Detection of tumor-derived cell-free DNA in cerebrospinal fluid using a clinically validated targeted sequencing panel for pediatric brain tumors.

PURPOSE: Clinical sequencing of tumor DNA is necessary to render an integrated diagnosis and select therapy for children with primary central nervous system (CNS) tumors, but neurosurgical biopsy is not without risk. In this study, we describe cell-free DNA (cfDNA) in blood and cerebrospinal fluid (CSF) as sources for "liquid biopsy" in pediatric brain tumors. METHODS: CSF samples were collected by lumbar puncture, ventriculostomy, or surgery from pediatric patients with CNS tumors. Following extraction, CSF-derived cfDNA was sequenced using UW-OncoPlex™, a clinically validated next-generation sequencing platform. CSF-derived cfDNA results and paired plasma and tumor samples concordance was also evaluated. RESULTS: Seventeen CSF samples were obtained from 15 pediatric patients with primary CNS tumors. Tumor types included medulloblastoma (n = 7), atypical teratoid/rhabdoid tumor (n = 2), diffuse midline glioma with H3 K27 alteration (n = 4), pilocytic astrocytoma (n = 1), and pleomorphic xanthoastrocytoma (n = 1). CSF-derived cfDNA was detected in 9/17 (53%) of samples, and sufficient for sequencing in 8/10 (80%) of extracted samples. All somatic mutations and copy-number variants were also detected in matched tumor tissue, and tumor-derived cfDNA was absent in plasma samples and controls. Tumor-derived cfDNA alterations were detected in the absence of cytological evidence of malignant cells in as little as 200 µl of CSF. Several clinically relevant alterations, including a KIAA1549::BRAF fusion were detected. CONCLUSIONS: Clinically relevant genomic alterations are detectable using CSF-derived cfDNA across a range of pediatric brain tumors. Next-generation sequencing platforms are capable of producing a high yield of DNA alterations with 100% concordance rate with tissue analysis.

Looking beyond year 1 in the molecular era of pediatric brain tumor diagnosis: confirmatory testing of germline variants found on tumor sequencing.

Purpose: Somatic molecular profiling of pediatric brain tumors aids with the diagnosis and treatment of patients with a variety of high- and low-grade central nervous system neoplasms. Here, we report follow-up targeted germline evaluation for patients with possible germline variants following tumor only testing in the initial year in which somatic molecular testing was implemented at a single institution. Patients and Methods: Somatic testing was completed for all tumors of the central nervous system (CNS) undergoing diagnostic workup at Seattle Children's Hospital during the study period of November 2015 to November 2016. Sequencing was performed in a College of American Pathologists-accredited, Clinical Laboratory Improvements Amendments-certified laboratory using UW-OncoPlex™ assay (version 5), a DNA-based targeted next generation sequencing panel validated to detect genetic alterations in 262 cancer-related genes. We tracked subsequent clinical evaluation and testing on a subgroup of this cohort found to have potential germline variants of interest. Results: Molecular sequencing of 88 patients' tumors identified 31 patients with variants that warranted consideration of germline testing. To date, 19 (61%) patients have been tested. Testing confirmed germline variants for ten patients (31% of those identified for testing), one with two germline variants (NF1 and mosaic TP53). Eight (26%) patients died before germline testing was sent. One patient (13%) has not yet had testing. Conclusion: Clinically validated molecular profiling of pediatric brain tumors identifies patients who warrant further germline evaluation. Despite this, only a subset of these patients underwent the indicated confirmatory sequencing. Further work is needed to identify barriers and facilitators to this testing, including the role of genetic counseling and consideration of upfront paired somatic-germline testing.

Diffuse hemispheric glioma with H3 p.K28M (K27M) mutation: Unusual non-midline presentation of diffuse midline glioma, H3 K27M-altered?

Diffuse midline glioma, H3 K27-altered (DMG-H3 K27) is an aggressive group of diffuse gliomas that predominantly occurs in pediatric patients, involves midline structures, and displays loss of H3 p.K28me3 (K27me3) expression by immunohistochemistry and characteristic genetic/epigenetic profile. Rare examples of a diffuse glioma with an H3 p.K28M (K27M) mutation and without involvement of the midline structures, so-called "diffuse hemispheric glioma with H3 p.K28M (K27M) mutation" (DHG-H3 K27), have been reported. Herein, we describe 2 additional cases of radiologically confirmed DHG-H3 K27 and summarize previously reported cases. We performed histological, immunohistochemical, molecular, and DNA methylation analysis and provided clinical follow-up in both cases. Overall, DHG-H3 K27 is an unusual group of diffuse gliomas that shows similar clinical, histopathological, genomic, and epigenetic features to DMG-H3 K27 as well as enrichment for activating alterations in MAPK pathway genes. These findings suggest that DHG-H3 K27 is closely related to DMG-H3 K27 and may represent an unusual presentation of DMG-H3 K27 without apparent midline involvement and with frequent MAPK pathway activation. Detailed reports of additional cases with clinical follow-up will be important to expand our understanding of this unusual group of diffuse gliomas and to better define the clinical outcome and how to classify DHG-H3 K27.

Somatic Versus Germline: A Case Series of Three Children With ATM-Mutated Medulloblastoma.

Somatic versus Germline-A Case Series of Three Children with ATM- mutated Medulloblastoma.

Current clinical practices and challenges in molecular testing: a GOAL Consortium Hematopathology Working Group report.

While molecular testing of hematologic malignancies is now standard of care, there is variability in practice and testing capabilities between different academic laboratories, with common questions arising on how to best meet clinical expectations. A survey was sent to hematopathology subgroup members of the Genomics Organization for Academic Laboratories consortium to assess current and future practice and potentially establish a reference for peer institutions. Responses were received from 18 academic tertiary-care laboratories regarding next-generation sequencing (NGS) panel design, sequencing protocols and metrics, assay characteristics, laboratory operations, case reimbursement, and development plans. Differences in NGS panel size, use, and gene content were reported. Gene content for myeloid processes was reported to be generally excellent, while genes for lymphoid processes were less well covered. The turnaround time (TAT) for acute cases, including acute myeloid leukemia, was reported to range from 2 to 7 calendar days to 15 to 21 calendar days, with different approaches to achieving rapid TAT described. To help guide NGS panel design and standardize gene content, consensus gene lists based on current and future NGS panels in development were generated. Most survey respondents expected molecular testing at academic laboratories to continue to be viable in the future, with rapid TAT for acute cases likely to remain an important factor. Molecular testing reimbursement was reported to be a major concern. The results of this survey and subsequent discussions improve the shared understanding of differences in testing practices for hematologic malignancies between institutions and will help provide a more consistent level of patient care.

Diagnosis of Ovarian Carcinoma Homologous Recombination DNA Repair Deficiency From Targeted Gene Capture Oncology Assays.

PURPOSE: Homologous recombination DNA repair deficiency (HRD) is a therapeutic biomarker for sensitivity to platinum and poly(ADP-ribose) polymerase inhibitor therapies in breast and ovarian cancers. Several molecular phenotypes and diagnostic strategies have been developed to assess HRD; however, their clinical implementation remains both technically challenging and methodologically unstandardized. METHODS: We developed and validated an efficient and cost-effective strategy for HRD determination on the basis of calculation of a genome-wide loss of heterozygosity (LOH) score through targeted, hybridization capture and next-generation DNA sequencing augmented with 3,000 common, polymorphic single-nucleotide polymorphism (SNP) sites distributed genome-wide. This approach requires minimal sequence reads and can be readily integrated into targeted gene capture workflows already in use for molecular oncology. We interrogated 99 ovarian neoplasm-normal pairs using this method and compared results with patient mutational genotypes and orthologous predictors of HRD derived from whole-genome mutational signatures. RESULTS: LOH scores of ≥11% had >86% sensitivity for identifying tumors with HRD-causing mutations in an independent validation set (90.6% sensitivity for all specimens). We found strong agreement of our analytic approach with genome-wide mutational signature assays for determining HRD, yielding an estimated 96.7% sensitivity and 50% specificity. We observed poor concordance with mutational signatures inferred using only mutations detected by the targeted gene capture panel, suggesting inadequacy of the latter approach. LOH score did not significantly correlate with treatment outcomes. CONCLUSION: Targeted sequencing of genome-wide polymorphic SNP sites can be used to infer LOH events and subsequently diagnose HRD in ovarian tumors. The methods presented here are readily generalizable to other targeted gene oncology assays and could be adapted for HRD diagnosis in other tumor types.

Bilateral Ovarian Sertoli-Leydig Cell Tumors Harboring DICER1 Germline and Distinct Somatic Mutations: Case Report and Literature Review.

Background: DICER1 tumor predisposition syndrome is characterized by an increased risk for development of pleuropulmonary blastoma, pituitary blastoma, multinodular thyroid goiter, thyroid carcinoma, sex cord stromal tumor, cystic nephroma, embryonal rhabdomyosarcoma, and tumors of the CNS, amongst others. Of this list, only pituitary blastoma is recognized as pathognomonic for the syndrome. Case report: We describe a 15-year-old female with bilateral, asynchronous Sertoli-Leydig cell tumors (SLCT). Both tumors harbored an identical germline frameshift mutation as well as unique somatic DICER1 hot-spot point mutations. Discussion: A review of bilateral SLCTs demonstrates that all patients with available DICER1 mutation status carried a germline DICER1 mutation (100%, 9 of 9). In cases with known somatic DICER1 status on bilateral tumors, all harbored distinct somatic mutations (100%, 5 of 5). Our findings support the notion that bilateral ovarian SLCTs are indeed separate events and do not represent recurrent or metastatic disease.

When Tissue Is the Issue: Expanding Cell-Free DNA "Liquid Biopsies" to Supernatants and Nonplasma Biofluids.

While tissue biopsy remains the gold standard for tumor biomarker testing, assays using plasma-derived cfDNA, aka circulating-tumor DNA (ctDNA), have recently demonstrated validity in the setting of limited tissue or recurrent disease. Tumor-derived cfDNA is also present in nonplasma biofluids and supernatants procured through interventional procedures. Evaluation of cfDNA extracted from these fluids may have benefits at nearly every stage of cancer patient management, from diagnosis and prognosis to monitoring disease progression and predicting therapeutic response. This review will focus on preanalytical, analytical, and postanalytical variables that must be considered when analyzing "liquid biopsies" outside the plasma compartment.

Isolated MLH1 Loss by Immunohistochemistry Because of Benign Germline MLH1 Polymorphisms.

PURPOSE: Mismatch repair (MMR) immunohistochemistry (IHC) is frequently used to inform prognosis, select (immuno-)therapy, and identify patients for heritable cancer syndrome testing. However, false-negative and false-positive MMR IHC interpretations have been described. MATERIALS AND METHODS: Following identification of discordant MMR IHC and DNA-based microsatellite instability testing in a patient with colorectal carcinoma, we retrospectively reviewed institutional archives to identify patient samples with similar discrepancies. RESULTS: We report a patient with metastatic colorectal carcinoma who initially received immunotherapy on the basis of apparent isolated loss of MLH1 by IHC; notably, MLH1 promoter hypermethylation was negative. Subsequent evaluation of neoplastic tissue on a DNA-based targeted next-generation sequencing panel demonstrated microsatellite stability, low tumor mutational burden, and a benign MLH1 variant, MLH1 p.V384D, accompanied by loss of heterozygosity. The constellation of findings and repeat MLH1 IHC demonstrating retained expression using a different antibody-clone, supported reclassification of the neoplasm as MMR-proficient. Immunotherapy was discontinued, and cytotoxic chemotherapy was initiated. This index case of apparent discordance between MMR IHC and DNA-based microsatellite instability prompted a retrospective review of institutional archives to identify patient samples with similar discrepancies. Further evaluation of neoplasms harboring MLH1 p.V384D with loss of heterozygosity revealed systematic antibody-dependent interference. The review also identified a second IHC-interference candidate, MLH1 p.A441T. CONCLUSION: This study confirms that rare germline polymorphisms can result in incorrect IHC results, potentially affecting selection of optimal therapy and the decision to pursue germline testing. This case further highlights the need for expert molecular pathologic review and communication between clinical and molecular oncology teams.

Congenital Infantile Fibrosarcoma Involving Pelvic Wall and Thigh Soft Tissues and Placenta, Presenting with Coagulopathy.

Infantile fibrosarcoma (IF) is a well characterized pediatric malignancy marked by gene rearrangements involving members of the NTRK family. In this report, we present a case of IF that presented in the inguinal region-proximal thigh and was initially thought to be a kaposiform hemangioendothelioma (KHE) because it presented with a bleeding diathesis thought to be Kasabach-Merritt phenomenon (KMP). Subsequently, the placental examination showed a neoplasm in the perivascular-subendothelial space of stem villi, initially thought to be myofibromatosis. Ultimately, a biopsy of the thigh mass showed IF with an NTRK3-ETV6 fusion. Subsequent FISH analysis of the placenta showed an ETV6 rearrangement confirming that it was also IF. Review of the laboratory studies suggests that disseminated intravascular coagulation may have been more likely than KMP, highlighting the difficulty in making this distinction in some cases. We believe this to be the first report of an IF presenting in a soft tissue site and the placenta, and discuss the possible mechanisms that could have allowed the IF in the leg to spread to the placenta.

A Malignant Mimicker: Features of Kikuchi-Fujimoto Disease in the Pediatric Population.

BACKGROUND: Kikuchi-Fujimoto disease (KFD) is a rare, benign, and self-limited disease that presents with cervical lymphadenopathy and systemic symptoms. Histologic evaluation is often necessary to differentiate KFD from other entities. METHODS: Electronic medical records and diagnostic material were reviewed for 14 children diagnosed with KFD and 6 children diagnosed with infectious mononucleosis (IM) from 2013-2021. Four cases of KFD were further characterized using targeted DNA-based next-generation sequencing. RESULTS: Systemic symptoms were present in 86% (n = 12/14) of KFD patients, the most common being fever. Laboratory values worrisome for malignancy included cytopenia(s) (n = 9/12), elevated ESR and/or CRP (n = 9/12), elevated ferritin (n = 7/7), and elevated LDH (n = 7/10). Histologically, lymph nodes showed characteristic necrotic foci without neutrophils surrounded by MPO+ "crescentic" histiocytes. Immunoblasts and CD123+ plasmacytoid dendritic cells (pDCs) were also increased surrounding the necrosis. IM lymph nodes showed similar features when necrosis was present but increases in pDCs were patchy and rare neutrophils were seen in the necrotic foci. Molecular analysis of 4 KFD cases did not identify pathogenic variants. CONCLUSION: While the signs/symptoms of KFD are worrisome, there are pathologic features that help differentiate it from potential mimics. We did not identify characteristic molecular features to aid in the work-up of these cases.

Chondroblastoma of the Occipital Bone With Atypical Genetic Markers: A Case Report.

Chondroblastoma is a rare bone tumor, most often found in epiphyseal plates of long bones. It has infrequently been reported in the skull, most often in the temporal bone. We present a case of chondroblastoma of the occipital bone in a pediatric patient presenting with a bony protuberance of the occiput and imaging consistent with obstructive hydrocephalus, which persisted even after removal of the obstructing tumor. Pathological examination demonstrated that this unusually placed tumor also lacked the classic genetic markers typically associated with chondroblastoma.

Two cases of pineal anlage tumor with molecular analysis.

Pineal anlage tumor is a rare pediatric tumor with clinical and histological features overlapping with pineoblastoma. Two patients with pineal anlage tumor, a 13-month-old female and an 11-month-old male, underwent subtotal resection, high-dose chemotherapy with autologous stem cell rescue, and radiation. Neither had tumor progression 50 months after diagnosis. The tumors underwent next-generation sequencing on a panel of 340 genes. Chromosomal copy gains and losses were present and differed between the tumors. No mutations or amplifications, including none specific to pineoblastoma, were identified.

Clinical Outcomes of Diffuse Sclerosing Variant Papillary Thyroid Carcinoma in Pediatric Patients.

OBJECTIVES/HYPOTHESIS: The diffuse sclerosing variant of papillary thyroid carcinoma (DSV) may be more aggressive than conventional well-differentiated non-DSV related papillary thyroid carcinomas (N-PTC). STUDY DESIGN: Retrospective chart review. METHODS: Retrospective review of clinical outcomes for patients 21 years of age or younger who underwent initial surgery for PTC at a single institution from January 1, 2005 to April 1, 2020. Genomic analysis was performed using targeted next-generation sequencing. Data were analyzed using Fischer's exact test and Kaplan-Meier curve log-rank test. RESULTS: Our cohort consisted of 72 patients, nine with DSV and 63 with N-PTC. Age at diagnosis was comparable (15.4 vs. 16.2 years, respectively, P = .46). DSV were more likely to be in the high-risk American Thyroid Academy pediatric risk group (100% vs. 41.3%, P = .004), to present with regional cervical lymph node metastases (100% vs. 60.3%, P = .036), and to present with distant metastases (67% vs. 22%, P = .005). No mortality seen in either group over 27.5 (interquartile range 14.8, 46.00) months average follow-up. Throughout the follow-up period, DSV were more likely to experience progression than N-PTC (hazard ratio = 5.7 [95% confidence interval 1.7-20.0; P = .0056]). In a subset of 19 patients with aggressive disease who had molecular testing as part of clinical care we detected RET fusions in nearly all DSV compared to a minority of N-PTC (83% vs. 15.4%, P = .0095). CONCLUSIONS: Pediatric patients with DSV have more advanced disease at diagnosis and are more likely to experience progression of disease compared to patients with N-PTC. The prevalence of RET fusions in our cohort recapitulates the frequency of this alteration described in prior studies. LEVEL OF EVIDENCE: 4 Laryngoscope, 132:1132-1138, 2022.