Clinical outcomes of patients with CIC-rearranged sarcoma: a single institution retrospective analysis.

PURPOSE: CIC-rearranged sarcomas represent a type of undifferentiated small round cell sarcoma (USRCS) characterized by poor survival, rapid development of chemotherapy resistance, and high rates of metastasis. We aim to contribute to the growing body of knowledge regarding diagnosis, treatment, clinical course, and outcomes for these patients. METHODS: This case series investigates the clinical courses of ten patients with CIC-rearranged sarcoma treated at the Johns Hopkins Hospital from July 2014 through January 2024. Clinical data were retrospectively extracted from electronic medical records. RESULTS: Patients ranged from 10 to 67 years of age at diagnosis, with seven patients presenting with localized disease and three with metastatic disease. Tumors originated from soft tissues of various anatomic locations. Mean overall survival (OS) was 22.1 months (10.6-52.2), and mean progression-free survival (PFS) was 16.7 months (5.3-52.2). Seven patients received intensive systemic therapy with an Ewing sarcoma-directed regimen or a soft tissue sarcoma-directed regimen. Three patients experienced prolonged disease-free survival without systemic treatment. CONCLUSION: Most patients in this case series demonstrated aggressive clinical courses consistent with those previously described in the literature, although we note a spectrum of clinical outcomes not previously reported. The diversity of clinical courses underscores the need for an improved understanding of individual tumor biology to enhance clinical decision-making and patient prognosis. Despite its limitations, this article broadens the spectrum of reported clinical outcomes, providing a valuable addition to the published literature on this rare cancer.

Early detection of malignant and pre-malignant peripheral nerve tumors using cell-free DNA fragmentomics.

Early detection of neurofibromatosis type 1 (NF1) associated peripheral nerve sheath tumors (PNST) informs clinical decision-making, potentially averting deadly outcomes. Here, we describe a cell-free DNA (cfDNA) fragmentomic approach which distinguishes non-malignant, pre-malignant and malignant forms of NF1 PNST. Using plasma samples from a novel cohort of 101 NF1 patients and 21 healthy controls, we validated that our previous cfDNA copy number alteration (CNA)-based approach identifies malignant peripheral nerve sheath tumor (MPNST) but cannot distinguish among benign and premalignant states. We therefore investigated the ability of fragment-based cfDNA features to differentiate NF1-associated tumors including binned genome-wide fragment length ratios, end motif analysis, and non-negative matrix factorization deconvolution of fragment lengths. Fragmentomic methods were able to differentiate pre-malignant states including atypical neurofibromas (AN). Fragmentomics also adjudicated AN cases suspicious for MPNST, correctly diagnosing samples noninvasively, which could have informed clinical management. Overall, this study pioneers the early detection of malignant and premalignant peripheral nerve sheath tumors in NF1 patients using plasma cfDNA fragmentomics. In addition to screening applications, this novel approach distinguishes atypical neurofibromas from benign plexiform neurofibromas and malignant peripheral nerve sheath tumors, enabling more precise clinical diagnosis and management.

Impact of Consolidative Radiation on Overall and Progression-Free Survival in Pediatric, Adolescent, and Young Adult Metastatic Bone and Soft Tissue Sarcoma.

PURPOSE: To determine the association between consolidative radiation (RT) and survival in children, adolescents, and young adults with metastatic sarcoma. METHODS AND MATERIALS: Eligibility criteria included patients aged ≤39 years with newly diagnosed metastatic bone or soft tissue sarcoma who completed local control of the primary tumor without disease progression. Consolidative RT was defined as RT to all known sites of metastatic disease. The Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). The least absolute shrinkage and selection operator Cox provided adjusted estimates. To account for immortal time bias, consolidative RT was used as a time-varying covariate in a time dependent Cox model. Distant failure was estimated using the Fine-Gray model. RESULTS: Patients (n = 85) had a median age at diagnosis of 14.8 years. Most common histology was Ewing Sarcoma (45.9%) followed by rhabdomyosarcoma (40.0%). Receipt of consolidative RT was associated with Ewing Sarcoma (P < .001) and local control modality as those who underwent local control with surgery and RT compared with surgery alone were more likely to be treated with consolidative RT (P = .034). Consolidative RT was independently associated with improved OS (hazard ratio [HR], 0.41; 95% CI, 0.17-0.98; P = .045) and improved PFS (HR, 0.37; 95% CI, 0.16-0.88; P = .024) after adjusting for confounding variables and immortal time bias. Patients treated with consolidative RT also experienced a lower risk of distant failure (HR, 0.33; 95% CI, 0.17-0.64; P = .001). In an independent data set of patients with metachronous progression (n = 36), consolidative RT remained independently associated with improved OS. CONCLUSIONS: Consolidative RT was independently associated with improved OS and PFS and decreased risk of distant failure in child, adolescent, and young adult patients with metastatic sarcoma. Future work should evaluate biomarkers to optimize patient selection, timing, and dose for consolidative RT.

Spatial Gene-Expression Profiling Unveils Immuno-oncogenic Programs of NF1-Associated Peripheral Nerve Sheath Tumor Progression.

PURPOSE: Plexiform neurofibromas (PNF) are benign peripheral nerve sheath tumors (PNST) associated with neurofibromatosis type 1 (NF1). Despite similar histologic appearance, these neoplasms exhibit diverse evolutionary trajectories, with a subset progressing to malignant peripheral nerve sheath tumor (MPNST), the leading cause of premature death in individuals with NF1. Malignant transformation of PNF often occurs through the development of atypical neurofibroma (ANF) precursor lesions characterized by distinct histopathologic features and CDKN2A copy-number loss. Although genomic studies have uncovered key driver events promoting tumor progression, the transcriptional changes preceding malignant transformation remain poorly defined. EXPERIMENTAL DESIGN: Here we resolve gene-expression profiles in PNST across the neurofibroma-to-MPNST continuum in NF1 patients and mouse models, revealing early molecular features associated with neurofibroma evolution and transformation. RESULTS: Our findings demonstrate that ANF exhibit enhanced signatures of antigen presentation and immune response, which are suppressed as malignant transformation ensues. MPNST further displayed deregulated survival and mitotic fidelity pathways, and targeting key mediators of these pathways, CENPF and BIRC5, disrupted the growth and viability of human MPNST cell lines and primary murine Nf1-Cdkn2a-mutant Schwann cell precursors. Finally, neurofibromas contiguous with MPNST manifested distinct alterations in core oncogenic and immune surveillance programs, suggesting that early molecular events driving disease progression may precede histopathologic evidence of malignancy. CONCLUSIONS: If validated prospectively in future studies, these signatures may serve as molecular diagnostic tools to augment conventional histopathologic diagnosis by identifying neurofibromas at high risk of undergoing malignant transformation, facilitating risk-adapted care.

Analysis of treatment sequence and outcomes in patients with relapsed malignant peripheral nerve sheath tumors.

Background: Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas originating from cellular components within the nerve sheath. The incidence of MPNST is highest in people with neurofibromatosis type 1 (NF1), and MPNST is the leading cause of death for these individuals. Complete surgical resection is the only curative therapeutic option, but is often unfeasible due to tumor location, size, or presence of metastases. Evidence-based choices of chemotherapy for recurrent/refractory MPNST remain elusive. To address this gap, we conducted a retrospective analysis of our institutional experience in treating patients with relapsed MPNST in order to describe patient outcomes related to salvage regimens. Methods: We conducted a retrospective electronic health record analysis of patients with MPNST who were treated at Johns Hopkins Hospital from January 2010 to June 2021. We calculated time to progression (TTP) based on salvage chemotherapy regimens. Results: Sixty-five patients were included in the analysis. Upfront therapy included single or combined modalities of surgery, chemotherapy, or radiotherapy. Forty-eight patients received at least 1 line of chemotherapy, which included 23 different regimens (excluding active clinical studies). Most patients (n = 42, 87.5%) received a combination of doxorubicin, ifosfamide, or etoposide as first-line chemotherapy. Salvage chemotherapy regimens and their TTP varied greatly, with irinotecan/temozolomide-based regimens having the longest average TTP (255.5 days, among 4 patients). Conclusions: Patients with advanced or metastatic MPNST often succumb to their disease despite multiple lines of therapy. These data may be used as comparative information in decision-making for future patients and clinical trials.

CDK4/6 inhibition enhances SHP2 inhibitor efficacy and is dependent upon RB function in malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas with limited treatment options, and new effective therapeutic strategies are desperately needed. We observe antiproliferative potency of genetic depletion of PTPN11 or pharmacological inhibition using the SHP2 inhibitor (SHP2i) TNO155. Our studies into the signaling response to SHP2i reveal that resistance to TNO155 is partially mediated by reduced RB function, and we therefore test the addition of a CDK4/6 inhibitor (CDK4/6i) to enhance RB activity and improve TNO155 efficacy. In combination, TNO155 attenuates the adaptive response to CDK4/6i, potentiates its antiproliferative effects, and converges on enhancement of RB activity, with greater suppression of cell cycle and inhibitor-of-apoptosis proteins, leading to deeper and more durable antitumor activity in in vitro and in vivo patient-derived models of MPNST, relative to either single agent. Overall, our study provides timely evidence to support the clinical advancement of this combination strategy in patients with MPNST and other tumors driven by loss of NF1.

Pro-905, a Novel Purine Antimetabolite, Combines with Glutamine Amidotransferase Inhibition to Suppress Growth of Malignant Peripheral Nerve Sheath Tumor.

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive soft-tissue sarcomas that arise from neural tissues and carry a poor prognosis. Previously, we found that the glutamine amidotransferase inhibitor JHU395 partially impeded tumor growth in preclinical models of MPNST. JHU395 inhibits de novo purine synthesis in human MPNST cells and murine tumors with partial decreases in purine monophosphates. On the basis of prior studies showing enhanced efficacy when glutamine amidotransferase inhibition was combined with the antimetabolite 6-mercaptopurine (6-MP), we hypothesized that such a combination would be efficacious in MPNST. Given the known toxicity associated with 6-MP, we set out to develop a more efficient and well-tolerated drug that targets the purine salvage pathway. Here, we report the discovery of Pro-905, a phosphoramidate protide that delivered the active nucleotide antimetabolite thioguanosine monophosphate (TGMP) to tumors over 2.5 times better than equimolar 6-MP. Pro-905 effectively prevented the incorporation of purine salvage substrates into nucleic acids and inhibited colony formation of human MPNST cells in a dose-dependent manner. In addition, Pro-905 inhibited MPNST growth and was well-tolerated in both human patient-derived xenograft (PDX) and murine flank MPNST models. When combined with JHU395, Pro-905 enhanced the colony formation inhibitory potency of JHU395 in human MPNST cells and augmented the antitumor efficacy of JHU395 in mice. In summary, the dual inhibition of the de novo and purine salvage pathways in preclinical models may safely be used to enhance therapeutic efficacy against MPNST.

Adolescent and Young Adult (AYA) Oncology, Version 2.2024, NCCN Clinical Practice Guidelines in Oncology.

This selection from the NCCN Guidelines for Adolescent and Young Adult (AYA) Oncology focuses on considerations for the comprehensive care of AYA patients with cancer. Compared with older adults with cancer, AYA patients have unique needs regarding treatment, fertility counseling, psychosocial and behavioral issues, and supportive care services. The complete version of the NCCN Guidelines for Adolescent and Young Adult (AYA) Oncology addresses additional aspects of caring for AYA patients, including risk factors, screening, diagnosis, and survivorship.

CDK4/6-MEK Inhibition in MPNSTs Causes Plasma Cell Infiltration, Sensitization to PD-L1 Blockade, and Tumor Regression.

PURPOSE: Malignant peripheral nerve sheath tumors (MPNST) are lethal, Ras-driven sarcomas that lack effective therapies. We investigated effects of targeting cyclin-dependent kinases 4 and 6 (CDK4/6), MEK, and/or programmed death-ligand 1 (PD-L1) in preclinical MPNST models. EXPERIMENTAL DESIGN: Patient-matched MPNSTs and precursor lesions were examined by FISH, RNA sequencing, IHC, and Connectivity-Map analyses. Antitumor activity of CDK4/6 and MEK inhibitors was measured in MPNST cell lines, patient-derived xenografts (PDX), and de novo mouse MPNSTs, with the latter used to determine anti-PD-L1 response. RESULTS: Patient tumor analyses identified CDK4/6 and MEK as actionable targets for MPNST therapy. Low-dose combinations of CDK4/6 and MEK inhibitors synergistically reactivated the retinoblastoma (RB1) tumor suppressor, induced cell death, and decreased clonogenic survival of MPNST cells. In immune-deficient mice, dual CDK4/6-MEK inhibition slowed tumor growth in 4 of 5 MPNST PDXs. In immunocompetent mice, combination therapy of de novo MPNSTs caused tumor regression, delayed resistant tumor outgrowth, and improved survival relative to monotherapies. Drug-sensitive tumors that regressed contained plasma cells and increased cytotoxic T cells, whereas drug-resistant tumors adopted an immunosuppressive microenvironment with elevated MHC II-low macrophages and increased tumor cell PD-L1 expression. Excitingly, CDK4/6-MEK inhibition sensitized MPNSTs to anti-PD-L1 immune checkpoint blockade (ICB) with some mice showing complete tumor regression. CONCLUSIONS: CDK4/6-MEK inhibition induces a novel plasma cell-associated immune response and extended antitumor activity in MPNSTs, which dramatically enhances anti-PD-L1 therapy. These preclinical findings provide strong rationale for clinical translation of CDK4/6-MEK-ICB targeted therapies in MPNST as they may yield sustained antitumor responses and improved patient outcomes.

Complex/cryptic EWSR1::FLI1/ERG Gene Fusions and 1q Jumping Translocation in Pediatric Ewing Sarcomas.

Ewing sarcomas (ES) are rare small round cell sarcomas often affecting children and characterized by gene fusions involving one member of the FET family of genes (usually EWSR1) and a member of the ETS family of transcription factors (usually FLI1 or ERG). The detection of EWSR1 rearrangements has important diagnostic value. Here, we conducted a retrospective review of 218 consecutive pediatric ES at diagnosis and found eight patients having data from chromosome analysis, FISH/microarray, and gene-fusion assay. Three of these eight ES had novel complex/cryptic EWSR1 rearrangements/fusions by chromosome analysis. One case had a t(9;11;22)(q22;q24;q12) three-way translocation involving EWSR1::FLI1 fusion and 1q jumping translocation. Two cases had cryptic EWSR1 rearrangements/fusions, including one case with a cryptic t(4;11;22)(q35;q24;q12) three-way translocation involving EWSR1::FLI1 fusion, and the other had a cryptic EWSR1::ERG rearrangement/fusion on an abnormal chromosome 22. All patients in this study had various aneuploidies with a gain of chromosome 8 (75%), the most common, followed by a gain of chromosomes 20 (50%) and 4 (37.5%), respectively. Recognition of complex and/or cryptic EWSR1 gene rearrangements/fusions and other chromosome abnormalities (such as jumping translocation and aneuploidies) using a combination of various genetic methods is important for accurate diagnosis, prognosis, and treatment outcomes of pediatric ES.

Ex vivo to in vivo model of malignant peripheral nerve sheath tumors for precision oncology.

BACKGROUND: Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas that often develop in patients with neurofibromatosis type 1 (NF1). To address the critical need for novel therapeutics in MPNST, we aimed to establish an ex vivo 3D platform that accurately captured the genomic diversity of MPNST and could be utilized in a medium-throughput manner for drug screening studies to be validated in vivo using patient-derived xenografts (PDX). METHODS: Genomic analysis was performed on all PDX-tumor pairs. Selected PDX were harvested for assembly into 3D microtissues. Based on prior work in our labs, we evaluated drugs (trabectedin, olaparib, and mirdametinib) ex vivo and in vivo. For 3D microtissue studies, cell viability was the endpoint as assessed by Zeiss Axio Observer. For PDX drug studies, tumor volume was measured twice weekly. Bulk RNA sequencing was performed to identify pathways enriched in cells. RESULTS: We developed 13 NF1-associated MPNST-PDX and identified mutations or structural abnormalities in NF1 (100%), SUZ12 (85%), EED (15%), TP53 (15%), CDKN2A (85%), and chromosome 8 gain (77%). We successfully assembled PDX into 3D microtissues, categorized as robust (>90% viability at 48 h), good (>50%), or unusable (<50%). We evaluated drug response to "robust" or "good" microtissues, namely MN-2, JH-2-002, JH-2-079-c, and WU-225. Drug response ex vivo predicted drug response in vivo, and enhanced drug effects were observed in select models. CONCLUSIONS: These data support the successful establishment of a novel 3D platform for drug discovery and MPNST biology exploration in a system representative of the human condition.

MEK Inhibition Synergizes with TYK2 Inhibitors in NF1-Associated Malignant Peripheral Nerve Sheath Tumors.

PURPOSE: Malignant peripheral nerve sheath tumors (MPNST) are aggressive sarcomas with limited treatment options and poor survival rates. About half of MPNST cases are associated with the neurofibromatosis type 1 (NF1) cancer predisposition syndrome. Overexpression of TYK2 occurs in the majority of MPNST, implicating TYK2 as a therapeutic target. EXPERIMENTAL DESIGN: The effects of pharmacologic TYK2 inhibition on MPNST cell proliferation and survival were examined using IncuCyte live cell assays in vitro, and downstream actions were analyzed using RNA-sequencing (RNA-seq), qPCR arrays, and validation of protein changes with the WES automated Western system. Inhibition of TYK2 alone and in combination with MEK inhibition was evaluated in vivo using both murine and human MPNST cell lines, as well as MPNST PDX. RESULTS: Pharmacologic inhibition of TYK2 dose-dependently decreased proliferation and induced apoptosis over time. RNA-seq pathway analysis on TYK2 inhibitor-treated MPNST demonstrated decreased expression of cell cycle, mitotic, and glycolysis pathways. TYK2 inhibition resulted in upregulation of the MEK/ERK pathway gene expression, by both RNA-seq and qPCR array, as well as increased pERK1/2 levels by the WES Western system. The compensatory response was tested with dual treatment with TYK2 and MEK inhibitors, which synergistically decreased proliferation and increased apoptosis in vitro. Finally, combination therapy was shown to inhibit growth of MPNST in multiple in vivo models. CONCLUSIONS: These data provide the preclinical rationale for the development of a phase I clinical trial of deucravacitinib and mirdametinib in NF1-assosciated MPNST.

Diffuse Pulmonary Metastases at Presentation of Giant Cell Tumor of Bone: A Case Report and Synthesis of Literature.

CASE: We present a 23-year-old man with acute-on-chronic shoulder pain with an aggressive-appearing, destructive lesion of the left proximal humerus and diffuse lung metastases. Biopsy revealed conventional giant cell tumor of bone (GCTB) without sarcomatous differentiation, treated with resection and proximal humerus reconstruction. Without systemic treatment, his pulmonary metastases demonstrated modest spontaneous regression, with no impairment of pulmonary function. CONCLUSIONS: Although GCTB is known to metastasize to lungs, these deposits most commonly follow local recurrence. We describe a young adult with diffuse pulmonary nodules at initial presentation, although still following an indolent clinical course without the need for additional systemic therapy.

CDK4/6 inhibition enhances SHP2 inhibitor efficacy and is dependent upon restoration of RB function in malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive soft tissue sarcomas with limited treatment options, and novel effective therapeutic strategies are desperately needed. We observe anti-proliferative efficacy of genetic depletion or pharmacological inhibition using the clinically available SHP2 inhibitor (SHP2i) TNO155. Our studies into the signaling response to SHP2i reveal that resistance to TNO155 is partially mediated by reduced RB function, and we therefore test the addition of a CDK4/6 inhibitor (CDK4/6i) to enhance RB activity and improve TNO155 efficacy. In combination, TNO155 attenuates the adaptive response to CDK4/6i, potentiates its anti-proliferative effects, and converges on enhancement of RB activity, with greater suppression of cell cycle and inhibitor-of-apoptosis proteins, leading to deeper and more durable anti-tumor activity in in vitro and in vivo patient-derived models of MPNST, relative to either single agent. Overall, our study provides timely evidence to support the clinical advancement of this combination strategy in patients with MPNST and other tumors driven by loss of NF1.

Integrated molecular and clinical analysis of BRAF-mutant glioma in adults.

BRAF mutations are a significant driver of disease in pediatric low-grade glioma, but the implications of BRAF alterations on the clinical course and treatment response in adult glioma remain unclear. Here, we characterize a multi-institutional cohort of more than 300 patients (>200 adults) with BRAF-mutated glioma using clinical, pathological/molecular, and outcome data. We observed that adult and pediatric BRAF-mutant gliomas harbor distinct clinical and molecular features, with a higher prevalence of BRAFV600E (Class I) and BRAF fusions in pediatric tumors. BRAFV600E alterations were associated with improved survival in adults with glioma overall, though not in glioblastoma. Other genomic alterations observed within functional classes were consistent with the putative roles of those BRAF mutation classes in glioma pathogenesis. In our adult cohort, BRAFV600E alterations conferred sensitivity to targeted therapies. Overall, this large cohort of BRAF-altered adult gliomas demonstrates a broad range of molecular alterations with implications for treatment sensitivity and survival.

Unresectable Metastatic Testicular Germ Cell Tumor With Low-grade Neuroglial Neoplasm, Stable After Radiation and Chemotherapy.

We present an 18-year-old male patient who presented with a 16 cm testicular tumor alongside multiple lesions in the lungs, right pelvis with involvement of the ischio/pubic bone, and enlarged pelvic lymph nodes on imaging, suspicious for metastatic disease. Histologic and immunohistochemical examinations revealed an embryonic type neuroectodermal tumor (somatic-type malignancy, 10%) arising in a malignant mixed germ cell tumor composed of teratoma (50%), embryonal carcinoma (10%) and yolk sac tumor (30%). After treatment with chemotherapy and radiation, repeat imaging demonstrated a right pelvic sidewall mass that decreased in size from 40 mm at 11 months after the initial diagnosis to 18 mm at 22 months after the initial diagnosis. A right pelvis medial thigh wall mass that had a lytic bone component showed a slight increase in size from 151 mm at 11 months after the initial diagnosis to 154 mm at 22 months after the diagnosis. On biopsies performed at 3, 10, and 26 months after the initial diagnosis, this lytic lesion consistently demonstrated a neoplasm composed of low-grade neuroglial differentiation. This is the first case in the medical literature where a residual malignant germ cell tumor consisting of low-grade neuroglial neoplasm is in a site that is not amenable to resection without significant morbidity. The tumor initially regressed with the traditional first-line chemo-radiotherapy regimen but regrew and stabilized with a second regimen of chemotherapy. The clinical course of this case invites consideration for an active surveillance approach in cases with similar characteristics.

Single-cell multiomics identifies clinically relevant mesenchymal stem-like cells and key regulators for MPNST malignancy.

Malignant peripheral nerve sheath tumor (MPNST), a highly aggressive Schwann cell (SC)-derived soft tissue sarcoma, arises from benign neurofibroma (NF); however, the identity, heterogeneity and origins of tumor populations remain elusive. Nestin+ cells have been implicated as tumor stem cells in MPNST; unexpectedly, single-cell profiling of human NF and MPNST and their animal models reveal a broad range of nestin-expressing SC lineage cells and dynamic acquisition of discrete cancer states during malignant transformation. We uncover a nestin-negative mesenchymal neural crest-like subpopulation as a previously unknown malignant stem-like state common to murine and human MPNSTs, which correlates with clinical severity. Integrative multiomics profiling further identifies unique regulatory networks and druggable targets against the malignant subpopulations in MPNST. Targeting key epithelial-mesenchymal transition and stemness regulators including ZEB1 and ALDH1A1 impedes MPNST growth. Together, our studies reveal the underlying principles of tumor cell-state evolution and their regulatory circuitries during NF-to-MPNST transformation, highlighting a hitherto unrecognized mesenchymal stem-like subpopulation in MPNST disease progression.

Therapeutic Vulnerability to ATR Inhibition in Concurrent NF1 and ATRX-Deficient/ALT-Positive High-Grade Solid Tumors.

Subsets of Neurofibromatosis Type 1 (NF1)-associated solid tumors have been shown to display high frequencies of ATRX mutations and the presence of alternative lengthening of telomeres (ALT). We studied the phenotype of combined NF1 and ATRX deficiency in malignant solid tumors. Cell lines derived from NF1-deficient sporadic glioblastomas (U251, SF188), an NF1-associated ATRX mutant glioblastoma cell line (JHH-NF1-GBM1), an NF1-derived sarcoma cell line (JHH-CRC65), and two NF1-deficient MPNST cell lines (ST88-14, NF90.8) were utilized. Cancer cells were treated with ATR inhibitors, with or without a MEK inhibitor or temozolomide. In contrast to the glioma cell line SF188, combined ATRX knockout (KO) and TERC KO led to ALT-like properties and sensitized U251 glioma cells to ATR inhibition in vitro and in vivo. In addition, ATR inhibitors sensitized U251 cells to temozolomide, but not MEK inhibition, irrespective of ATRX level manipulation; whereas, the JHH-NF1-GBM1 cell line demonstrated sensitivity to ATR inhibition, but not temozolomide. Similar effects were noted using the MPNST cell line NF90.8 after combined ATRX knockdown and TERC KO; however, not in ST88-14. Taken together, our study supports the feasibility of targeting the ATR pathway in subsets of NF1-deficient and associated tumors.