROs] Measurement Information System) 29+2 profile v2.1, which captures 8 domains of physical/mental health and functioning. Domains are reported as T-scores, with 50 being the general population mean. We calculated summary T-scores for Physical Health (PH) and Mental Health (MH), and differences of 3 from general population were considered clinically meaningful. We then used these T-scores to calculate each patient's PROMIS-Preference (PROPr) score, which is a health-utility score that measures overall HRQoL. A mean PROPr score difference of 0.4 from the US population mean of 0.52 was considered meaningful. We ran independent-samples t-tests to examine differences in PH/MH summary scores and PROPr between sub-cohorts. Finally, we performed a multinomial logistic regression analysis to identify factors associated with worse scores, and calculated odds ratios (OR) for each factor. Results: We included a total of 77 participants. Specific diagnoses included ECD (n=33, 42.9%), LCH (n=21, 27.3%), RDD (n=19, 24.7%), and other/unknown (n=4, 5.2%). Median age at diagnosis was 50y (9-79) and at survey was 54y (18-82), with a median 4 year difference between diagnosis and survey completion. Racial demographics included white (n=64, 83.1%), Black (n=12, 15.6%), and Asian (n=1, 1.3%). 4 patients (5.2%) identified as having a Hispanic ethnicity. Disease extent included unifocal (n=13, 16.9%), single system multifocal (ss-M, n=8, 10.4%), single system lung LCH (ss-L, n=3, 3.9%), or multisystem (n=53, 68.8%) disease. The most commonly involved organs included bone (n=44, 57.1%), kidney (n=24, 31.2%), skin (n=24, 31.2%), CNS (n=24, 31.2%), and pituitary (n=19, 24.7%). PH and MH summary scores were lower in various diagnostic categories as compared with the US population, and PROPr scores were reduced in all diagnostic categories. Bone involvement was associated with worse PH (-6.16, 95%CI -10.81, -1.52, [p=0.005]), MH (-7.96, 95%CI -12.48, -3.44, [p=<0.001]), and PROPr (-0.184, 95%CI -0.313, -0.056, [p=0.003]) scores. CNS involvement was associated with worse PH (-4.78, 95%CI -9.14, -0.42, [p=0.016]). We initially constructed a multinomial regression model using diagnosis, race, age at survey completion, and CNS and bone involvement. This model was not statistically significant, and in particular, diagnosis and age did not significantly contribute to the model. We then removed diagnosis and age and constructed a new model using the remaining variables, which was statistically significant for all 3 scores (p<0.05). We found that factors associated with worse PH score were disease involvement of bone (OR=6.19, 95%CI 1.88, 20.43 [p=0.003]) and CNS (OR=10.36, 95%CI 2.01, 53.39 [p=0.005] Figure 2). Factors associated with worse MH scores included female sex (OR=4.12, 95%CI 1.24, 13.66 [p=0.021]) and CNS involvement (OR=10.74, 95%CI 2.47, 46.79 [p=0.002]). Having race/ethnic group other than white/Non-Hispanic or Black was associated with improved MH. However, as this group had only 4 members, the significance of this is uncertain. Finally, CNS involvement was found to be associated with worse odds of having a low PROPr score (OR=10.46, 95%CI 2.17, 50.37 [p=0.003]). Conclusions: Several PROs were worse in patients with histiocytic neoplasms as compared with the general population. We further found that CNS involvement was independently associated with worse HRQoL, regardless of the diagnosis type. Additionally, female sex was associated with worse MH scores, and bone involvement with worse PH scores. PROPr score was particularly low among patients with ECD. Future research is warranted to assess the impact of treatments on HRQoL, as well as the economic loss resulting from loss of productivity as highlighted by low PROPr scores.

Introduction: BCMA-directed CAR-T and Bispecific T-cell engager (BiTE) therapies have shown remarkable overall response rates in heavily pretreated patients with relapsed/refractory multiple myeloma (RRMM). This has led to the approval of idecabtagene vicleucel, ciltacabtagene autoleucel and teclistamab by the FDA, EMA and other regulatory agencies. We performed a global survey on accessibility, practice patterns, and toxicity management of commercially available CAR-T and BiTE therapies. Methods: An online survey was completed by clinicians attending the International Myeloma Society's Immune Effector Cell Therapies in Multiple Myeloma Workshop, in-person or virtually, made available for 30 days after the meeting held in March 2023, Boston, MA. Results: 87 clinicians from 16 countries completed the survey, most practicing in an academic practice (86%) and in an urban environment (89%). Sixty-four percent of the respondents practice in North America followed by Europe (25.3%) including Germany, United Kingdom, Ireland, Italy, Netherlands, Spain, France, Greece, and Cyprus, and 6.9% from Asia and 3.4% from Australia. Seventy-seven percent reported CAR-T cell therapy was approved in their country with 44.8% treating 1-5 patients and 14.9% treating >5 patients per month; 67% reported BiTE therapy was approved in their country with 14.9% treating >5 patients per month. Of evaluable responses (n = 40), 62% administered CAR-T therapy inpatient and 15% administered CAR-T therapy outpatient ≥ 50% of the time. Length of time between decision to treat with CAR-T therapy to infusion was 6-12 weeks for 42% of responders and <6 weeks for only 20%. Most (75%) reported inpatient administration of BiTE therapy step-up dosing; 17.5% reported outpatient step-up dosing administered ≥ 50% of the time. Use of institutional or practice SOPs for CAR-T and BiTE therapy patient selection was reported by 85% and 58%, respectively, with the factors influencing SOP outlined in Table 1. Of available CAR-T therapies, 53% prefer cilta-cel and 23% reported CAR-T therapy preference depended most on patients' co-morbidities/frailty (89%), timing of next available apheresis (67%), age (56%), CNS disease (44%) and other factors. Maintenance therapy after CAR-T therapy was reportedly used by 25% and 5% of respondents in 1-10% and 11-50% of their patients, respectively, to “maintain level of response achieved” (50%) or “achieve a deeper level of response” (25%). About half (43%) of the respondents reported using an SOP or particular criteria for secondary Hemophagocytic Lympho-Histiocytosis/Macrophage Activation Syndrome/CAR-related-HLH (sHLH/MAS/CarHLH) management that varied between the use of ASTCT Working Group IEC associated HLH-like syndrome Criteria (47%) (Hines 2023), CARTOX HLH Criteria (24%) (Neelapu 2017) and HLH-2004 criteria (6%). Tocilizumab was used as cytokine release syndrome (CRS) prophylaxis only by one responder. Keppra neurologic prophylaxis was used by 47.5% and 15% of responders for CAR-T and BiTE therapy, respectively. Delayed neurotoxicity with CAR-T was reported in 1-5% of patients by 57.5% of responders and 6-10% of patients by 15% of responders; most common manifestations were other movement/neuromuscular disorder (62%), nerve palsy (55%), and Parkinsonism (45%). Infectious prophylaxis was used to protect against HSV (92.5%), PJP (90%), bacterial pathogens (55%), fungal pathogens (60%), and IVIG (77.5%). However, criteria for infectious prophylaxis use varies widely incorporating IgG levels, infectious history, CD4+ count, B-cell aplasia and cytopenias (48.1 - 88.9%). Most respondents (46.3 - 86.5%) reported completing an infectious work-up including CMV, EBV, Hep B/C, and HIV ( Table 2). Conclusions: Trends of CAR-T and BiTE therapy use and patterns of concurrent prophylactic and supportive care in MM vary widely among academic centers across the globe, demonstrating a need for further understanding of toxicity pathogenesis, toxicity management and consistent guidelines. This survey also demonstrates the great unmet need for access beyond urban centers among the international myeloma community. Prospective studies and claims data analysis should be utilized to evaluate the longitudinal cost of care, quality of life, duration of response and management of infectious disease, neurological or related complications of CAR-T and bispecific TCE therapies.

Background: Menin, a protein involved in transcriptional regulation, plays a role in the genesis of multiple cancers. Preclinical data from BMF-219, an investigational, highly selective, oral small-molecule inhibitor of menin, show sustained potent abrogation of menin-dependent oncogenic signaling. BMF-219 is the first and only covalent menin inhibitor in clinical development and is being evaluated in multiple hematologic malignancies, solid tumors, and diabetes mellitus. COVALENT-101 (NCT05153330) is a Phase I dose-escalation and -expansion study of BMF-219 in R/R AL (Cohort 1), DLBCL (Cohort 2), MM (Cohort 3), and CLL (Cohort 4). Here we report preliminary safety, PK and anticancer activity data from Cohort 1 (AL). Methods: Doses of BMF-219 are escalated independently for each indication, initially in single-subject cohorts followed by a “3 + 3” design. Eligible patients (pts) include adults with R/R AL ineligible for standard therapy. Initially pts were enrolled agnostic to molecular status. A subsequent amendment introduced quotas for KMT2Ar (MLL1r), NPM1 and other known menin-dependent mutations: CEBP/A, MLL1-PTD, MN1, NUP98, NUP214, PICALM-AF10, SETBP1. Prior exposure to reversible menin inhibitor therapy is permitted. Subjects receive BMF-219 daily for continuous 28-day cycles until progression/intolerability. There are 2 parallel dose-escalation arms: pts not taking (Arm A) or taking (Arm B) moderate or strong CYP3A4 inhibitors. The study is ongoing and accruing in the escalation. Expansion cohorts will enroll pts to obtain further safety and efficacy data at the OBD/RP2D. Results: As of data cutoff of 7/24/2023, 26 pts with R/R AL (24 AML; 2 ALL) are enrolled; 7 remain on study treatment. Baseline characteristics include 17(65%) males and 9(35%) females with a median age of 57.5 years (range 33-84). There is a median of 4 (range 1-8) prior lines of therapy and 11 (42%) with prior HSCT(s). Six pts (23%) had KMT2Ar, 3 (12%) KMT2A-PTD, 4 (15%) NPM1, and 13 (50%) WT for KMT2A and NPM1. Dosing began with single-patient cohorts at 100 mg QD (Arm A) and 25 mg QD (Arm B) and has been escalated through 4 dose levels. Thus far, pts have been dosed up to 500 mg QD (Arm A) and 125 mg QD (Arm B). BMF-219 exposures were comparable between arms, with ~2-4-fold higher exposures observed with co-administration of a moderate or strong CYP3A4 inhibitor. At the highest dose (DL4) in which PK was evaluated, Arm A (500 mg QD) and Arm B (125 mg QD), pts on average achieved ~50% of target exposure (2000 ng*hr/mL) with some pts surpassing it. Higher QD dosing or corresponding BID dosing is expected to achieve desired exposure. BMF-219 has generally been well tolerated with no DLTs observed and no discontinuations due to treatment-related toxicities. No related QTc prolongation was observed. At the time of data cutoff, 23 of 26 pts were included in the safety population. Common TRAEs (≥10%) include vomiting 13% (3) and Differentiation Syndrome (DS) 13% (3). No Grade 5 TRAEs were reported. The only common Grade ≥3 TRAE (≥5%) was DS 13% (3). The efficacy evaluable population includes AML pts who meet the following criteria: dosed at or near predicted efficacious dose (500 mg or above [Arm A]; 125 mg or above [Arm B]), had known menin-dependent mutations, and completed at least one scheduled response assessment (or had a minimum of 7 doses if discontinued prematurely). Thus far, 2 of 5 efficacy evaluable patients achieved a complete remission (1 CR; 1 CRi) and both continue BMF-219 treatment. Patient A: 39/M, NUP98-NSD1, ECOG=0, 500 mg QD, Arm A, 4 prior lines of treatment including intensive chemotherapy and allo-HSCT. At C1D27, marrow blasts were reduced to 6% from 13% at study entry. The patient achieved CR at C2D28 with 0% blasts.Patient B: 70/F, NPM1m, ECOG=1, 125 mg QD, Arm B, 1 prior line of treatment with decitabine and an investigational agent. At C1D28, marrow blasts were reduced to 34% from 52% at study entry. The patient achieved CRi with 3% blasts at C2D28. Conclusion: BMF-219 is generally well tolerated with no DLT observed (and able to be taken with and without CYP3A4 inhibitors) with no pts discontinuing therapy due to toxicity. BMF-219 dose escalation is ongoing and approaching target exposure. BMF-219 demonstrates early signs of clinical activity in different genomic subgroups. The trial is ongoing and includes enrollment for pts diagnosed with AL, DLBCL, MM and CLL.

Introduction A single ide-cel infusion showed significantly longer median progression-free survival (PFS) vs std regimens (13.3 vs 4.4 months [mo], HR 0.49, 95% CI 0.38-0.65, P < 0.001) with deep, durable responses in heavily pretreated TCE RRMM at an interim analysis (IA) of KarMMa-3 (NCT03651128); safety data were consistent with prior studies (Rodríguez-Otero et al. NEJM 2023). Ide-cel benefits were consistent across pts in high-risk subgroups and across 2-4 prior lines of therapy (Tx). Results of the preplanned final PFS analysis of KarMMa-3 with 12.3 mo additional follow-up are reported. Methods In the phase 3 KarMMa-3 trial, pts with RRMM who received 2-4 prior regimens, including an immunomodulatory agent, proteasome inhibitor, and daratumumab, and were refractory to last regimen were randomized 2:1 to ide-cel or a std regimen (DPd, DVd, IRd, Kd, or EPd). In the ide-cel arm, pts could receive ≤ 1 cycle of optional bridging Tx for disease control. Pts in the std regimens arm could receive ide-cel after confirmed disease progression (PD). The primary endpoint was IRC-assessed PFS in the ITT population; final PFS was planned to be analyzed with ~289 events. Key secondary endpoints were IRC-assessed overall response rate (ORR) and overall survival (OS); other secondary endpoints included complete response rate (CRR), duration of response (DOR), minimal residual disease (MRD) status, time to next anti-myeloma Tx (TTNT; time from randomization to next anti-myeloma Tx [MTx]), event-free survival (EFS; time from randomization to first PD, next MTx or any-cause death, whichever is first), PFS2 (time from randomization to second objective PD or any-cause death, whichever is first), safety, and health-related quality of life (QOL). Results Of 386 randomized pts (ide-cel, n = 254; std regimens, n = 132), 225 received ide-cel and 126 received a std regimen. Baseline characteristics were generally balanced. Median follow-up from randomization to data cutoff (April 28, 2023) was 30.9 mo (range 12.7-47.8). Ide-cel significantly improved median PFS (95% CI) vs std regimens (13.8 [11.8-16.1] vs 4.4 [3.4-5.8] mo), representing a 51% reduced risk of PD or death (HR 0.49, 95% CI 0.38-0.63; Figure); 18 mo PFS rates were 41% vs 19%, respectively. Ide-cel significantly improved ORR vs std regimens (71% vs 42%) with deeper (CRR 44% vs 5%; ≥CR and MRD negative status [sensitivity level 10 -5], 22% vs 1%), more durable responses (median DOR 16.6 vs 9.7 mo; Table). PFS and ORR benefits of ide-cel vs std regimens were consistent with the IA. Interim OS will be included in the presentation. In pts who received ide-cel (n = 225) or a std regimen (n = 126), median PFS (95% CI) was 15.7 (12.5-18.9) vs 4.4 (3.4-5.8) mo, respectively. In the ITT population, median TTNT, EFS, and PFS2 were numerically longer with ide-cel vs std regimens. Median (range) TTNT was 20.9 (16.6-24.2) vs 7.0 (5.3-8.5) mo. Median (95% CI) EFS was 13.3 (11.3-15.7) vs 3.9 (3.0-5.3) mo. Median PFS2 (95% CI) was 23.5 (18.4-27.9) vs 16.7 (12.2-20.3) mo; ide-cel was next MTx in 70 (53%) pts in the std regimens arm. In the treated population, grade (gr) 3/4 infections occurred in 66/249 (27%) pts in the ide-cel arm vs 25/126 (20%) in the std regimens arm. In the ide-cel safety population, any gr cytokine release syndrome occurred in 197/225 (88%) pts, gr ≥ 3 in 11 (5%); median time to first onset was 1 d (1-14), median duration was 4 d (1-51). Any gr investigator-identified neurotoxicity occurred in 34/225 (15%) pts, gr ≥ 3 in 7 (3%); median time to onset was 3 d (range 1-317); median duration was 2.5 d (range 1-252). Ide-cel continued to demonstrate durable, clinically meaningful improvements in pt-reported outcomes, including symptoms, functioning, and QOL vs std regimens. Conclusions In this final PFS analysis of KarMMa-3, significantly longer PFS was maintained with ide-cel; PD or death risk reduced by 51%; responses were deeper and more durable vs std regimens. CRR with ide-cel increased since the IA, indicating a deepening response, but were unchanged with std regimens. A single ide-cel infusion vs continuous treatment with std regimens resulted in longer median TTNT and PFS2, indicating improved long-term disease control. The ide-cel safety profile was consistent with previous reports, with no parkinsonism or Guillain-Barré syndrome reported. These data continue to support use of ide-cel in pts with TCE RRMM. Study support 2seventy bio and Celgene, a Bristol-Myers Squibb Company.

Abstract Background PARP-1 has a well-established role in DNA repair. PARP-1 selective inhibitors are a new subclass of PARPi that offer potential for improved tolerability. NMS-03305293 (NMS-293) is an oral, brain-penetrant PARP-1 selective inhibitor with strong antitumor activity in BRCA mutated preclinical models. Furthermore, NMS-293 is synergistic with temozolomide (TMZ) in glioblastoma mouse models. Methods Two phase I/I-II dose-escalation/expansion studies assessed safety, tolerability, and preliminary antitumor activity of NMS-293. Both are actively recruiting. In PARPA-293-001 (NCT04182516), NMS-293 was administered orally, ranging from 20 mg (QD) to 160 mg (BID) for 21 or 28 days on 28-day cycle in adult patients with advanced/metastatic, relapsed/refractory solid tumors who have exhausted standard treatment options. In PARPA-293-002 (NCT04910022), NMS-293 was administered in a range of doses orally, QD or BID on days 1-7 plus TMZ 150mg/m2 QD on days 1-5 in repeated 28-day cycle in adult patients with recurrent diffuse gliomas. Tumor responses were measured by investigator-assessed RANO criteria. Results The unpooled safety database at the data-cut-off (02-AUG-23), includes 45 patients in PARPA-001 and 21 patients in PARPA-002. PARPA-001 showed an MTD of 100 mg BID for 28 days on a 28-day cycle, a dose with meaningful PK relative to preclinical activity. PARPA-002 dose finding is ongoing with no DLTs as of cutoff date. The most frequent (≥10%) any-grade treatment related adverse events (TRAEs) in PARPA-001 were reversible QTcF prolongation, nausea, asthenia, decreased appetite and vomiting, mainly mild/moderate. In PARPA-002, with discontinuous NMS-293 plus TMZ, no G≥3 TRAEs were reported. The most frequent (≥10%) any-grade TRAEs were: nausea, fatigue, vomiting, decreased appetite, and platelet count decreased, mainly G1 adverse events. Overall, no dose-dependent trends of myelosuppression have been observed. 14 recurrent glioma patients across dose levels in PARPA-002 were evaluable for tumor response. A patient with glioblastoma had confirmed partial response (PR) with duration 7.6+ weeks, remaining on treatment at cutoff date. A patient with grade 3 IDH-mutant astrocytoma had unconfirmed PR with ongoing tumor shrinkage at 16.1+ weeks. A patient with glioblastoma had complete radiological disappearance of enhancing non-target lesions, remaining on treatment at cutoff date. NMS-293 PK profiles showed an increase in exposure with the dose with approximately 5 to 13 hours half-life. Conclusion NMS-293, a PARP-1 selective, brain penetrant inhibitor was well tolerated in phase I clinical trials with no dose dependent trends of myelosuppression. Furthermore, NMS-293 showed encouraging clinical activity in combination with TMZ in difficult-to-treat recurrent glioma patients. Citation Format: Marjolein Geurts, Dorothee Gramatzki, Sara Merler, Matteo Duca, Fabio Girardi, Ugur T. Sener, Domenico Roberti, Grazia Saturno, Patrizia Crivori, Alessia Montagnoli, Lisa Mahnke, Siqing Fu, Paola Gaviani, Kurt A. Jaeckle, Jian Zhang, Yehui Shi, Valentina Guarneri, Michael Weller, Sani H. Kizilbash, Martin J. van den Bent, Michele Milella, Silvia Damian. Initial results from 2 Phase I studies of NMS-03305293, a selective PARP1 inhibitor [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 LB_A12.

Abstract Oligodendroglioma is characterized by oligodendrocyte-like histology, mutation in the IDH genes, along with codeletion of chromosome arms 1p and 19q. Treatment for oligodendrogliomas combines surgery, followed by observation, and chemotherapy and/or radiotherapy when tumors progress. Most oligodendrogliomas eventually recur with a more aggressive phenotype, leading to patient mortality but molecular mechanisms remain poorly understood. To investigate the molecular trajectory of oligodendroglioma, we collected more than 270 longitudinal samples from over 130 oligodendroglioma patients, to perform whole genome or whole exome sequencing, bulk RNA, and single-nucleus RNA sequencing (n = 30 samples). Common mutations in IDH1/2, TERT promoter, CIC, and FUBP1 were observed. About half of the CIC and FUBP1 mutations occurred in the initial sample and persisted stably throughout recurrence. The majority of PIK3CA and PIK3R1 mutations were either shared or present in recurrences only implicating the PI3K pathway in oligodendroglioma recurrence. Mutational signature analysis revealed 34.5% of tumors treated with alkylating agents acquired SBS11/SBS31 associated hypermutation. By integrating signatures with clonality estimates, we approximated the timing of mutational processes and found that clonal timings of treatment related mutations correlate with the treatment administration date. We found that aging signature-related mutations were mostly clonal, and treatment signature-related mutations were more likely to be sub-clonal, supporting the late emergence of these mutations following treatment. We observed increased somatic copy number alterations in oligodendroglioma recurrences, reflected in notable chromosome 4 losses. Associating treatment with snRNAseq derived cellular states, we observed a significant increase in the fraction of proliferating stem-like cells in the hypermutator versus non-hypermutator recurrent samples. These findings shed light on the molecular changes occurring in oligodendrogliomas following treatment and provide insights that may aid in targeting treatment resistance.