Aurora Kinase A inhibition enhances DNA damage and tumor cell death with 131I-MIBG therapy in high-risk neuroblastoma

Background

Neuroblastoma is the most common extra-cranial pediatric solid tumor. 131I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical highly specific for neuroblastoma tumors, providing potent radiotherapy to widely metastatic disease. Aurora kinase A (AURKA) plays a role in mitosis and stabilization of the MYCN protein in neuroblastoma. Here we explore whether AURKA inhibition potentiates a response to MIBG therapy.

Results

Using an in vivo model of high-risk neuroblastoma, we demonstrated a marked combinatorial effect of 131I-MIBG and alisertib on tumor growth. In MYCN amplified cell lines, the combination of radiation and an AURKA A inhibitor increased DNA damage and apoptosis and decreased MYCN protein levels.

Conclusion

The combination of AURKA inhibition with 131I-MIBG treatment is active in resistant neuroblastoma models and is a promising clinical approach in high-risk neuroblastoma.

Re-irradiation of recurrent IDH-wildtype glioblastoma in the bevacizumab and immunotherapy era: Target delineation, outcomes and patterns of recurrence

Introduction and background

While recurrent glioblastoma patients are often treated with re-irradiation, there is limited data on the use of re-irradiation in the setting of bevacizumab (BEV), temozolomide (TMZ) re-challenge, or immune checkpoint inhibition (ICI). We describe target delineation in patients with prior anti-angiogenic therapy, assess safety and efficacy of re-irradiation, and evaluate patterns of recurrence.

Materials and methods

Patients with a histologically confirmed diagnosis of glioblastoma treated at a single institution between 2013 and 2021 with re-irradiation were included. Tumor, treatment and clinical data were collected. Logistic and Cox regression analysis were used for statistical analysis.

Results

One hundred and seventeen recurrent glioblastoma patients were identified, receiving 129 courses of re-irradiation. In 66 % (85/129) of cases, patients had prior BEV. In the 80 patients (62 %) with available re-irradiation plans, 20 (25 %) had all T2/FLAIR abnormality included in the gross tumor volume (GTV). Median overall survival (OS) for the cohort was 7.3 months, and median progression-free survival (PFS) was 3.6 months. Acute CTCAE grade ≥ 3 toxicity occurred in 8 % of cases. Concurrent use of TMZ or ICI was not associated with improved OS nor PFS. On multivariable analysis, higher KPS was significantly associated with longer OS (p < 0.01). On subgroup analysis, patients with prior BEV had significantly more marginal recurrences than those without (26 % vs. 13 %, p < 0.01).

Conclusion

Re-irradiation can be safely employed in recurrent glioblastoma patients. Marginal recurrence was more frequent in patients with prior BEV, suggesting a need to consider more inclusive treatment volumes incorporating T2/FLAIR abnormality.

Comparison of volumetric and 2D-based response methods in the PNOC-001 pediatric low-grade glioma clinical trial

Background

Although response in pediatric low-grade glioma (pLGG) includes volumetric assessment, more simplified 2D-based methods are often used in clinical trials. The study's purpose was to compare volumetric to 2D methods.

Methods

An expert neuroradiologist performed solid and whole tumor (including cyst and edema) volumetric measurements on MR images using a PACS-based manual segmentation tool in 43 pLGG participants (213 total follow-up images) from the Pacific Pediatric Neuro-Oncology Consortium (PNOC-001) trial. Classification based on changes in volumetric and 2D measurements of solid tumor were compared to neuroradiologist visual response assessment using the Brain Tumor Reporting and Data System (BT-RADS) criteria for a subset of 65 images using receiver operating characteristic (ROC) analysis. Longitudinal modeling of solid tumor volume was used to predict BT-RADS classification in 54 of the 65 images.

Results

There was a significant difference in ROC area under the curve between 3D solid tumor volume and 2D area (0.96 vs 0.78, P = .005) and between 3D solid and 3D whole volume (0.96 vs 0.84, P = .006) when classifying BT-RADS progressive disease (PD). Thresholds of 15-25% increase in 3D solid tumor volume had an 80% sensitivity in classifying BT-RADS PD included in their 95% confidence intervals. The longitudinal model of solid volume response had a sensitivity of 82% and a positive predictive value of 67% for detecting BT-RADS PD.

Conclusions

Volumetric analysis of solid tumor was significantly better than 2D measurements in classifying tumor progression as determined by BT-RADS criteria and will enable more comprehensive clinical management.

Inaugural Results of the Individualized Screening Trial of Innovative Glioblastoma Therapy: A Phase II Platform Trial for Newly Diagnosed Glioblastoma Using Bayesian Adaptive Randomization

PURPOSE

The Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) is a phase II platform trial that uses response adaptive randomization and genomic profiling to efficiently identify novel therapies for phase III testing. Three initial experimental arms (abemaciclib [a cyclin-dependent kinase [CDK]4/6 inhibitor], neratinib [an epidermal growth factor receptor [EGFR]/human epidermal growth factor receptor 2 inhibitor], and CC-115 [a deoxyribonucleic acid-dependent protein kinase/mammalian target of rapamycin inhibitor]) were simultaneously evaluated against a common control arm. We report the results for each arm and examine the feasibility and conduct of the adaptive platform design.

PATIENTS AND METHODS

Patients with newly diagnosed O6-methylguanine-DNA methyltransferase-unmethylated glioblastoma were eligible if they had tumor genotyping to identify prespecified biomarker subpopulations of dominant glioblastoma signaling pathways (EGFR, phosphatidylinositol 3-kinase, and CDK). Initial random assignment was 1:1:1:1 between control (radiation therapy and temozolomide) and the experimental arms. Subsequent Bayesian adaptive randomization was incorporated on the basis of biomarker-specific progression-free survival (PFS) data. The primary end point was overall survival (OS), and one-sided P values are reported. The trial is registered with ClinicalTrials.gov (identifier: NCT02977780).

RESULTS

Two hundred thirty-seven patients were treated (71 control; 73 abemaciclib; 81 neratinib; 12 CC-115) in years 2017-2021. Abemaciclib and neratinib were well tolerated, but CC-115 was associated with ≥ grade 3 treatment-related toxicity in 58% of patients. PFS was significantly longer with abemaciclib (hazard ratio [HR], 0.72; 95% CI, 0.49 to 1.06; one-sided P = .046) and neratinib (HR, 0.72; 95% CI, 0.50 to 1.02; one-sided P = .033) relative to the control arm but there was no PFS benefit with CC-115 (one-sided P = .523). None of the experimental therapies demonstrated a significant OS benefit (P > .05).

CONCLUSION

The INSIGhT design enabled efficient simultaneous testing of three experimental agents using a shared control arm and adaptive randomization. Two investigational arms had superior PFS compared with the control arm, but none demonstrated an OS benefit. The INSIGhT design may promote improved and more efficient therapeutic discovery in glioblastoma. New arms have been added to the trial.

Noninvasive molecular subtyping of pediatric low-grade glioma with self-supervised transfer learning

Purpose

To develop and externally validate a scan-to-prediction deep-learning pipeline for noninvasive, MRI-based BRAF mutational status classification for pLGG.

Materials and Methods

We conducted a retrospective study of two pLGG datasets with linked genomic and diagnostic T2-weighted MRI of patients: BCH (development dataset, n=214 [60 (28%) BRAF fusion, 50 (23%) BRAF V600E, 104 (49%) wild-type), and Child Brain Tumor Network (CBTN) (external validation, n=112 [60 (53%) BRAF-Fusion, 17 (15%) BRAF-V600E, 35 (32%) wild-type]). We developed a deep learning pipeline to classify BRAF mutational status (V600E vs. fusion vs. wildtype) via a two-stage process: 1) 3D tumor segmentation and extraction of axial tumor images, and 2) slice-wise, deep learning-based classification of mutational status. We investigated knowledge-transfer and self-supervised approaches to prevent model overfitting with a primary endpoint of the area under the receiver operating characteristic curve (AUC). To enhance model interpretability, we developed a novel metric, COMDist, that quantifies the accuracy of model attention around the tumor.

Results

A combination of transfer learning from a pretrained medical imaging-specific network and self-supervised label cross-training (TransferX) coupled with consensus logic yielded the highest macro-average AUC (0.82 [95% CI: 0.70-0.90]) and accuracy (77%) on internal validation, with an AUC improvement of +17.7% and a COMDist improvement of +6.4% versus training from scratch. On external validation, the TransferX model yielded AUC (0.73 [95% CI 0.68-0.88]) and accuracy (75%).

Conclusion

Transfer learning and self-supervised cross-training improved classification performance and generalizability for noninvasive pLGG mutational status prediction in a limited data scenario.

Genetic architecture of the acute and persistent immune cell response after radiation exposure

Hematologic toxicity is a common side effect of multimodal cancer therapy. Nearly all animal studies investigating the causes of radiotherapy-induced hematologic toxicity use inbred strains with limited genetic diversity and do not reflect the diverse responses observed in humans. We used the population-based Collaborative Cross (CC) mouse resource to investigate the genetic architecture of the acute and persistent immune response after radiation exposure by measuring 22 immune parameters in 1,720 CC mice representing 35 strains. We determined relative acute and persistent radiation resistance scores at the individual strain level considering contributions from all immune parameters. Genome-wide association analysis identified quantitative trait loci associated with baseline and radiation responses. A cross-species radiation resistance score predicted recurrence-free survival in medulloblastoma patients. We present a community resource of immune parameters and genome-wide association analyses before and after radiation exposure for future investigations of the contributions of host genetics on radiosensitivity.

Expert-level pediatric brain tumor segmentation in a limited data scenario with stepwise transfer learning

Purpose

Artificial intelligence (AI)-automated tumor delineation for pediatric gliomas would enable real-time volumetric evaluation to support diagnosis, treatment response assessment, and clinical decision-making. Auto-segmentation algorithms for pediatric tumors are rare, due to limited data availability, and algorithms have yet to demonstrate clinical translation.

Methods

We leveraged two datasets from a national brain tumor consortium (n=184) and a pediatric cancer center (n=100) to develop, externally validate, and clinically benchmark deep learning neural networks for pediatric low-grade glioma (pLGG) segmentation using a novel in-domain, stepwise transfer learning approach. The best model [via Dice similarity coefficient (DSC)] was externally validated and subject to randomized, blinded evaluation by three expert clinicians wherein clinicians assessed clinical acceptability of expert- and AI-generated segmentations via 10-point Likert scales and Turing tests.

Results

The best AI model utilized in-domain, stepwise transfer learning (median DSC: 0.877 [IQR 0.715-0.914]) versus baseline model (median DSC 0.812 [IQR 0.559-0.888]; p<0.05). On external testing (n=60), the AI model yielded accuracy comparable to inter-expert agreement (median DSC: 0.834 [IQR 0.726-0.901] vs. 0.861 [IQR 0.795-0.905], p=0.13). On clinical benchmarking (n=100 scans, 300 segmentations from 3 experts), the experts rated the AI model higher on average compared to other experts (median Likert rating: 9 [IQR 7-9]) vs. 7 [IQR 7-9], p<0.05 for each). Additionally, the AI segmentations had significantly higher (p<0.05) overall acceptability compared to experts on average (80.2% vs. 65.4%). Experts correctly predicted the origins of AI segmentations in an average of 26.0% of cases.

Conclusions

Stepwise transfer learning enabled expert-level, automated pediatric brain tumor auto-segmentation and volumetric measurement with a high level of clinical acceptability. This approach may enable development and translation of AI imaging segmentation algorithms in limited data scenarios.

Feasibility of the Audio-Visual Assisted Therapeutic Ambience in Radiotherapy (AVATAR) System for Anesthesia Avoidance in Pediatric Patients: A Multicenter Trial

PURPOSE

The Audio-Visual Assisted Therapeutic Ambience in Radiotherapy (AVATAR) system was the first published radiation therapy (RT)-compatible system to reduce the need for pediatric anesthesia through video-based distraction. We evaluated the feasibility of AVATAR implementation and effects on anesthesia use, quality of life, and anxiety in a multicenter pediatric trial.

METHODS AND MATERIALS

Pediatric patients 3 to 10 years of age preparing to undergo RT at 10 institutions were prospectively enrolled. Children able to undergo at least 1 fraction of RT using AVATAR without anesthesia were considered successful (S). Patients requiring anesthesia for their entire treatment course were nonsuccessful (NS). The PedsQL3.0 Cancer Module (PedsQL) survey assessed quality of life and was administered to the patient and guardian at RT simulation, midway through RT, and at final treatment. The modified Yale Preoperative Anxiety Scale (mYPAS) assessed anxiety and was performed at the same 3 time points. Success was evaluated using the χ2 test. PedsQL and mYPAS scores were assessed using mixed effects models with time points evaluated as fixed effects and a random intercept on the subject.

RESULTS

Eighty-one children were included; median age was 7 years. AVATAR was successful at all 10 institutions and with photon and proton RT. There were 63 (78%) S patients; anesthesia was avoided for a median of 20 fractions per patient. Success differed by age (P = .04) and private versus public insurance (P < .001). Both patient (P = .008) and parent (P = .006) PedsQL scores significantly improved over the course of RT for patients aged 5 to 7. Anxiety in the treatment room decreased for both S and NS patients over RT course (P < .001), by age (P < .001), and by S versus NS patients (P < .001).

CONCLUSIONS

In this 10-center prospective trial, anesthesia avoidance with AVATAR was 78% in children aged 3 to 10 years, higher than among age-matched historical controls (49%; P < .001). AVATAR implementation is feasible across multiple institutions and should be further studied and made available to patients who may benefit from video-based distraction.

Children's Oncology Group's 2023 blueprint for research: Central nervous system tumors

Tumors of the central nervous system (CNS) are a leading cause of morbidity and mortality in the pediatric population. Molecular characterization in the last decade has redefined CNS tumor diagnoses and risk stratification; confirmed the unique biology of pediatric tumors as distinct entities from tumors that occur in adulthood; and led to the first novel targeted therapies receiving Food and Drug Administration (FDA) approval for children with CNS tumors. There remain significant challenges to overcome: children with unresectable low-grade glioma may require multiple prolonged courses of therapy affecting quality of life; children with high-grade glioma have a dismal long-term prognosis; children with medulloblastoma may suffer significant short- and long-term morbidity from multimodal cytotoxic therapy, and approaches to improve survival in ependymoma remain elusive. The Children's Oncology Group (COG) is uniquely positioned to conduct the next generation of practice-changing clinical trials through rapid prospective molecular characterization and therapy evaluation in well-defined clinical and molecular groups.

Children's Oncology Group's 2023 blueprint for research: Radiation oncology

Radiation oncology is an integral part of the multidisciplinary team caring for children with cancer. The primary goal of our committee is to enable the delivery of the safest dose of radiation therapy (RT) with the maximal potential for cure, and to minimize toxicity in children by delivering lower doses to normal tissues using advanced technologies like intensity-modulated RT (IMRT) and proton therapy. We provide mentorship for y ators and are actively involved in educating the global radiation oncology community. We are leaders in the effort to discover novel radiosensitizers, radioprotectors, and advanced RT technologies that could help improve outcomes of children with cancer.

Serum miRNA-based signature indicates radiation exposure and dose in humans: A multicenter diagnostic biomarker study

PURPOSE

Mouse and non-human primate models showed that serum miRNAs may be used to predict the biological impact of radiation doses. We hypothesized that these results can be translated to humans treated with total body irradiation (TBI), and that miRNAs may be used as clinically feasible biodosimeters.

METHODS

To test this hypothesis, serial serum samples were obtained from 25 patients (pediatric and adults) who underwent allogeneic stem-cell transplantation and profiled for miRNA expression using next-generation sequencing. miRNAs with diagnostic potential were quantified with qPCR and used to build logistic regression models with lasso penalty to reduce overfitting, identifying samples drawn from patients who underwent total body irradiation to a potentially lethal dose.

RESULTS

Differential expression results were consistent with previous studies in mice and non-human primates. miRNAs with detectable expression in this and two prior animal sets allowed for distinction of the irradiated from non-irradiated samples in mice, macaques and humans, validating the miRNAs as radiation-responsive through evolutionarily conserved transcriptional regulation mechanisms. Finally, we created a model based on the expression of miR-150-5p, miR-30b-5p and miR-320c normalized to two references and adjusted for patient age with an AUC of 0.9 (95%CI:0.83-0.97) for identifying samples drawn after irradiation; a separate model differentiating between high and low radiation dose achieved AUC of 0.85 (95%CI: 0.74-0.96).

CONCLUSIONS

We conclude that serum miRNAs reflect radiation exposure and dose for humans undergoing TBI and may be used as functional biodosimeters for precise identification of people exposed to clinically significant radiation doses.

Phase I study of a novel glioblastoma radiation therapy schedule exploiting cell-state plasticity

BACKGROUND

Glioblastomas comprise heterogeneous cell populations with dynamic, bidirectional plasticity between treatment-resistant stem-like and treatment-sensitive differentiated states, with treatment influencing this process. However, current treatment protocols do not account for this plasticity. Previously, we generated a mathematical model based on preclinical experiments to describe this process and optimize a radiation therapy fractionation schedule that substantially increased survival relative to standard fractionation in a murine glioblastoma model.

METHODS

We developed statistical models to predict the survival benefit of interventions to glioblastoma patients based on the corresponding survival benefit in the mouse model used in our preclinical study. We applied our mathematical model of glioblastoma radiation response to optimize a radiation therapy fractionation schedule for patients undergoing re-irradiation for glioblastoma and developed a first-in-human trial (NCT03557372) to assess the feasibility and safety of administering our schedule.

RESULTS

Our statistical modeling predicted that the hazard ratio when comparing our novel radiation schedule with a standard schedule would be 0.74. Our mathematical modeling suggested that a practical, near-optimal schedule for re-irradiation of recurrent glioblastoma patients was 3.96 Gy × 7 (1 fraction/day) followed by 1.0 Gy × 9 (3 fractions/day). Our optimized schedule was successfully administered to 14/14 (100%) patients.

CONCLUSIONS

A novel radiation therapy schedule based on mathematical modeling of cell-state plasticity is feasible and safe to administer to glioblastoma patients.

TMET-07. MOLECULAR MECHANISM OF EXQUISITE SENSITIVITY OF DIFFUSE MIDLINE GLIOMA TO DE NOVO PYRIMIDINE BIOSYNTHESIS

Diffuse midline glioma (DMG) is a lethal pediatric brain cancer in dire need for therapeutic breakthroughs. To identify intrinsic addictions and therapeutic targets for DMG, we conducted a genome-wide k¬¬¬¬nockout CRISPR screen that identified de novo pyrimidine biosynthesis pathway as a targetable dependency. Since pyrimidine nucleotides can be synthesized by salvage and de novo pathways, identification of the latter as a dependency indicated a prominent role of de novo pathway in establishing the pyrimidine nucleotide pool in DMG. We investigated the molecular mechanism underlying this dependency using metabolic tracing of 15N-glutamine and genetic approaches. We report that DMG cells derive the majority of UMP (70%) through de novo synthesis, along with significantly elevated flux through the pyrimidine degradation pathway. High flux of 15N- labeled UMP through pyrimidine degradation in DMGs suggests that substrates (uridine and uracil) required for pyrimidine nucleotide salvage are limited, thus enhancing the dependency on de novo biosynthesis. To further confirm the causal role of pyrimidine degradation in driving de novo pathway dependency in DMG, we knocked down DPYD, the enzyme catalyzing the first committed step in pyrimidine degradation, using inducible shRNAs. Knockdown of DPYD diminished sensitivity of DMGs to de novo pathway inhibition as it rescued UMP pools and resultant DNA damage. Conversely, overexpression of DPYD in adult glioblastomas enhanced their sensitivity to de novo pyrimidine synthesis inhibition which was accompanied by greater depletion of UMP and induction of DNA damage. Consistent with this mechanism, we observed downregulation of DPYD in DMGs that acquired resistance to antagonists of de novo pyrimidine synthesis. Taken together, we have uncovered DPYD as a predictive biomarker of sensitivity to de novo pyrimidine synthesis inhibitors.

BIOM-37. EVALUATION OF TEMPORALIS MUSCLE THICKNESS WITH TOXICITY AND SURVIVAL IN GLIOBLASTOMA PATIENTS RECEIVING CHEMORADIATION

BACKGROUND

Treatment-related toxicity is common in patients with glioblastoma (GBM) receiving chemotherapy and radiotherapy (RT). Temporalis muscle thickness (TMT) is a biomarker associated with sarcopenia and worse clinical outcomes in GBM, however its relation to treatment toxicity is less studied. We hypothesize that TMT may predict toxicity and survival in GBM patients.

METHODS

We reviewed consecutive patients with IDH-wildtype GBM treated from 2014-2019 at a single academic center. TMT was retrospectively assessed on T1-weighted MRI scans and dichotomized based upon previously validated sex-specific cutoff values. TMT was measured on baseline MRI scan at time of diagnosis. Cox regression multivariable analysis (MVA) was used to assess survival.

RESULTS

We evaluated 351 patients with median age of 60y (range 20-94) and median follow-up of 14mo. Most patients were male (59%), baseline KPS &gt;70 (95%), and MGMT unmethylated (55%). After maximal safe resection, most patients received standard (90%) or hypofractionated (10%) RT with concurrent systemic therapy (89%). On MVA, baseline low TMT (HR 1.93, p=0.01), age &gt;65y, baseline KPS, and MGMT-unmethylated status were associated with worse OS. On MVA, baseline low TMT (HR 1.95, p=0.01), age &gt;65y, MGMT-unmethylated status, and discontinuing systemic therapy were associated with worse profession-free survival (PFS). 21 patients did not complete anticipated treatment course of chemoradiation and adjuvant systemic therapy due to toxicity, primarily thrombocytopenia, associated with worse OS on MVA (HR 1.99, p&lt; 0.01). Low TMT was associated with higher risk of stopping treatment due to adverse events (OR 5.25, p&lt; 0.01) independent of age, sex, extent of resection, RT dose on MVA.

CONCLUSION

Baseline low TMT was associated with worse PFS and OS, and it was associated with treatment interruption due to treatment toxicity in GBM patients. While further validation is needed, TMT may help identify patients who will benefit from aggressive symptom management or treatment deintensification.

CTNI-53. PNOC014: PHASE IB STUDY RESULTS OF DAY101(TOVORAFENIB) FOR CHILDREN WITH LOW-GRADE GLIOMAS (LGGS) AND OTHER RAS/RAF/MEK/ERK PATHWAY-ACTIVATED TUMORS

BACKGROUND

Pharmacokinetic modeling for previously reported phase 1A data of pan-RAF inhibitor DAY101 in RAS/RAF/MEK/ERK pathway-altered tumors suggested a correlation between higher doses and improved efficacy without clear safety data. The protocol was amended to explore differential dosing across different body surface areas (BSA).

METHODS

Eligible patients were &lt; 25 years old with radiographically recurrent/progressive RAS/RAF/MEK/ERK pathway-altered tumors. We applied a novel modification of a TITE-BOIN design to determine recommended phase 2 dosing of oral, weekly DAY101 in evaluable patients within two BSA subgroups: ≤ 1.5 m2 or &gt; 1.5 m2. Target toxicity probability was closest to 20%. We tested 420 and 530 mg/m2. Dose limiting toxicities (DLTs) were determined within Cycle 1. Evaluable patients had either ‘complete’ or ‘partial’ information. Complete information meant patient had a DLT or received 3 of 4 planned doses with no DLT. Partial information meant patient received only 1 or 2 doses or did not complete the DLT observation period. Three patients with complete information at a given dose level were required before dose escalation. The primary endpoint driving dose escalation was time from start of Cycle 1 to first DLT or, if no DLT, time from start of Cycle 1 to minimum of date of last contact or end of Cycle 1.

RESULTS

We treated 35 eligible patients: 21 KIAA1549:BRAF-, 9 BRAFV600E-, 4 novel RAF- and one FGFR1-altered tumors. Histologically, cohort included 30 LGGs, 4 high grade gliomas and 1 soft tissue sarcoma. There were 6 DLTs: 3 in each BSA subgroup, all at 530 mg/m2/dose, all grade 3, and 5 known side effects ( 2 fatigue, 3 rash, 1 menorrhagia).

CONCLUSIONS

Oral weekly DAY101 is well tolerated. The TITE model recommends 530 mg/m2/dose PO weekly for patients with BSA &lt; 1.5m2 and 420 mg/m2/dose PO weekly for patients with BSA &gt;1.5m2.

LGG-52. Volumetry-based response characterization of recurrent pediatric low-grade gliomas in PNOC clinical Neuro-oncology trials

BACKGROUND: Endpoints in clinical trials using novel treatments are evaluated by RANO criteria, which provide an estimate of tumor size from two-dimensional measurements along the most prominent axial slice. However, pediatric low-grade gliomas (pLGG) commonly have variegated shapes with solid and cystic components, potentially resulting in misevaluation of true tumor volume and thus, ultimately, trial outcome. OBJECTIVES: We aim to characterize treatment response through volumetric assessment of progressive/recurrent pLGGs treated with single-agent everolimus on PNOC001 clinical trial. We seek to identify clinically relevant criteria that provide added value to response assessment beyond 2D measurements. METHODS: In a cohort of 44 patients we performed 3D-segmentation of solid, cystic and whole tumor within our PACS-framework and compared results to previously carried-out central imaging review by RANO criteria which had yielded 15 PD, 27 SD, 2 PR and 0 CR. RESULTS: 8 tumors were solid only and 36 had a mixed solid-cystic appearance. When evaluating the entire tumor (i.e. solid and cystic components combined) and using the same RANO cutoff criteria, one case changed from PR to SD, one changed from SD to PR, 3 changed from SD to PD, and 7 changed from PD to SD, resulting in an overall discordance of 27% of cases. CONCLUSION: We propose that incorporation of volumetrics into response assessment provides additional and potentially more accurate information beyond RANO-based measurements. It is crucial to note that the above-reported changes represent numerical discrepancies as opposed to true-to-reality changes in clinical outcome. Determining representative thresholds for the deployment of volumetric measures in clinical trials will be critical. Future work will include data from the PNOC002 clinical trial and evaluate inter-reader agreement and reader discordance. With the availability of PACS-based 3D-tools in neuroradiology practice, well-defined volumetric criteria could be incorporated prospectively into treatment response analysis in clinical trials.

Patient specific distortion detection and mitigation in MR images used for stereotactic radiosurgery

Objective. In MRI-based radiation therapy planning, mitigating patient-specific distortion with standard high bandwidth scans can result in unnecessary sacrifices of signal to noise ratio. This study investigates a technique for distortion detection and mitigation on a patient specific basis. Approach. Fast B0 mapping was performed using a previously developed technique for high-resolution, large dynamic range field mapping without the need for phase unwrapping algorithms. A phantom study was performed to validate the method. Distortion mitigation was validated by reducing geometric distortion with increased acquisition bandwidth and confirmed by both the B0 mapping technique and manual measurements. Images and contours from 25 brain stereotactic radiosurgery patients and 95 targets were analyzed to estimate the range of geometric distortions expected in the brain and to estimate bandwidth required to keep all treatment targets within the ±0.5 mm iso-distortion contour. Main Results. The phantom study showed, at 3 T, the technique can measure distortions with a mean absolute error of 0.12 mm (0.18 ppm), and a maximum error of 0.37 mm (0.6 ppm). For image acquisition at 3 T and 1.0 mm resolution, mean absolute distortion under 0.5 mm in patients required bandwidths from 109 to 200 Hz px−1 for patients with the least and most distortion, respectively. Maximum absolute distortion under 0.5 mm required bandwidths from 120 to 390 Hz px−1. Significance. The method for B0 mapping was shown to be valid and may be applied to assess distortion clinically. Future work will adapt the readout bandwidth to prospectively mitigate distortion with the goal to improve radiosurgery treatment outcomes by reducing healthy tissue exposure.

Wee1 kinase inhibitor adavosertib with radiation in newly diagnosed diffuse intrinsic pontine glioma: A Children's Oncology Group phase I consortium study

Background

Children with diffuse intrinsic pontine gliomas (DIPG) have a dismal prognosis. Adavosertib (AZD1775) is an orally available, blood-brain barrier penetrant, Wee1 kinase inhibitor. Preclinical efficacy against DIPG is heightened by radiation induced replication stress.

Methods

Using a rolling six design, 7 adavosertib dose levels (DLs) (50 mg/m2 alternating weeks, 50 mg/m2 alternating with weeks of every other day, 50 mg/m2, then 95, 130, 160, 200 mg/m2) were assessed. Adavosertib was only given on days of cranial radiation therapy (CRT).The duration of CRT (54 Gy over 30 fractions; 6 weeks) constituted the dose limiting toxicity (DLT) period. Endpoints included tolerability, pharmacokinetics, overall survival (OS) and peripheral blood γH2AX levels as a marker of DNA damage.

Results

A total of 46 eligible patients with newly diagnosed DIPG [median (range) age 6 (3-21) years; 52% female] were enrolled. The recommend phase 2 dose (RP2D) of adavosertib was 200 mg/m2/d during days of CRT. Dose limiting toxicity included ALT elevation (n = 1, DL4) and neutropenia (n = 1, DL7). The mean Tmax, T1/2 and Clp on Day 1 were 2 h, 4.4 h, and 45.2 L/hr/m2, respectively. Modest accumulation of adavosertib was observed comparing day 5 versus day 1 AUC0-8h (accumulation ratio = 1.6). OS was 11.1 months (95% CI: 9.4, 12.5) and did not differ from historical control.

Conclusion

Adavosertib in combination with CRT is well tolerated in children with newly diagnosed DIPG, however, compared to historical controls, did not improve OS. These results can inform future trial design in children with high-risk cancer.

Gender, Productivity, and Philanthropic Fundraising in Academic Oncology

BACKGROUND

Philanthropic donations are important funding sources in academic oncology but may be vulnerable to implicit or explicit biases toward women. However, the influence of gender on donations has not been assessed quantitatively.

METHODS

We queried a large academic cancer center's development database for donations over 10 years to the sundry funds of medical and radiation oncologists. Types of donations and total amounts for medical oncologists and radiation oncologists hired prior to April 1, 2018 (allowing ≥2 years on faculty prior to query), were obtained. We also obtained publicly available data on physician/academic rank, gender, specialty, disease site, and Hirsch-index (h-index), a metric of productivity.

RESULTS

We identified 127 physicians: 64% men and 36% women. Median h-index was higher for men (31; range, 1-100) than women (17; range, 3-77; P=.003). Men were also more likely to have spent more time at the institution (median, 15 years; range, 2-43 years) than women (median, 12.5 years; range, 3-22 years; P=.025). Those receiving donations were significantly more likely to be men (70% vs 30%; P=.034). Men received significantly higher median amounts ($259,474; range, $0-$29,507,784) versus women ($37,485; range, $0-$7,483,726; P=.019). On multivariable analysis, only h-index and senior academic rank were associated with donation receipt, and only h-index with donation amount.

CONCLUSIONS

We found significant gender disparities in receipt of philanthropic donations on unadjusted analyses. However, on multivariable analyses, only productivity and rank were significantly associated with donations, suggesting gender disparities in productivity and promotions may contribute to these differences.

CTNI-40. EVALUATING FEASIBILITY AND EFFICIENCY OF PHASE II ADAPTIVE PLATFORM TRIAL DESIGNS BASED ON THE INDIVIDUALIZED SCREENING TRIAL OF INNOVATIVE GLIOBLASTOMA THERAPY (INSIGhT) EXPERIENCE

BACKGROUND

The Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) is a phase II platform trial with Bayesian adaptive randomization and deep genomic profiling to more efficiently test experimental agents in newly diagnosed glioblastoma and to prioritize therapies for late-stage testing.

METHODS

In the ongoing INSIGhT trial, patients with newly diagnosed MGMT-unmethylated glioblastoma are randomized to the control arm or one of three experimental therapy arms (CC-115, abemaciclib, and neratinib). The control arm therapy is radiotherapy with concomitant and adjuvant temozolomide, and primary endpoint is overall survival. Randomization has been adapted based on Bayesian estimation of biomarker-specific probability of treatment impact on progression-free survival (PFS). All tumors undergo detailed molecular sequencing, and this is facilitated with the companion ALLELE protocol. To evaluate feasibility of this approach, we assessed the status of this ongoing trial.

RESULTS

Since INSIGhT was activated 4.3 years ago, it has expanded to include 12 sites across the United States. A total of 247 patients have been enrolled. Randomization probabilities have been repeatedly adjusted over time based upon early PFS results to alter the randomization ratio from standard 1:1:1:1 randomization. All three arms have completed accrual and efficacy estimates are available based upon comparison to the common control arm in context of relevant biomarkers. There are 87 patients alive and in follow-up, and there are ongoing plans to add additional arms to evaluate further treatments in the future.

CONCLUSION

The INSIGhT trial demonstrates that a multi-center Bayesian adaptive platform trial is a feasible and effective approach to help prioritize therapies and biomarkers for newly diagnosed GBM. The trial has maintained robust accrual, and the simultaneous testing of multiple agents, sharing a common control arm and adaptive randomization serve as features to increase trial efficiency relative to traditional clinical trial designs.

PATH-16. EVALUATION OF SEX-BASED DIFFERENCES IN CLINICAL OUTCOMES AND TUMOR GENOMICS IN PATIENTS WITH NEWLY DIAGNOSED IDH-WILDTYPE GLIOBLASTOMA RECEIVING CHEMORADIATION

BACKGROUND

We evaluated sex-based differences in clinical outcomes and tumor genomics in patients with newly-diagnosed GBM.

METHODS

We reviewed 665 IDH-wild type GBM patients with Karnofsky Performance Status (KPS) ≥60 treated at our institution from 2010-2019 including; 585 patients with targeted exome sequencing of 447 cancer associated genes (OncoPanel). Deleterious mutations were defined as homozygous deletions or loss of function mutations of known tumor suppressors (as reported in TCGA, ≥ 3 times in the COSMIC database, or predicted as “damaging” in SIFT and/or “probably damaging” in Polyphen 2) or known oncogenic mutations in proto-oncogenes (reported in TCGA or ≥ 3 times in COSMIC).

RESULTS

There were 384 (57.7%) males and 281 (42.3%) females. Median OS was 22.5 months for females and 19.3 months for males (hazard ratio [HR] 0.81, 95% CI 1.03-1.48, p = 0.02). On multivariable analysis adjusted for age, KPS ≥90, extent of resection, and MGMT methylation status, female sex (adjusted hazard ratio 0.78, 95% CI [0.64-0.95], p = 0.015) was associated with improved OS. Superior OS in females was observed in MGMT-unmethylated patients (HR 0.69, 95% CI [0.54-0.90], p = 0.005) but not MGMT-methylated patients. Thirteen genes were deleteriously altered in ≥5% of our cohort: CDK4 (12.1% male vs. 7.8% female), CDKN2A (46.5% vs. 45.7%), CDKN2B (41.8% vs. 43.3%), EGFR (34.7% vs. 40.0%, MTAP (18.2% vs. 18.8%), NF1 (11.5% vs. 9.4%), PTEN (28.2% vs. 29.8%), TP53 (28.2% vs. 30.2%), RB1 (5.6% vs. 6.5%), MDM4 (6.2% vs. 5.7%), ATM (5.9% vs. 3.7%), MDM2 (7.4% vs. 4.1%), PIK3R1 (6.2% vs. 4.1%). There were no differences in frequency of mutations in these individual genes between males and females (χ 2 [1, N=585] = 0.05-2.86, p = 0.09-0.86).

CONCLUSIONS

Female sex is associated with improved survival. We did not identify sex-based differences in deleterious genomic alterations amongst commonly altered genes in GBM.

CTNI-05. PRELIMINARY RESULTS OF THE NERATINIB ARM IN THE INDIVIDUALIZED SCREENING TRIAL OF INNOVATIVE GLIOBLASTOMA THERAPY (INSIGHT): A PHASE II PLATFORM TRIAL USING BAYESIAN ADAPTIVE RANDOMIZATION

BACKGROUND

EGFR is amplified in over 50% of glioblastoma and 20-30% have EGFRvIII mutations. Neratinib is a potent inhibitor of EGFR/HER2 approved for metastatic HER2+ breast cancer. To efficiently evaluate the potential impact of neratinib on overall survival (OS) in newly-diagnosed glioblastoma and to simultaneously develop information regarding potential genomic biomarker associations, neratinib was included as an arm on the Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) trial. INSIGhT is a phase II platform trial using response adaptive randomization and deep genomic profiling to more efficiently test experimental agents in MGMT unmethylated glioblastoma and accelerate identification of novel therapies for phase III testing. Initial randomization was equal between neratinib, control, and two other experimental arms but subsequent randomization was adapted based on efficacy as determined by progression-free survival (PFS). We report preliminary results for the neratinib arm.

METHODS

Patients with newly diagnosed MGMT-unmethylated glioblastoma were randomized to receive either radiotherapy with concomitant and adjuvant temozolomide or standard radiochemotherapy followed by adjuvant neratinib (240 mg daily). Treatment continued until progression or development of unacceptable toxicities. The primary endpoint was OS. Association between neratinib efficacy and EGFR amplification was also investigated.

RESULTS

There were 144 patients (70 control; 74 neratinib). Neratinib was reasonably well-tolerated with no new toxicity signals identified. PFS was compared (HR 0.84; p=0.38, logrank test – not significant) between the neratinib (median 6.05 months) and control (median 5.82 months) arms. For patients EGFR pathway activation the PFS HR was 0.53 (p-value=0.03 – significant, median PFS: neratinib, 6.21 months, control, 5.26 months). However, there was no significant improvement in OS in EGFR amplified/mutated patients (HR 1.05; p-value 0.87) between neratinib (median 14.2) compared to the control arm (median 14.6).

CONCLUSION

Neratinib prolonged PFS in the EGFR positive subpopulation but there was no overall PFS benefit, or any OS improvement.

Update on Radiation Therapy for Central Nervous System Tumors

Radiation therapy has long been a critical modality of treatment of patients with central nervous system tumors, including primary brain tumors, brain metastases, and meningiomas. Advances in radiation technology and delivery have allowed for more precise treatment to optimize patient outcomes and minimize toxicities. Improved understanding of the molecular underpinnings of brain tumors and normal brain tissue response to radiation will allow for continued refinement of radiation treatment approaches to improve clinical outcomes for brain tumor patients. With continued advances in precision and delivery, radiation therapy will continue to be an important modality to achieve optimal outcomes of brain tumor patients.

Outcomes after first relapse of childhood intracranial ependymoma

BACKGROUND

Ependymoma is the third most common malignant CNS tumor in children. Despite multimodal therapy, prognosis of relapsed ependymoma remains poor. Approaches to therapy for relapsed ependymoma are varied. We present a single-institution retrospective review of the outcomes after first relapse of intracranial ependymoma in children.

PROCEDURE

We performed a retrospective, IRB-approved chart review of patients with recurrent intracranial ependymoma treated at Dana-Farber/Boston Children's Cancer and Blood Disorders Center from 1990 to 2019.

RESULTS

Thirty-four patients with relapsed intracranial ependymoma were identified. At initial diagnosis, 11 patients had supratentorial disease, 22 with posterior fossa disease and one with metastatic disease. Median time-to-first relapse was 14.9 months from initial diagnosis (range 1.4-52.5). Seven patients had metastatic disease at first relapse. Gross total resection (GTR) was associated with improved 5-year progression-free survival (PFS) relative to subtotal resection (STR) and no surgery (p = .005). Localized disease at relapse was associated with improved 5-year overall survival (OS) when compared to metastatic disease (p = .02). Irradiation at first relapse seemed to delay progression but was not associated with statistically prolonged PFS or OS. Tumor location, histology, and chromosomal 1q status did not impact outcome at first relapse, although available molecular data were limited making definitive conclusions difficult. Median time-to-second relapse was 10 months (range 0.7-124). Five-year PFS and OS after first relapse were 19.9% and 45.1%, respectively. Median PFS and OS were 10.0 and 52.5 months after first relapse, respectively.

CONCLUSIONS

Relapsed intracranial ependymoma has a poor prognosis despite multimodal therapy. Novel therapeutic strategies are desperately needed for this disease.

HGG-38. DE NOVO PYRIMIDINE SYNTHESIS INHIBITION INDUCES REPLICATION CATASTROPHE MEDIATED CELL DEATH IN DIFFUSE MIDLINE GLIOMA

Diffuse midline gliomas (DMG) are aggressive and lethal pediatric brain tumors that cannot be cured by conventional therapeutic modalities. Using a genome wide CRISPR screen we identified the de novo pyrimidine biosynthesis pathway as a metaboilic vulnerability in DMGs. BAY2402234 is a small molecule inhibitor of DHODH -a rate liminting enzyme in the de novo pyrimidine biosynthesis pathway. BAY2402234 induces cell death in DMG cells at low nanomolar concentrations while sparing adult glioblastoma cells and normal astrocytes. Further investigations revealed drammatic reduction in cellular UMP pools, the precursor for all pyrimidine nucleotides, after DHODH inhibition, specifically in DMG cells. Cytotoxicity of DHODH inhibition in DMG cells is rescued by exogenous uridine, supporting UMP depletion as the mechanism underlying DMG cell death and also showing that cell death is an “on target” response to BAY2402234. Cell death induced by BAY2402234 is a consequence of replication fork stalling as evident by accumulation of chromatin-bound RPA foci and g-H2AX. Stalled replication forks eventually collapse, resulting in replication catastrophy and apoptosis. Cytotoxic effects of DHODH inhibition are further exacerbated by inhibition of the intra-S checkpoint protein, ATR. Combined treatment of DMG cells with DHODH and ATR inhibitors resulted in enhanced accumulation of chromatin-bound RPA, g-H2AX, replication fork collapse and apoptosis. Importantly, in vivo studies verify that both BAY2402234 (DHODHi), and BAY1895344 (ATRi), cross the blood-brain barrier, accumulate in the brain at therapeutically relevant concentrations, and induce DNA damage in intracranial DMG xenografts in mice. Taken together, our studies have identified DHODH inhibition as a DMG-specific vulnerability resulting in cell death; the mechanism of DHODHi-induced cell death led us to identify combined inhibition of DHODH and ATR as a synergistic therapy against DMG tumors.

Gliomas, germ cell tumors, and craniopharyngioma

This report summarizes the current multimodality treatment approaches for children with low- and high-grade gliomas, germinoma, and nongerminomatous germ cell tumors, and craniopharyngiomas used in the Children's Oncology Group (COG) and the International Society of Pediatric Oncology (SIOP). Treatment recommendations are provided in the context of historical approaches regarding the roles of surgery, radiation, and chemotherapy. Future research strategies for these tumors in both COG and SIOP are also discussed.

Temozolomide-induced hypermutation is associated with distant recurrence and reduced survival after high-grade transformation of low-grade IDH-mutant gliomas

BACKGROUND

Chemotherapy improves overall survival after surgery and radiotherapy for newly diagnosed high-risk IDH-mutant low-grade gliomas, but a proportion of patients treated with temozolomide (TMZ) will develop recurrent tumors with TMZ-induced hypermutation. We aimed to determine the prevalence of TMZ-induced hypermutation at recurrence and prognostic implications.

METHODS

We sequenced recurrent tumors from 82 patients with initially low-grade IDH-mutant gliomas who underwent re-operation and correlated hypermutation status with grade at recurrence and subsequent clinical outcomes.

RESULTS

Hypermutation was associated with high-grade disease at the time of re-operation (OR 12.0 95% CI 2.5-115.5, p=0.002) and was identified at transformation in 57% of recurrent LGGs previously exposed to TMZ. After anaplastic (grade III) transformation, hypermutation was associated with shorter survival on univariate and multivariate analysis (HR 3.4, 95% CI 1.2-9.9, p=0.024), controlling for tumor grade, subtype, age, and prior radiotherapy. The effect of hypermutation on survival after transformation was validated in an independent, published dataset. Hypermutated (HM) tumors were more likely to develop discontiguous foci of disease in the brain and spine (p=0.003). To estimate the overall incidence of high-grade transformation among low-grade IDH-mutant tumors, data from a phase II trial of TMZ for LGG were analyzed. 8-year transformation-free survival was 53.8% (95% CI 42.8-69.2) and 61% of analyzed transformed cases were HM.

CONCLUSIONS

TMZ-induced hypermutation is a common event in transformed LGG previously treated with TMZ, and is associated with worse prognosis and development of discontiguous disease after recurrence. These findings impact tumor classification at recurrence, prognostication, and clinical trial design.

DDRE-32. THERAPEUTIC TARGETING OF A NOVEL METABOLIC ADDICTION IN DIFFUSE MIDLINE GLIOMA

Diffuse midline glioma (DMG) is a uniformly fatal pediatric cancer that is in need of urgent “outside the box” therapeutic approaches. Recent studies show that tumor cells adapt to stresses created by oncogenic mutations and these oncogene-induced adaptations create vulnerabilities that can be exploited to therapeutic ends. To uncover these oncogene-induced vulnerabilities in DMGs we conducted a genome-wide CRIPSR knockout screen in three DMG lines. The top common DMG dependency pathway that we discovered is de novo pyrimidine biosynthesis. Under normal conditions pyrimidine nucleotide needs are met through the salvage pathway. However, in DMG tumorigenesis, pyrimidine nucleotide synthesis is rewired such that the cells become dependent on the de novo biosynthesis pathway. De novo pyrimidine synthesis is catalyzed by CAD, DHODH and UMPS; all three genes are identified as dependencies in our screen and have been validated using shRNA mediated gene knockdown. Interestingly, DMG cells did not exhibit a dependency on the de novo purine biosynthesis pathway. Using a small molecule inhibitor of DHODH, BAY2402234 [currently studied in phase I trial for myeloid malignancies (NCT03404726)], we have demonstrated and validated, (i) efficacy and specificity of de novo pyrimidine synthesis inhibition in vitro in DMG cells; (ii) de novo pyrimidine addiction is not attributable to cell proliferation; (iii) DHODH inhibition induces apoptosis by hindering replication and inciting DNA damage; (iv) DHODH and ATR inhibition act synergistically to induce DMG cell death; and (v) critical in vivo efficacy. The in vivo experiment documents that BAY2402234 crosses the blood-brain barrier, is present in the brain at therapeutically relevant concentrations, suppresses de novo pyrimidine biosynthesis in intracranial DMG tumors in mice, and prolongs survival of orthotopic DMG tumor bearing mice. Taken together, our studies have identified a novel metabolic vulnerability that can be translated for the treatment of DMG patients.

Abstract P26: Re-analyzing randomized trials with incorporation of COVID-19 risk associated with cancer therapy

Background: Cancer therapy may put patients at risk of mortality from COVID-19. The impact of abbreviated treatment courses on outcomes in the setting of COVID-19 is unknown. We incorporated COVID-19-associated risks in re-analysis of practice-defining randomized trials in oncology that compared different radiation therapy (RT) regimens. Methods: We extracted individual patient level data (IPLD) from published survival curves from randomized trials in rectal cancer (Dutch TME, TROG 01.04), early stage breast cancer (CALGB 9343, OCOG hypofractionation trial, FAST-Forward, NSABP B-39), and localized prostate cancer (CHHiP, HYPO-RT-PC). Trials were simulated with incorporation of varying risk of SARS-CoV-2 infection and mortality associated with receipt of therapy. Results: IPLD from 14,170 patients were re-analyzed. In scenarios with low COVID-19-associated risks (0.5% infection risk per fraction [IRF], 5% case fatality rate [CFR]), fractionation did not significantly affect outcomes. In locally advanced rectal cancer, short-course RT appeared preferable to long-course chemoradiation (TROG 01.04) or RT omission (Dutch TME) in most settings. While moderate hypofractionation in early stage breast cancer (OCOG hypofractionation trial) and prostate cancer (CHHiP) was not associated with survival benefits in the setting of COVID-19, more aggressive hypofractionation (FAST-Forward, HYPO-RT-PC) and accelerated partial breast irradiation (NSABP B-39) were associated with improved survival in higher risk scenarios (≥5% IRF; ≥ 20% CFR). In settings where RT can be omitted, such as favorable early stage breast cancer in the elderly (CALGB 9343), RT was associated with worse survival in higher risk pandemic scenarios (≥5% IRF, ≥ 20% CFR). Conclusions: Our framework, which can be adapted to dynamic changes in COVID-19 risk, provides a flexible, quantitative approach to assess the impact of treatment recommendations across oncology. The magnitude of potential benefit from abbreviated RT courses depends on the degree of hypofractionation and local COVID-19-associated risk. Abbreviated RT courses should be prioritized when possible and are increasingly beneficial in higher risk pandemic settings. With increased understanding and precautions against COVID-19 that can minimize risks for patients, our results support the continued use of evidence-based treatments for cancer patients in the COVID-19 era.

Citation Format: Shervin Tabrizi, Lorenzo Trippa, Daniel Cagney, Ayal A. Aizer, Shyam Tanguturi, Steffen Ventz, Geoffrey Fell, Jennifer R. Bellon, Harvey Mamon, Paul Nguyen, Anthony V. D'Amico, Daphne Haas-Kogan, Brian M. Alexander, Rifaquat Rahman. Re-analyzing randomized trials with incorporation of COVID-19 risk associated with cancer therapy [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2021 Feb 3-5. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(6_Suppl):Abstract nr P26.

Intracerebral haemorrhage in patients with brain metastases receiving therapeutic anticoagulation

BACKGROUND

Venous thromboembolism is common in patients with solid malignancies and brain metastases. Whether to anticoagulate such patients is controversial given the possibility of intracerebral haemorrhage (ICH). We evaluated the added risk of ICH in patients with brain metastases receiving therapeutic anticoagulation.

METHODS

We performed a matched, retrospective cohort study of 291 patients (100 receiving therapeutic anticoagulation vs 191 controls) with brain metastases managed at Brigham and Women's Hospital/Dana-Farber Cancer Institute between 1998 and 2015. For each patient, all MRI studies of the brain were reviewed to identify ICH. Propensity score matching and multivariable Cox regression were used to mitigate confounding.

RESULTS

The risk of ICH was comparable in patients receiving anticoagulation versus controls preanticoagulation. Postanticoagulation, we observed significant or borderline-significant associations between anticoagulation and development of any ICH (HR 1.31, 95% CI 0.96 to 1.79, p=0.09), ICH as identified by gradient echo/susceptibility-weighted imaging (HR 1.46, 95% CI 1.06 to 2.01, p=0.02), symptomatic ICH (HR 1.80, 95% CI 1.01 to 3.22, p=0.05), extralesional ICH (HR 5.82, 95% CI 1.56 to 21.7, p=0.009) and fatal ICH (HR 5.68, 95% CI 0.60 to 54.2, p=0.13). Anticoagulation was associated with differentially higher ICH risk in patients with prior ICH versus no prior ICH (HR 2.20 vs 0.68, respectively, p interaction <0.001) and symptomatic ICH risk in melanoma versus other primary malignancies (HR 6.46 vs 1.36, respectively, p interaction=0.02).

CONCLUSIONS

Anticoagulation is associated with clinically significant ICH in patients with brain metastases, especially those with melanoma or prior ICH. The indication for anticoagulation and risk of intracerebral bleeding should be considered on an individual basis among such patients.

Assessment of Simulated SARS-CoV-2 Infection and Mortality Risk Associated With Radiation Therapy Among Patients in 8 Randomized Clinical Trials

IMPORTANCE

During the COVID-19 pandemic, cancer therapy may put patients at risk of SARS-CoV-2 infection and mortality. The impacts of proposed alternatives on reducing infection risk are unknown.

OBJECTIVE

To investigate how the COVID-19 pandemic is associated with the risks and benefits of standard radiation therapy (RT).

DESIGN, SETTING, AND PARTICIPANTS

This comparative effectiveness study used estimated individual patient-level data extracted from published Kaplan-Meier survival figures from 8 randomized clinical trials across oncology from 1993 to 2014 that evaluated the inclusion of RT or compared different RT fractionation regimens. Included trials were Dutch TME and TROG 01.04 examining rectal cancer; CALGB 9343, OCOG hypofractionation trial, FAST-Forward, and NSABP B-39 examining early stage breast cancer, and CHHiP and HYPO-RT-PC examining prostate cancer. Risk of SARS-CoV-2 infection and mortality associated with receipt of RT in the treatment arms were simulated and trials were reanalyzed. Data were analyzed between April 1, 2020, and June 30, 2020.

EXPOSURES

COVID-19 risk associated with treatment was simulated across different pandemic scenarios, varying infection risk per fractions (IRFs) and case fatality rates (CFRs).

MAIN OUTCOMES AND MEASURES

Overall survival was evaluated using Cox proportional hazards modeling under different pandemic scenarios.

RESULTS

Estimated IPLD from a total of 14 170 patients were included in the simulations. In scenarios with low COVID-19-associated risks (IRF, 0.5%; CFR, 5%), fractionation was not significantly associated with outcomes. In locally advanced rectal cancer, short-course RT was associated with better outcomes than long-course chemoradiation (TROG 01.04) and was associated with similar outcomes as RT omission (Dutch TME) in most settings (eg, TROG 01.04 median HR, 0.66 [95% CI, 0.46-0.96]; Dutch TME median HR, 0.91 [95% CI, 0.80-1.03] in a scenario with IRF 5% and CFR 20%). Moderate hypofractionation in early stage breast cancer (OCOG hypofractionation trial) and prostate cancer (CHHiP) was not associated with survival benefits in the setting of COVID-19 (eg, OCOG hypofractionation trial median HR, 0.89 [95% CI, 0.74-1.06]; CHHiP median HR, 0.87 [95% CI, 0.75-1.01] under high-risk scenario with IRF 10% and CFR 30%). More aggressive hypofractionation (FAST-Forward, HYPO-RT-PC) and accelerated partial breast irradiation (NSABP B-39) were associated with improved survival in higher risk scenarios (eg, FAST-Forward median HR, 0.58 [95% CI, 0.49-0.68]; HYPO-RT-PC median HR, 0.60 [95% CI, 0.48-0.75] under scenario with IRF 10% and CFR 30%).

CONCLUSIONS AND RELEVANCE

In this comparative effectiveness study of data from 8 clinical trials of patients receiving radiation therapy to simulate COVID-19 risk and mortality rates, treatment modification was not associated with altered risk from COVID-19 in lower-risk scenarios and was only associated with decreased mortality in very high COVID-19-risk scenarios. This model, which can be adapted to dynamic changes in COVID-19 risk, provides a flexible, quantitative approach to assess the potential impact of treatment modifications and supports the continued delivery of standard evidence-based care with appropriate precautions against COVID-19.

DIPG-01. REIRRADIATION PRACTICES FOR DIFFUSE INTRINSIC PONTINE GLIOMA

INTRODUCTION

Diffuse intrinsic pontine gliomas (DIPG) are a leading cause of brain tumor deaths in children. Current standard of care includes focal radiation therapy (RT). Despite clinical improvement in the majority of patients, the effect is temporary and median survival is less than one year. The use of reirradiation and possible benefit has been reported in progressive DIPG, yet standardized approaches are lacking. We conducted an internet-based survey to assess physicians’ practices in pediatric DIPG.

METHODS

A 14-question REDCap survey regarding re-irradiation practices was emailed to 396 physicians identified through an International Pediatric Neuro-Oncology and Radiation-Oncology database.

RESULTS

Response rate was 35% overall (radiation-oncologists, 28%; pediatric oncologists, 57%). Two participants were excluded (did not treat DIPG). Participants included radiation-oncologists (62%), pediatric oncologists (7%), and pediatric neuro-oncologists (29%). Most physicians (62%) treated 1–5 DIPG patients per year, with 10% treating &gt;10/year. Reirradiation was considered a treatment option in 88%. Progressive disease or worsening clinical status were the most common reasons to consider reirradiation. The majority (84%) considered reirradiation a minimum of 6 months following initial RT. Doses varied, with median total dose 24Gy (range 12–60); 2Gy/fraction (range 1–9). Concurrent use of systemic agents with reirradiation was considered in 46%, mainly with targeted agents (37%), biologics (34%), or immunotherapy (25%). One-time reirradiation was the most common practice (71%). Interestingly, 9% of respondents would not consider reirradiation.

CONCLUSION

Although, the vast majority of physicians agree with re-irradiation as a treatment option for DIPG the total doses varied, and further clinical trials are needed.

GCT-33. A PHASE 2 TRIAL OF RESPONSE-BASED RADIATION THERAPY FOR PATIENTS WITH LOCALIZED CENTRAL NERVOUS SYSTEM GERM CELL TUMORS: A CHILDREN’S ONCOLOGY GROUP (COG) STUDY. IMPACT OF RAPID CENTRAL RADIOTHERAPY REVIEW ON RADIOTHERAPY QUALITY AND PATTERN OF FAILURE FOR NON-GERMINOMATOUS GERM CELL TUMORS

BACKGROUND

COG ACNS 1123 tested reduced radiotherapy (RT) for non-metastatic, non-germinomatous germ cell tumor (NGGCT) patients. The impact of central review on quality of RT and pattern of failure for NGGCT patients is evaluated.

METHODS

Patients who achieved a complete response (CR) or partial response (PR) to induction chemotherapy were eligible for reduced dose and field RT of 30.6 Gy whole ventricular field (WVI) and 54 Gy tumor-bed total dose. An online contouring atlas was available. Within three days of RT start, WVI plans were submitted for rapid central review. Within one week of RT completion, the complete RT record was submitted. Brain and spine MRIs of relapsed patients were centrally reviewed.

RESULTS

Between 5/2012–9/2016, 107 eligible patients were accrued and 70 met reduced RT criteria. Rapid RT review was performed for 49 (70%) of 70 patients. Forty-four (89.8%) required no modification. All modifications were completed and plans became compliant. Final central review was performed for 66 evaluable patients: 62 (94%) were per protocol; there were 2 major (1 dose and 1 target) and 2 minor deviations. Eight patients progressed; none had deviations. Median time to progression was 3.54 months (range: 1.7–19.1) from RT start. All failures had a spine component; two also had cranial component: one local progression (within the RT boost volume) and one leptomeningeal disease.

CONCLUSION

Providing an online contouring atlas and performing a rapid central review lead to high quality radiotherapy on this prospective trial. The deviations did not contribute to the pattern of failure.

EPCT-01. PHASE I STUDY OF DAY101 (TAK580) IN CHILDREN AND YOUNG ADULTS WITH RADIOGRAPHICALLY RECURRENT OR PROGRESSIVE LOW-GRADE GLIOMA (LGG)

BACKGROUND

We report a phase I study examining pharmacokinetics, safety and recommended dosage of the type 2 RAF inhibitor DAY101 in children/young adults with radiographically recurrent/progressive LGGs harboring MAPK pathway alterations.

METHODS

Applying a 3 + 3 design, patients < 18 years of age with radiographically recurrent/progressive LGG received oral DAY101 weekly for 4-week cycles up to a maximum of 2 years, if deriving clinical benefit. The starting DAY101 dosage was 280 mg/m². Dose limiting toxicities were determined after one cycle.

RESULTS

We treated nine eligible patients at 280, 350, and 420 mg/m². Eight patients had KIAA1549:BRAF fusions. One patient with NF1 did not have a biopsy. There were no DLTs. Weekly administration of DAY101 in children resulted in dose-proportional increases in C_max and AUC similar to that described in adults. A 2.2-fold mg/kg exposure difference was observed with respect to weight-based dosing and suggested a correlation to best radiographic RANO responses of 2 complete responses, 2 partial responses, 3 stable disease, and 2 progressive disease (independently-reviewed). Median time to response was 10.5 weeks (range: 8–32 weeks).

CONCLUSION

The phase 1A data provide initial pharmacokinetic parameters to describe oral weekly dosing of DAY101 in pediatric patients with radiographically recurrent/progressive LGG. Plasma exposures of DAY101 achieved in adults can be reached in pediatric patients. Oral weekly DAY101 is well-tolerated and possesses anti-tumor activity. The amended protocol will explore additional dose levels and the potential for differential dosing to achieve similar responses across a variety of BSAs.

DIPG-53. CHARACTERIZING THE ROLE OF PPM1D MUTATIONS IN THE PATHOGENESIS OF DIFFUSE INTRINSIC PONTINE GLIOMAS (DIPGS)

INTRODUCTION

We have previously found that up to 15% of all DIPGs harbor mutations in PPM1D, resulting in the expression of an activated and truncated PPM1D (PPM1Dtr). Here we evaluate the mechanisms through which PPM1Dtr enhances glioma formation and identify its associated therapeutic vulnerabilities.

METHODS

We have developed multiple in vitro and in vivo models of PPM1D-mutant DIPGs and applied quantitative proteomic and functional genomic approaches to identify pathways altered by PPM1Dtr and associated dependencies.

RESULTS

PPM1D mutations are clonal events that are anti-correlated to TP53 mutations. We find ectopic expression of PPM1Dtr to be sufficient to enhance glioma formation and to be necessary in PPM1D-mutant DIPG cells. In addition, endogenous truncation of PPM1D is sufficient to enhance glioma formation in the presence of mutant H3F3A and PDGFRA. PPM1Dtr overexpression attenuates g-H2AX formation and suppresses apoptosis and cell-cycle arrest in response to radiation treatment. Deep scale phosphoproteomics analyses reveal DNA-damage and cell cycle pathways to be most significantly associated with PPM1Dtr. Furthermore, preliminary analysis of genome-wide loss-of-function CRISPR/Cas9 screens in isogenic GFP and PPM1Dtr overexpressing mouse neural stem cells reveal differential dependency on DNA-damage response genes in the PPM1Dtr overexpressing cells. Consistent with PPM1D’s role in stabilizing MDM2, PPM1D-mutant DIPG models are sensitive to a panel of MDM2 inhibitors (Nutlin-3a, RG7388, and AMG232).

CONCLUSION

Our study shows that PPM1Dtr is both an oncogene and a dependency in PPM1D- mutant DIPG, and there are novel therapeutic vulnerabilities associated with PPM1D that may be exploited.

LGG-53. PNOC001 (NCT01734512): A PHASE II STUDY OF EVEROLIMUS FOR RECURRENT OR PROGRESSIVE PEDIATRIC LOW-GRADE GLIOMAS (pLGG)

OBJECTIVE

To estimate the 6-month Progression Free Survival (PFS6) associated with everolimus for progressive/recurrent pLGGs and to determine if activated PI3K/Akt/mTOR pathway as measured by positive phosphorylated-ribosomal protein S6 (p-RPS6) status was associated with response. METHOD: Patients 3–21 years of age with recurrent or progressive pLGG were enrolled. Everolimus was administered orally at 5 mg/m² daily. Tissue availability for molecular analysis was mandatory. Immunohistochemistry (IHC) for p-RPS6 was performed centrally. An adaptive Simon two-stage design was employed based on p-RPS6 status. Based on results of the first stage, enrollment in the second stage was either limited to pathway activated patients or open to all subjects.

RESULTS

From December 2012 to July 2019 a total of 65 subjects enrolled [median age 9 years (range 3–19); 43% female]. As of December 15, 2019 median number of treatment cycle is 8 (range 1–24); 7 patients remain on treatment. Toxicity profile is similar to published reports with rash and elevated lipid profiles as most common adverse events. PFS6 for the entire cohort is 63%; PFS6 is 64% for the activated and 61% for the non-activated patients. Central imaging review (n=52) revealed 1 partial response, 1 complete response, 33 stable disease, and 17 progressive disease at the end of study treatment. Initial molecular analysis identified BRAF alterations in 35/65 patients.

CONCLUSION

Everolimus is well tolerated and active in a subset of pLGGs. Ongoing analyses will assess predictive biomarkers of response and will be reported at the meeting.

DDRE-12. PNOC001 (NCT01734512): A PHASE II STUDY OF EVEROLIMUS FOR RECURRENT OR PROGRESSIVE PEDIATRIC LOW-GRADE GLIOMAS (pLGG)

OBJECTIVE

To estimate the 6-month Progression Free Survival (PFS6) associated with everolimus for progressive/recurrent pLGGs and to determine if activated PI3K/Akt/mTOR pathway as measured by positive phosphorylated-ribosomal protein S6 (p-RPS6) status was associated with response.

METHOD

Patients 3–21 years of age with recurrent or progressive pLGG were enrolled. Everolimus was administered orally at 5 mg/m2 daily. Tissue availability for molecular analysis was mandatory. Immunohistochemistry (IHC) for p-RPS6 was performed centrally. An adaptive Simon two-stage design was employed based on p-RPS6 status. Based on results of the first stage, enrollment in the second stage was either limited to pathway activated patients or open to all subjects.

RESULTS

From December 2012 to July 2019 a total of 65 subjects enrolled [median age 9 years (range 3–19); 43% female]. As of December 15, 2019 median number of treatment cycle is 8 (range 1–24); 7 patients remain on treatment. Toxicity profile is similar to published reports with rash and elevated lipid profiles as most common adverse events. PFS6 for the entire cohort is 63%; PFS6 is 64% for the activated and 61% for the non-activated patients. Central imaging review (n=52) revealed 1 partial response, 1 complete response, 33 stable disease, and 17 progressive disease at the end of study treatment. Initial molecular analysis identified BRAF alterations in 35/65 patients.

CONCLUSION

Everolimus is well tolerated and active in a subset of pLGGs. Ongoing analyses will assess predictive biomarkers of response and will be reported at the meeting.

PATH-12. TEMOZOLOMIDE-INDUCED HYPERMUTATION IS ASSOCIATED WITH HIGH-GRADE TRANSFORMATION, DISTANT RECURRENCE AND REDUCED SURVIVAL IN INITIALLY LOW GRADE IDH-MUTANT GLIOMAS

Temozolomide, a commonly used alkylating agent, can induce somatic hypermutation in gliomas. The prevalence and implications of this phenomenon are not well characterized. Using targeted and whole exome sequencing from a cohort of 82 patients with recurrent IDH-mut LGG, we evaluated the clinical implications of hypermutation. Hypermutation was identified at transformation in 57% of recurrent gliomas exposed to TMZ and occurred for both IDH-mutant astrocytomas (52%) and oligodendrogliomas (64%). Among astrocytomas, receipt of radiotherapy prior to transformation was associated with decreased risk of hypermutation (11% vs 70%, p=0.0052), but this trend was not observed for oligodendrogliomas (78% vs 54%, p=NS). Among hypermutated tumors, 94% were transformed to higher WHO grades. Hypermutation was associated with transformation to higher WHO grade (OR 12.0 95% CI 2.5-115.5, p=0.002) and shorter survival after transformation (HR 2.1, 95% CI 1.1-4.0, p=0.018) compared with non-hypermutated transformed tumors. It remained prognostic (controlling for grade, molecular subtype, age, and prior radiotherapy. Patients with transformation to glioblastoma had poor survival regardless of hypermutation (p=0.78). Multivariate models were validated using an external, independent dataset (Harrel’s C=0.72). Strikingly, hypermutated tumors were also associated with development of discontiguous disease after transformation (3-year CI 41% vs 8% p=0.005), including ependymal and leptomeningeal distributions and four cases of spinal dissemination that were not observed in non-hypermutated tumors. These data have significant implications for management of IDH-mut LGG at recurrence.

CTNI-11. CC-115 IN NEWLY DIAGNOSED MGMT UNMETHYLATED GLIOBLASTOMA IN THE INDIVIDUALIZED SCREENING TRIAL OF INNOVATIVE GLIOBLASTOMA THERAPY (INSIGHT): A PHASE II RANDOMIZED BAYESIAN ADAPTIVE PLATFORM TRIAL

BACKGROUND

CC-115 is an oral, CNS-penetrant, selective inhibitor of mammalian target of rapamycin kinase (mTOR) and deoxyribonucleic acid-dependent protein kinase (DNA-PK). Both targets are important in glioblastoma; PI3K/Akt/mTOR signaling is hyperactive in most glioblastomas, and DNA-PK is integral to repair of radiotherapy-mediated DNA damage. To investigate CC-115 in newly diagnosed glioblastoma and explore potential genomic biomarker associations, CC-115 was evaluated in the Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) trial, an adaptive platform trial designed to efficiently test experimental agents.

METHODS

Adults with newly diagnosed MGMT-unmethylated glioblastoma, with genomic data available, are eligible for this ongoing trial. Patients are adaptively randomized to one of several experimental arms or the control arm: standard radiotherapy with concurrent and adjuvant temozolomide. The primary endpoint is overall survival (OS). Patients randomized to CC-115 (10mg po BID) received it concurrently with radiotherapy and as adjuvant monotherapy. As the first in-human use of CC-115 with radiation, a safety lead-in 3 + 3 design was used.

RESULTS

Twelve patients were randomized to CC-115; seven patients had possible treatment-related CTCAE grade &gt; 3 toxicity, including four pre-specified dose-limiting toxicities: liver function abnormality (n=1), hyperlipidemia (n=1), lipase elevation (n=1) and cerebral edema (n=1). There was no significant difference in progression-free survival (PFS, median 4.2 months [CC-115] vs. 5.2 months, p=0.9) or OS (median 10.1 months [CC-115] vs. 14.5 months, p=0.9) compared to the 50 patients randomized to the control arm. Based on early PFS results, randomization probability to CC-115 decreased from 25% to &lt; 10% at time of the trial arm closure.

CONCLUSION

Concurrent and adjuvant CC-115 was associated with toxicity and failed to improve PFS or OS. The INSIGhT trial design allowed for more efficient testing of CC-115, decreasing patients and resources allocated to a therapy that was discontinued due to concerns about toxicity and unfavorable risk-to-benefit ratio.

CTNI-12. PRELIMINARY RESULTS OF THE ABEMACICLIB ARM IN THE INDIVIDUALIZED SCREENING TRIAL OF INNOVATIVE GLIOBLASTOMA THERAPY (INSIGHT): A PHASE II PLATFORM TRIAL USING BAYESIAN ADAPTIVE RANDOMIZATION

BACKGROUND

The cyclin D-CDK4/6-Rb pathway is activated in most glioblastomas. Abemaciclib is a potent CDK4/6 inhibitor with good brain penetration approved for ER/PR/HER2- breast cancer. In order to efficiently evaluate the potential impact of abemaciclib on overall survival (OS) in newly diagnosed glioblastoma and to simultaneously develop information regarding potential genomic biomarker associations, abemaciclib was included as an arm on the Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) trial. INSIGhT is a phase II platform trial using response adaptive randomization and deep genomic profiling to more efficiently test experimental agents in MGMT unmethylated glioblastoma and potentially accelerate identification of novel therapies for phase III testing. Initial randomization was equal between abemaciclib, control, and two other experimental arms but subsequent randomization was adapted based on efficacy as determined by progression-free survival (PFS). Ineffective arms were discontinued and new arms added by protocol amendment. We report preliminary results for the abemaciclib arm which has completed accrual.

METHODS

Patients with newly diagnosed MGMT-unmethylated glioblastoma were randomized to receive either radiotherapy with concomitant and adjuvant temozolomide at standard doses or standard radiochemotherapy followed by adjuvant abemaciclib (150–200 mg orally BID) without temozolomide. Treatment continued until progression or development of unacceptable toxicities. The primary endpoint was OS. Association between abemaciclib efficacy and cyclin D-CDK4/6-Rb pathway genomic alterations was also investigated.

RESULTS

There were 123 patients (50 control; 73 treated with abemaciclib). Abemaciclib was generally well-tolerated with no new toxicity signals identified. PFS was significantly longer (p=0.03, logrank test) with abemaciclib (median 6.31 months 95% CI [5.29, 8.18]) compared to the control arm (5.16 months 95% CI [4.37, 6.28]). 28/50 control and 36/73 abemaciclib patients remain alive.

CONCLUSION

Preliminary analysis suggests that abemaciclib increases PFS compared to control. Updated toxicity, PFS and survival data and potential genomic biomarker associations will be presented.

Feasibility of hippocampal avoidance whole brain radiation in patients with hippocampal involvement: Data from a prospective study

PURPOSE

Among patients with brain metastases, hippocampal avoidance whole brain radiation (HA-WBRT) preserves neurocognitive function relative to conventional WBRT but the feasibility of hippocampal sparing in patients with metastases in/near the hippocampus is unknown. We identified the incidence of hippocampal/perihippocampal metastases and evaluated the feasibility of HA-WBRT in such patients.

MATERIALS/METHODS

Dosimetric data from 34 patients randomized to HA-WBRT (30 Gy/10 fractions) in a phase III trial (NCT03075072) comparing HA-WBRT to stereotactic radiation in patients with 5 to 20 brain metastases were analyzed. Patients with metastases in/near the hippocampi received HA-WBRT with prioritization of tumor coverage over hippocampal avoidance. Target coverage and hippocampal sparing metrics were compared between patients with targets in/near the hippocampus versus not.

RESULTS

In total, 9 of 34 (26%) patients had targets in the hippocampus and an additional 5 of 34 (15%) patients had targets in the hippocampal avoidance zone (HAZ, hippocampus plus 5 mm expansion) but outside the hippocampus. Patients with targets within the hippocampus and those with targets in the HAZ but outside the hippocampus were spared 34% and 73% of the ipsilateral mean biologically equivalent prescription dose, respectively. Of the latter cohort, 88% and 25% met conventional hippocampal sparing metrics of Dmin ≤ 9 Gy and Dmax ≤ 16 Gy, respectively. Among 11 patients with unilateral hippocampal/perihippocampal involvement, the uninvolved/contralateral hippocampus was limited to Dmin ≤ 9 Gy and Dmax ≤ 17 Gy in all cases.

CONCLUSIONS

In this study, a substantial percentage of patients with 5 to 20 brain metastases harbored metastases in/near the hippocampus. In such cases, minimizing hippocampal dose while providing tumor coverage was feasible and may translate to neurocognitive protection.

Clinical Impact of Tumor Mutational Burden in Neuroblastoma

BACKGROUND

Neuroblastoma is the most common pediatric extracranial solid tumor. Within conventional risk groups, there is considerable heterogeneity in outcomes, indicating the need for improved risk stratification.

METHODS

In this study we analyzed the somatic mutational burden of 515 primary, untreated neuroblastoma tumors from three independent cohorts. Mutations in coding regions were determined by whole-exome/genome sequencing of tumor samples compared to matched blood leukocytes. Survival data for 459 patients were available for analysis of 5-year overall survival using the Kaplan-Meier method and log-rank test. All statistical tests were two-sided.

RESULTS

Despite a low overall somatic mutational burden (mean = 3, range = 0-56), 107 patients were considered to have high mutational burden (>3 mutations). Unfavorable histology and age 18 months and older were associated with high mutational burden. Patients with high mutational burden had inferior 5-year overall survival (29.0%, 95% confidence interval [CI] = 17.2 to 41.8%) vs those with three or fewer somatic mutations (76.2%, 95% CI = 71.5 to 80.3%) (log-rank P < .001) and this association persisted when limiting the analysis to genes included on a 447-gene panel commonly used in clinical practice. On multivariable analysis, mutational burden remained prognostic independent of age, stage, histology and MYCN status.

CONCLUSIONS

This study demonstrates that mutational burden of primary neuroblastoma may be useful in combination with conventional risk factors to optimize risk stratification and guide treatment decisions, pending prospective validation.

Mechanisms and therapeutic implications of hypermutation in gliomas

A high tumour mutational burden (hypermutation) is observed in some gliomas1-5; however, the mechanisms by which hypermutation develops and whether it predicts the response to immunotherapy are poorly understood. Here we comprehensively analyse the molecular determinants of mutational burden and signatures in 10,294 gliomas. We delineate two main pathways to hypermutation: a de novo pathway associated with constitutional defects in DNA polymerase and mismatch repair (MMR) genes, and a more common post-treatment pathway, associated with acquired resistance driven by MMR defects in chemotherapy-sensitive gliomas that recur after treatment with the chemotherapy drug temozolomide. Experimentally, the mutational signature of post-treatment hypermutated gliomas was recapitulated by temozolomide-induced damage in cells with MMR deficiency. MMR-deficient gliomas were characterized by a lack of prominent T cell infiltrates, extensive intratumoral heterogeneity, poor patient survival and a low rate of response to PD-1 blockade. Moreover, although bulk analyses did not detect microsatellite instability in MMR-deficient gliomas, single-cell whole-genome sequencing analysis of post-treatment hypermutated glioma cells identified microsatellite mutations. These results show that chemotherapy can drive the acquisition of hypermutated populations without promoting a response to PD-1 blockade and supports the diagnostic use of mutational burden and signatures in cancer.

DRES-08. CLINICAL SIGNIFICANCE OF HYPERMUTATION IN GLIOMAS

BACKGROUND

Hypermutation is an emerging biomarker for predicting response to immunotherapy in cancer patients, however its clinical value in gliomas is not established. We sought to assess the determinants of hypermutation in gliomas, and its value for predicting response to standard of care and immune checkpoint blockade (ICB).

METHODS

We performed comprehensive genomic characterization of 2,420 clinically annotated gliomas. We assessed the clinical and molecular characteristics associated with hypermutation and relationships between hypermutation and response to cancer treatments.

RESULTS

Hypermutation occurred predominantly as an adaptive resistance mechanism to temozolomide in gliomas and was most prevalent in recurrent gliomas with MGMTpromoter methylation (33.8%), IDH1/2mutation (41.0%) or 1p/19q co-deletion (59.5%). Hypermutation was almost always associated with molecular defects in DNA mismatch repair (MMR), and was associated with shorter survival after its appearance based on multivariate analysis (hazard ratio 1.91; 95% CI 1.24–2.94; P=0.004). The molecular mechanisms whereby gliomas undergo hypermutation during therapy with alkylating agents were dissected using patient-derived glioma models in vitro and in vivo. Outcomes of hypermutated gliomas treated with immune checkpoint blockade or with standard of care agents will be presented at the conference.

CONCLUSIONS

Using the largest set of hypermutated gliomas described to date, this study establishes that mutational burden and mutation signatures are clinically and biologically significant biomarkers that can be used to predict therapy response and guide treatment decisions in gliomas

RBTT-09. A PHASE 1 STUDY OF CEMIPLIMAB IN PEDIATRIC PATIENTS WITH RELAPSED OR REFRACTORY (R/R) SOLID AND CENTRAL NERVOUS SYSTEM (CNS) TUMORS

DIPG and HGG lead to the majority of pediatric cancer-related deaths. Despite multimodal treatment, the 2-year survival rates for DIPG and HGG are less than 10% and 20%, respectively. Anti-PD-1 therapy combined with radiotherapy has demonstrated synergistic anti-tumor effects. Cemiplimab, a human PD-1 monoclonal antibody, has demonstrated safety and efficacy in patients with advanced malignancies. Combination of cemiplimab with radiation has the potential to be an effective treatment for pediatric patients with DIPG or HGG. This is a multicenter, Phase 1 and early efficacy study (NCT03690869). Phase 1 will enroll pediatric patients with R/R solid or CNS tumors (N≥30) into two age cohorts (0 to < 12 and 12 to < 18 years). Cemiplimab will be administered intravenously every 2 weeks as monotherapy. Primary objectives of Phase 1 are to confirm safety and assess the pharmacokinetics (PK) of cemiplimab to recommend a Phase 2 dose (RP2D) for clinical efficacy assessment. The Efficacy phase will enroll patients with newly diagnosed DIPG or HGG (dose escalation: N≥12 patients each; dose expansion: N≤40 patients each), or recurrent HGG (dose escalation: N≥6 patients; dose expansion: ≤20 patients) into two age cohorts (≥3 to < 12 years and 12 to ≤25 years). There will be two treatment arms for patients with newly diagnosed DIPG or HGG: cemiplimab in combination with conventionally fractionated (Arm 1) or hypofractionated (Arm 2) radiotherapy. Patients with recurrent HGG will receive cemiplimab concomitantly with reirradiation. All patients will continue cemiplimab as monotherapy at completion of combination therapy. Primary objectives of Efficacy Phase are to confirm safety and anticipated RP2D, assess PK, and determine survival and antitumor activity at 12 months (overall survival for newly diagnosed DIPG and recurrent HGG; progression-free survival for newly diagnosed HGG) of cemiplimab when given concomitantly with radiation. This study is currently recruiting patients across multiple sites.

PDTM-41. INHIBITION OF DNA DOUBLE STRAND BREAK REPAIR PATHWAYS AS A PROMISING THERAPEUTIC TARGET IN DIFFUSE INTRINSIC PONTINE GLIOMAS (DIPGs)

METHODS

To identify pathways critical for DIPG cell survival, genome wide CRISPR-Cas9 screen was performed on patient derived DIPG cell lines followed by gene set enrichment analyses. To monitor the effects of pathway inhibition on survival, apoptosis, DNA damage and repair, assays were performed to measure cell proliferation, cleaved-caspase3, gamma-H2AX and reporter based-DNA repair efficiency.

RESULTS

Our unbiased CRISPR approach to uncover vulnerabilities in DIPGs identified DNA double strand break (DSBs) repair pathways as essential for DIPG cell proliferation and survival. Further studies revealed high basal DSBs in DIPG cells compared to neural stem cells and primary astrocytes that suggest dependence of DIPG cell survival on specific DSB repair pathways. We confirmed the intrinsic reliance of DIPG cells on the specific DSB repair pathway of mutagenic end-joining, and defined a key role for DNA repair in suppressing endogenous DNA damage-induced apoptotic cell death.

CONCLUSION

DIPG cells have high endogenous DNA damage levels and escape catastrophic genomic instability and cell death by engaging DNA repair pathways, in particular the mutagenic end-joining DNA repair pathway. Inhibition of this specific DNA repair pathway represents a promising new avenue for the treatment of DIPGs.

ACTR-42. PI3K/mTOR PATHWAY ACTIVATION SELECTED PHASE II STUDY OF EVEROLIMUS (RAD001) WITH AND WITHOUT TEMOZOLOMIDE IN THE TREATMENT OF ADULT PATIENTS WITH SUPRATENTORIAL LOW-GRADE GLIOMA [NCT NCT02023905]

Functional activation of the PI3K/AKT/mTOR pathway is seen in ~50% of low-grade gliomas and correlates with worse survival. Everolimus is a selective inhibitor of mTOR that targets mTOR-raptor signaling, halting proliferation and indirectly inhibiting angiogenesis. This phase 2 study evaluated the efficacy of everolimus in untreated grade II diffuse glioma. Patients were stratified by 1p19q status and PI3K pathway activation (via phosphorylation of PRAS-40) into three arms: 1) 1p19q intact, PRAS-40 phosphorylated received everolimus monotherapy; 2) 1p19q intact, PRAS-40 not phosphorylated received everolimus with temozolomide; and 3) 1p19q co-deleted received everolimus monotherapy. Primary outcome was landmark PFS-33 months for Arms 1 and 2; and PFS-38 months for Arm 3 (null hypothesis 50% for all arms individually). Key eligibility criteria included central pathology confirmation, no prior treatment, and initiation of everolimus within 120 days of most recent tissue sampling. From 05/2014 to 07/2018, 27 patients were enrolled – 16 into Arm 1; 2 into Arm 2; and 9 into Arm 3. Median age at enrollment was 38 years (range 21 – 65); median KPS 90 (range 70 – 100) and a majority were male (74%). Although follow-up is not complete, as of 05/2019 11 of 16 patients had progressed prior to 33 months in Arm 1, and 5 of 9 patients had progressed prior to 38 months in Arm 3. Toxicity was as expected with frequent grade 1/2 AEs of diarrhea, rash, and mucositis. Headache was the most common grade 3 AE and was seen in three cases. The study was closed prematurely secondary to slow accrual and loss of drug support. Updated survival data as well as results of secondary and exploratory analyses will be reported. In summary, everolimus was well tolerated in previously untreated low-grade gliomas. However, it failed to meet primary outcome of extending PFS in this population.