Auto-segmentation of neck nodal metastases using self-distilled masked image transformer on longitudinal MR images.

Objectives: Auto-segmentation promises greater speed and lower inter-reader variability than manual segmentations in radiation oncology clinical practice. This study aims to implement and evaluate the accuracy of the auto-segmentation algorithm, "Masked Image modeling using the vision Transformers (SMIT)," for neck nodal metastases on longitudinal T2-weighted (T2w) MR images in oropharyngeal squamous cell carcinoma (OPSCC) patients. Methods: This prospective clinical trial study included 123 human papillomaviruses (HPV-positive [+]) related OSPCC patients who received concurrent chemoradiotherapy. T2w MR images were acquired on 3 T at pre-treatment (Tx), week 0, and intra-Tx weeks (1-3). Manual delineations of metastatic neck nodes from 123 OPSCC patients were used for the SMIT auto-segmentation, and total tumor volumes were calculated. Standard statistical analyses compared contour volumes from SMIT vs manual segmentation (Wilcoxon signed-rank test [WSRT]), and Spearman's rank correlation coefficients (ρ) were computed. Segmentation accuracy was evaluated on the test data set using the dice similarity coefficient (DSC) metric value. P-values <0.05 were considered significant. Results: No significant difference in manual and SMIT delineated tumor volume at pre-Tx (8.68 ± 7.15 vs 8.38 ± 7.01 cm3, P = 0.26 [WSRT]), and the Bland-Altman method established the limits of agreement as -1.71 to 2.31 cm3, with a mean difference of 0.30 cm3. SMIT model and manually delineated tumor volume estimates were highly correlated (ρ = 0.84-0.96, P < 0.001). The mean DSC metric values were 0.86, 0.85, 0.77, and 0.79 at the pre-Tx and intra-Tx weeks (1-3), respectively. Conclusions: The SMIT algorithm provides sufficient segmentation accuracy for oncological applications in HPV+ OPSCC. Advances in knowledge: First evaluation of auto-segmentation with SMIT using longitudinal T2w MRI in HPV+ OPSCC.

Hypoxia-Directed Treatment of Human Papillomavirus-Related Oropharyngeal Carcinoma.

PURPOSE: Standard curative-intent chemoradiotherapy for human papillomavirus (HPV)-related oropharyngeal carcinoma results in significant toxicity. Since hypoxic tumors are radioresistant, we posited that the aerobic state of a tumor could identify patients eligible for de-escalation of chemoradiotherapy while maintaining treatment efficacy. METHODS: We enrolled patients with HPV-related oropharyngeal carcinoma to receive de-escalated definitive chemoradiotherapy in a phase II study (ClinicalTrials.gov identifier: NCT03323463). Patients first underwent surgical removal of disease at their primary site, but not of gross disease in the neck. A baseline 18F-fluoromisonidazole positron emission tomography scan was used to measure tumor hypoxia and was repeated 1-2 weeks intratreatment. Patients with nonhypoxic tumors received 30 Gy (3 weeks) with chemotherapy, whereas those with hypoxic tumors received standard chemoradiotherapy to 70 Gy (7 weeks). The primary objective was achieving a 2-year locoregional control (LRC) of 95% with a 7% noninferiority margin. RESULTS: One hundred fifty-eight patients with T0-2/N1-N2c were enrolled, of which 152 patients were eligible for analyses. Of these, 128 patients met criteria for 30 Gy and 24 patients received 70 Gy. The 2-year LRC was 94.7% (95% CI, 89.8 to 97.7), meeting our primary objective. With a median follow-up time of 38.3 (range, 22.1-58.4) months, the 2-year progression-free survival (PFS) and overall survival (OS) rates were 94% and 100%, respectively, for the 30-Gy cohort. The 70-Gy cohort had similar 2-year PFS and OS rates at 96% and 96%, respectively. Acute grade 3-4 adverse events were more common in 70 Gy versus 30 Gy (58.3% v 32%; P = .02). Late grade 3-4 adverse events only occurred in the 70-Gy cohort, in which 4.5% complained of late dysphagia. CONCLUSION: Tumor hypoxia is a promising approach to direct dosing of curative-intent chemoradiotherapy for HPV-related carcinomas with preserved efficacy and substantially reduced toxicity that requires further investigation.

Predicting response to immune checkpoint blockade therapy among mismatch repair-deficient patients using mutational signatures.

Despite the overall efficacy of immune checkpoint blockade (ICB) for mismatch repair deficiency (MMRD) across tumor types, a sizable fraction of patients with MMRD still do not respond to ICB. We performed mutational signature analysis of panel sequencing data (n = 95) from MMRD cases treated with ICB. We discover that T>C-rich single base substitution (SBS) signatures-SBS26 and SBS54 from the COSMIC Mutational Signatures catalog-identify MMRD patients with significantly shorter overall survival. Tumors with a high burden of SBS26 show over-expression and enriched mutations of genes involved in double-strand break repair and other DNA repair pathways. They also display chromosomal instability (CIN), likely related to replication fork instability, leading to copy number losses that trigger immune evasion. SBS54 is associated with transcriptional activity and not with CIN, defining a distinct subtype. Consistently, cancer cell lines with a high burden of SBS26 and SBS54 are sensitive to treatments targeting pathways related to their proposed etiology. Together, our analysis offers an explanation for the heterogeneous responses to ICB among MMRD patients and supports an SBS signature-based predictor as a prognostic biomarker for differential ICB response.

Mining cancer genomes for change-of-metabolic-function mutations.

Enzymes with novel functions are needed to enable new organic synthesis techniques. Drawing inspiration from gain-of-function cancer mutations that functionally alter proteins and affect cellular metabolism, we developed METIS (Mutated Enzymes from Tumors In silico Screen). METIS identifies metabolism-altering cancer mutations using mutation recurrence rates and protein structure. We used METIS to screen 298,517 cancer mutations and identify 48 candidate mutations, including those previously identified to alter enzymatic function. Unbiased metabolomic profiling of cells exogenously expressing a candidate mutant (OGDHLp.A400T) supports an altered phenotype that boosts in vitro production of xanthosine, a pharmacologically useful chemical that is currently produced using unsustainable, water-intensive methods. We then applied METIS to 49 million cancer mutations, yielding a refined set of candidates that may impart novel enzymatic functions or contribute to tumor progression. Thus, METIS can be used to identify and catalog potentially-useful cancer mutations for green chemistry and therapeutic applications.

Clinical Importance of Clonal Hematopoiesis in Metastatic Gastrointestinal Tract Cancers.

Importance: Clonal hematopoiesis (CH) has been associated with development of atherosclerosis and leukemia and worse survival among patients with cancer; however, the association with cancer therapy efficacy, in particular immune checkpoint blockade (ICB), and toxicity has not yet been established. Given the widespread use of ICB and the critical role hematopoietic stem cell-derived lymphocytes play in mediating antitumor responses, CH may be associated with therapeutic efficacy and hematologic toxicity. Objective: To determine the association between CH and outcomes, hematologic toxicity, and therapeutic efficacy in patients with metastatic gastrointestinal tract cancers being treated with systemic therapy, both in the first-line metastatic treatment setting and in ICB. Design, Setting, and Participants: This retrospective cohort study included 633 patients with stage IV colorectal (CRC) and esophagogastric (EGC) cancer who were treated with first-line chemotherapy and/or ICB at Memorial Sloan Kettering Cancer Center. Patients underwent matched tumor and peripheral blood DNA sequencing using the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets next-generation sequencing assay between January 1, 2006, and December 31, 2020. Exposures: Clonal hematopoiesis-related genetic alterations were identified by next-generation sequencing of patients' tumor and normal blood buffy coat samples, with a subset of these CH alterations annotated as likely putative drivers (CH-PD) based upon previously established criteria. Main Outcomes and Measures: Patients with CH and CH-PD in peripheral blood samples were identified, and these findings were correlated with survival outcomes (progression-free survival [PFS] and overall survival [OS]) during first-line chemotherapy and ICB, as well as baseline white blood cell levels and the need for granulocyte colony-stimulating factor (G-CSF) support. Results: Among the 633 patients included in the study (390 men [61.6%]; median age, 58 [IQR, 48-66] years), the median age was 52 (IQR, 45-63) years in the CRC group and 61 (IQR, 53-69) years in the EGC group. In the CRC group, 161 of 301 patients (53.5%) were men, compared with 229 of 332 patients (69.0%) in the EGC group. Overall, 62 patients (9.8%) were Asian, 45 (7.1%) were Black or African American, 482 (76.1%) were White, and 44 (7.0%) were of unknown race or ethnicity. Presence of CH was identified in 115 patients with EGC (34.6%) and 83 with CRC (27.6%), with approximately half of these patients harboring CH-PD (CRC group, 44 of 83 [53.0%]; EGC group, 55 of 115 [47.8%]). Patients with EGC and CH-PD exhibited a significantly worse median OS of 16.0 (95% CI, 11.6-22.3) months compared with 21.6 (95% CI, 19.6-24.3) months for those without CH-PD (P = .01). For patients with CRC and EGC, CH and CH-PD were not associated with PFS differences in patients undergoing ICB or first-line chemotherapy. Neither CH nor CH-PD were correlated with baseline leukocyte levels or increased need for G-CSF support. Conclusions and Relevance: These findings suggest CH and CH-PD are not directly associated with the treatment course of patients with metastatic gastrointestinal tract cancer receiving cancer-directed therapy.

(R)-2-Hydroxyglutarate Inhibits KDM5 Histone Lysine Demethylases to Drive Transformation in IDH-Mutant Cancers.

Oncogenic mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 occur in a wide range of cancers, including acute myeloid leukemia (AML) and glioma. Mutant IDH enzymes convert 2-oxoglutarate (2OG) to (R)-2-hydroxyglutarate [(R)-2HG], an oncometabolite that is hypothesized to promote cellular transformation by dysregulating 2OG-dependent enzymes. The only (R)-2HG target that has been convincingly shown to contribute to transformation by mutant IDH is the myeloid tumor suppressor TET2. However, there is ample evidence to suggest that (R)-2HG has other functionally relevant targets in IDH-mutant cancers. Here, we show that (R)-2HG inhibits KDM5 histone lysine demethylases and that this inhibition contributes to cellular transformation in IDH-mutant AML and IDH-mutant glioma. These studies provide the first evidence of a functional link between dysregulation of histone lysine methylation and transformation in IDH-mutant cancers. SIGNIFICANCE: Mutant IDH is known to induce histone hypermethylation. However, it is not known if this hypermethylation is functionally significant or is a bystander effect of (R)-2HG accumulation in IDH-mutant cells. Here, we provide evidence that KDM5 inhibition by (R)-2HG contributes to mutant IDH-mediated transformation in AML and glioma. This article is highlighted in the In This Issue feature, p. 1275.

Cancer-associated SMARCAL1 loss-of-function mutations promote alternative lengthening of telomeres and tumorigenesis in telomerase-negative glioblastoma cells.

BACKGROUND: Telomere maintenance mechanisms are required to enable the replicative immortality of malignant cells. While most cancers activate the enzyme telomerase, a subset of cancers uses telomerase-independent mechanisms termed alternative lengthening of telomeres (ALT). ALT occurs via homology-directed-repair mechanisms and is frequently associated with ATRX mutations. We previously showed that a subset of adult glioblastoma (GBM) patients with ATRX-expressing ALT-positive tumors harbored loss-of-function mutations in the SMARCAL1 gene, which encodes an annealing helicase involved in replication fork remodeling and the resolution of replication stress. However, the causative relationship between SMARCAL1 deficiency, tumorigenesis, and de novo telomere synthesis is not understood. METHODS: We used a patient-derived ALT-positive GBM cell line with native SMARCAL1 deficiency to investigate the role of SMARCAL1 in ALT-mediated de novo telomere synthesis, replication stress, and gliomagenesis in vivo. RESULTS: Inducible rescue of SMARCAL1 expression suppresses ALT indicators and inhibits de novo telomere synthesis in GBM and osteosarcoma cells, suggesting that SMARCAL1 deficiency plays a functional role in ALT induction in cancers that natively lack SMARCAL1 function. SMARCAL1-deficient ALT-positive cells can be serially propagated in vivo in the absence of detectable telomerase activity, demonstrating that the SMARCAL1-deficient ALT phenotype maintains telomeres in a manner that promotes tumorigenesis. CONCLUSIONS: SMARCAL1 deficiency is permissive to ALT and promotes gliomagenesis. Inducible rescue of SMARCAL1 in ALT-positive cell lines permits the dynamic modulation of ALT activity, which will be valuable for future studies aimed at understanding the mechanisms of ALT and identifying novel anticancer therapeutics that target the ALT phenotype.

PD-1 Blockade in Solid Tumors with Defects in Polymerase Epsilon.

Missense mutations in the polymerase epsilon (POLE) gene have been reported to generate proofreading defects resulting in an ultramutated genome and to sensitize tumors to checkpoint blockade immunotherapy. However, many POLE-mutated tumors do not respond to such treatment. To better understand the link between POLE mutation variants and response to immunotherapy, we prospectively assessed the efficacy of nivolumab in a multicenter clinical trial in patients bearing advanced mismatch repair-proficient POLE-mutated solid tumors. We found that only tumors harboring selective POLE pathogenic mutations in the DNA binding or catalytic site of the exonuclease domain presented high mutational burden with a specific single-base substitution signature, high T-cell infiltrates, and a high response rate to anti-PD-1 monotherapy. This study illustrates how specific DNA repair defects sensitize to immunotherapy. POLE proofreading deficiency represents a novel agnostic biomarker for response to PD-1 checkpoint blockade therapy. SIGNIFICANCE: POLE proofreading deficiency leads to high tumor mutational burden with high tumor-infiltrating lymphocytes and predicts anti-PD-1 efficacy in mismatch repair-proficient tumors. Conversely, tumors harboring POLE mutations not affecting proofreading derived no benefit from PD-1 blockade. POLE proofreading deficiency is a new tissue-agnostic biomarker for cancer immunotherapy. This article is highlighted in the In This Issue feature, p. 1397.

The Role of Ablative Radiotherapy in Older Adults With Limited Metastatic Disease.

For patients with oligometastatic cancer, radiotherapy presents a promising avenue for achieving meaningful symptom relief and durable disease control. Data from recently published and ongoing randomized studies are helping to define the appropriate contexts for effective intervention with stereotactic ablative body radiotherapy (SABR) in the oligometastatic setting. Importantly, older adults represent a significant portion of patients with oligometastatic disease, yet often comprise a minority of patients in clinical trials. Moreover, older adults of the same chronologic age may have variable degrees of fitness and frailty. In this review, we highlight the specific challenges and considerations for the use of radiotherapy for older adults with oligometastatic disease-noting the importance of geriatric assessments in clinical decision-making about the appropriateness of SABR and other metastasis-directed therapies in this population. We then review data from existing trials, including a subset analysis of adverse events and survival estimates among older adults enrolled in the landmark SABR-COMET trial. Finally, we discuss future directions for research, including the need for focused clinical trials in older adult cohorts. Ultimately, a multidisciplinary approach is critical when carefully balancing the potential risks and benefits of this emerging treatment paradigm in the older adult population.

Dual role of allele-specific DNA hypermethylation within the TERT promoter in cancer.

Aberrant activation of telomerase in human cancer is achieved by various alterations within the TERT promoter, including cancer-specific DNA hypermethylation of the TERT hypermethylated oncological region (THOR). However, the impact of allele-specific DNA methylation within the TERT promoter on gene transcription remains incompletely understood. Using allele-specific next-generation sequencing, we screened a large cohort of normal and tumor tissues (n = 652) from 10 cancer types and identified that differential allelic methylation (DAM) of THOR is restricted to cancerous tissue and commonly observed in major cancer types. THOR-DAM was more common in adult cancers, which develop through multiple stages over time, than in childhood brain tumors. Furthermore, THOR-DAM was especially enriched in tumors harboring the activating TERT promoter mutations (TPMs). Functional studies revealed that allele-specific gene expression of TERT requires hypomethylation of the core promoter, both in TPM and TERT WT cancers. However, the expressing allele with hypomethylated core TERT promoter universally exhibits hypermethylation of THOR, while the nonexpressing alleles are either hypermethylated or hypomethylated throughout the promoter. Together, our findings suggest a dual role for allele-specific DNA methylation within the TERT promoter in the regulation of TERT expression in cancer.

TP53 wild-type/PPM1D mutant diffuse intrinsic pontine gliomas are sensitive to a MDM2 antagonist.

Diffuse intrinsic pontine gliomas (DIPGs) are high-grade tumors of the brainstem that often occur in children, with a median overall survival of less than one year. Given the fact that DIPGs are resistant to chemotherapy and are not amenable to surgical resection, it is imperative to develop new therapeutic strategies for this deadly disease. The p53 pathway is dysregulated by TP53 (~ 60%) or PPM1D gain-of-function mutations (~ 30%) in DIPG cases. PPM1D gain-of-function mutations suppress p53 activity and result in DIPG tumorigenesis. While MDM2 is a major negative regulator of p53, the efficacy of MDM2 inhibitor has not been tested in DIPG preclinical models. In this study, we performed a comprehensive validation of MDM2 inhibitor RG7388 in patient-derived DIPG cell lines established from both TP53 wild-type/PPM1D-mutant and TP53 mutant/PPM1D wild-type tumors, as well in TP53 knockout isogenic DIPG cell line models. RG7388 selectively inhibited the proliferation of the TP53 wild-type/PPM1D mutant DIPG cell lines in a dose- and time-dependent manner. The anti-proliferative effects were p53-dependent. RNA-Seq data showed that differential gene expression induced by RG7388 treatment was enriched in the p53 pathways. RG7388 reactivated the p53 pathway and induced apoptosis as well as G1 arrest. In vivo, RG7388 was able to reach the brainstem and exerted therapeutic efficacy in an orthotopic DIPG xenograft model. Hence, this study demonstrates the pre-clinical efficacy potential of RG7388 in the TP53 wild-type/PPM1D mutant DIPG subgroup and may provide critical insight on the design of future clinical trials applying this drug in DIPG patients.

SMARCAL1 loss and alternative lengthening of telomeres (ALT) are enriched in giant cell glioblastoma.

Subsets of high-grade gliomas, including glioblastoma (GBM), are known to utilize the alternative lengthening of telomeres (ALT) pathway for telomere length maintenance. However, the telomere maintenance profile of one subtype of GBM-giant cell GBM-has not been extensively studied. Here, we investigated the prevalence of ALT, as well as ATRX and SMARCAL1 protein loss, in a cohort of classic giant cell GBM and GBM with giant cell features. To determine the presence of ALT, a telomere-specific fluorescence in situ hybridization assay was performed on 15 cases of classic giant cell GBM, 28 additional GBMs found to have giant cell features, and 1 anaplastic astrocytoma with giant cell features. ATRX, SMARCAL1, and IDH1 protein status were assessed in a proportion of cases by immunohistochemistry and were compared to clinical-pathologic and molecular characteristics. In the overall cohort of 44 cases, 19 (43%) showed evidence of ALT. Intriguingly, of the ALT-positive cases, only 9 (47.4%) displayed loss of the ALT suppressor ATRX by immunohistochemistry. Since inactivating mutations in SMARCAL1 have been identified in ATRX wild-type ALT-positive gliomas, we developed an immunohistochemistry assay for SMARCAL1 protein expression using genetically validated controls. Of the 19 ALT-positive cases, 6 (31.5%) showed loss or mis-localization of SMARCAL1 by immunohistochemistry. Of these cases, four retained ATRX protein expression, while two cases also displayed ATRX loss. Additionally, we assessed five cases from which multiple temporal samples were available and ALT status was concordant between both tumor biopsies. In summary, we have identified a subset of giant cell GBM that utilize the ALT telomere maintenance mechanism. Importantly, in addition to ATRX loss, ALT-positive tumors harboring SMARCAL1 alterations are prevalent in giant cell GBM.

The integrated genomic and epigenomic landscape of brainstem glioma.

Brainstem gliomas are a heterogeneous group of tumors that encompass both benign tumors cured with surgical resection and highly lethal cancers with no efficacious therapies. We perform a comprehensive study incorporating epigenetic and genomic analyses on a large cohort of brainstem gliomas, including Diffuse Intrinsic Pontine Gliomas. Here we report, from DNA methylation data, distinct clusters termed H3-Pons, H3-Medulla, IDH, and PA-like, each associated with unique genomic and clinical profiles. The majority of tumors within H3-Pons and-H3-Medulla harbors H3F3A mutations but shows distinct methylation patterns that correlate with anatomical localization within the pons or medulla, respectively. Clinical data show significantly different overall survival between these clusters, and pathway analysis demonstrates different oncogenic mechanisms in these samples. Our findings indicate that the integration of genetic and epigenetic data can facilitate better understanding of brainstem gliomagenesis and classification, and guide future studies for the development of novel treatments for this disease.

Targeting Mutant PPM1D Sensitizes Diffuse Intrinsic Pontine Glioma Cells to the PARP Inhibitor Olaparib.

Diffuse intrinsic pontine glioma (DIPG) is an invariably fatal brain tumor occurring predominantly in children. Up to 90% of pediatric DIPGs harbor a somatic heterozygous mutation resulting in the replacement of lysine 27 with methionine (K27M) in genes encoding histone H3.3 (H3F3A, 65%) or H3.1 (HIST1H3B, 25%). Several studies have also identified recurrent truncating mutations in the gene encoding protein phosphatase 1D, PPM1D, in 9%-23% of DIPGs. Here, we sought to investigate the therapeutic potential of targeting PPM1D, alone or in combination with inhibitors targeting specific components of DNA damage response pathways in patient-derived DIPG cell lines. We found that GSK2830371, an allosteric PPM1D inhibitor, suppressed the proliferation of PPM1D-mutant, but not PPM1D wild-type DIPG cells. We further observed that PPM1D inhibition sensitized PPM1D-mutant DIPG cells to PARP inhibitor (PARPi) treatment. Mechanistically, combined PPM1D and PARP inhibition show synergistic effects on suppressing a p53-dependent RAD51 expression and the formation of RAD51 nuclear foci, possibly leading to impaired homologous recombination (HR)-mediated DNA repair in PPM1D-mutant DIPG cells. Collectively, our findings reveal the potential role of the PPM1D-p53 signaling axis in the regulation of HR-mediated DNA repair and provide preclinical evidence demonstrating that combined inhibition of PPM1D and PARP1/2 may be a promising therapeutic combination for targeting PPM1D-mutant DIPG tumors. IMPLICATIONS: The findings support the use of PARPi in combination with PPM1D inhibition against PPM1D-mutant DIPGs.

Genome-Wide CRISPR-Cas9 Screen Reveals Selective Vulnerability of ATRX-Mutant Cancers to WEE1 Inhibition.

The tumor suppressor gene ATRX is frequently mutated in a variety of tumors including gliomas and liver cancers, which are highly unresponsive to current therapies. Here, we performed a genome-wide synthetic lethal screen, using CRISPR-Cas9 genome editing, to identify potential therapeutic targets specific for ATRX-mutated cancers. In isogenic hepatocellular carcinoma (HCC) cell lines engineered for ATRX loss, we identified 58 genes, including the checkpoint kinase WEE1, uniquely required for the cell growth of ATRX null cells. Treatment with the WEE1 inhibitor AZD1775 robustly inhibited the growth of several ATRX-deficient HCC cell lines in vitro, as well as xenografts in vivo. The increased sensitivity to the WEE1 inhibitor was caused by accumulated DNA damage-induced apoptosis. AZD1775 also selectively inhibited the proliferation of patient-derived primary cell lines from gliomas with naturally occurring ATRX mutations, indicating that the synthetic lethal relationship between WEE1 and ATRX could be exploited in a broader spectrum of human tumors. As WEE1 inhibitors have been investigated in several phase II clinical trials, our discovery provides the basis for an easily clinically testable therapeutic strategy specific for cancers deficient in ATRX. SIGNIFICANCE: ATRX-mutant cancer cells depend on WEE1, which provides a basis for therapeutically targeting WEE1 in ATRX-deficient cancers.See related commentary by Cole, p. 375.

CRISPR Editing of Mutant IDH1 R132H Induces a CpG Methylation-Low State in Patient-Derived Glioma Models of G-CIMP.

Mutations in isocitrate dehydrogenases 1 and 2 (IDH) occur in the majority of World Health Organization grade II and III gliomas. IDH1/2 active site mutations confer a neomorphic enzyme activity producing the oncometabolite D-2-hydroxyglutarate (D-2HG), which generates the glioma CpG island methylation phenotype (G-CIMP). While IDH1/2 mutations and G-CIMP are commonly retained during tumor recurrence, recent work has uncovered losses of the IDH1 mutation in a subset of secondary glioblastomas. Cooccurrence of the loss of the mutant allele with extensive methylation changes suggests a possible link between the two phenomena. Here, we utilize patient-derived IDH1R132H/WT glioma cell lines and CRISPR-Cas9-mediated gene knockout to model the genetic loss of IDH1 R132H, and characterize the effects of this deletion on DNA methylation. After D-2HG production has been abolished by deletions within the IDH1 alleles, these models show persistent DNA hypermethylation at seven CpG sites previously used to define G-CIMP-positivity in patient tumor samples. Despite these defining G-CIMP sites showing persistent hypermethylation, we observed a genome-wide pattern of DNA demethylation, enriched for CpG sites located within open sea regions of the genome, as well as in CpG-island shores of transcription start sites, after loss of D-2HG production. These results suggest that inhibition of D-2HG from genetic deletion of IDH alleles is not sufficient to reverse hypermethylation of all G-CIMP-defining CpG sites, but does result in more demethylation globally and may contribute to the formation of a G-CIMP-low-like phenotype. IMPLICATIONS: These findings show that loss of the IDH1 mutation in malignant glioma cells leads to a pattern of DNA methylation alterations, and shows plausibility of IDH1 mutation loss being causally related to the gain of a G-CIMP-low-like phenotype.

Detection of early-stage hepatocellular carcinoma in asymptomatic HBsAg-seropositive individuals by liquid biopsy.

Liquid biopsies, based on cell free DNA (cfDNA) and proteins, have shown the potential to detect early stage cancers of diverse tissue types. However, most of these studies were retrospective, using individuals previously diagnosed with cancer as cases and healthy individuals as controls. Here, we developed a liquid biopsy assay, named the hepatocellular carcinoma screen (HCCscreen), to identify HCC from the surface antigen of hepatitis B virus (HBsAg) positive asymptomatic individuals in the community population. The training cohort consisted of individuals who had liver nodules and/or elevated serum α-fetoprotein (AFP) levels, and the assay robustly separated those with HCC from those who were non-HCC with a sensitivity of 85% and a specificity of 93%. We further applied this assay to 331 individuals with normal liver ultrasonography and serum AFP levels. A total of 24 positive cases were identified, and a clinical follow-up for 6-8 mo confirmed four had developed HCC. No HCC cases were diagnosed from the 307 test-negative individuals in the follow-up during the same timescale. Thus, the assay showed 100% sensitivity, 94% specificity, and 17% positive predictive value in the validation cohort. Notably, each of the four HCC cases was at the early stage (<3 cm) when diagnosed. Our study provides evidence that the use of combined detection of cfDNA alterations and protein markers is a feasible approach to identify early stage HCC from asymptomatic community populations with unknown HCC status.

Molecular profiling of tumors of the brainstem by sequencing of CSF-derived circulating tumor DNA.

Brainstem gliomas are molecularly heterogeneous diseases, many of which are difficult to safely surgically resect and have limited treatment options due to their eloquent location. These constraints pose challenges to biopsy, which limits the use of routine molecular profiling and identification of personalized therapies. Here, we explored the potential of sequencing of circulating tumor DNA (ctDNA) isolated from the cerebrospinal fluid (CSF) of brainstem glioma patients as a less invasive approach for tumor molecular profiling. CSF was obtained from patients either intraoperatively (91.2%, 52/57), from ventricular-peritoneal shunt (3.5%, 2/57), or by lumbar puncture (5.3%, 3/57), all prior to surgical manipulation of the tumor. Deep sequencing of glioma-associated genes was performed on CSF-derived ctDNA and, where available, matched blood and tumor DNA from 57 patients, including nine medullary and 23 diffuse intrinsic pontine gliomas (DIPG). At least one tumor-specific mutation was detected in over 82.5% of CSF ctDNA samples (47/57). In cases with primary tumors harboring at least one mutation, alterations were identified in the CSF ctDNA of 97.3% of cases (36/37). In over 83% (31/37) of cases, all primary tumor alterations were detected in the CSF, and in 91.9% (34/37) of cases, at least half of the alterations were identified. Among ten patients found to have primary tumors negative for mutations, 30% (3/10) had detectable somatic alterations in the CSF. Finally, mutation detection using plasma ctDNA was less sensitive than sequencing the CSF ctDNA (38% vs. 100%, respectively). Our study indicates that deep sequencing of CSF ctDNA is a reliable technique for detecting tumor-specific alterations in brainstem tumors. This approach may offer an alternative approach to stereotactic biopsy for molecular profiling of brainstem tumors.

Sensitive and rapid detection of TERT promoter and IDH mutations in diffuse gliomas.

BACKGROUND: Mutations in telomerase reverse transcriptase promoter (TERTp) and isocitrate dehydrogenase 1 and 2 (IDH) offer objective markers to assist in classifying diffuse gliomas into genetic subgroups. However, traditional mutation detection techniques lack sensitivity or have long turnaround times or high costs. We developed GliomaDx, an allele-specific, locked nucleic acid-based quantitative PCR assay to overcome these limitations and sensitively detect TERTp and IDH mutations. METHODS: We evaluated the performance of GliomaDx on cell line DNA and frozen tissue diffuse glioma samples with variable tumor percentage to mimic use in clinical settings and validated low percentage variants using sensitive techniques including droplet digital PCR (ddPCR) and next-generation sequencing. We also developed GliomaDx Nest, which incorporates a high-fidelity multiplex pre-amplification step prior to allele-specific PCR for low-input formalin-fixed paraffin embedded (FFPE) samples. RESULTS: GliomaDx detects the TERTp and IDH1 alterations at an analytical sensitivity of 0.1% mutant allele fraction, corresponding to 0.2% tumor cellularity. GliomaDx identified TERTp/IDH1 alterations in a cohort of frozen tissue samples with variable tumor percentage of all major diffuse glioma histologic types. GliomaDx Nest is able to detect these hotspot mutations with similar sensitivity from pre-amplified samples and was successfully tested on a cohort of clinical FFPE samples. Testing of a cohort of previously identified TERTpWT-IDHWT gliomas (by Sanger sequencing) revealed that 26.3% harbored low-percentage mutations. Analysis by ddPCR and whole exome sequencing of these tumors confirmed the low mutant fraction of these alterations and overall mutation-based tumor purity. CONCLUSIONS: Our results show that GliomaDx can rapidly detect TERTp/IDH mutations with high sensitivity, identifying cases that might be missed due to the lack of sensitivity of other techniques. This approach may facilitate more objective classification of diffuse glioma samples in clinical settings such as intraoperative diagnosis or in testing cases with low tumor purity.