Disease Evolution Monitored by Serial Cerebrospinal Fluid Liquid Biopsies in Two Cases of Recurrent Medulloblastoma.

Medulloblastoma is the most common malignant brain tumor in childhood. Initial treatment generally includes surgery, irradiation, and chemotherapy. Approximately 20-30% of patients will experience a recurrence, which portends a very poor prognosis. The current standard of care for evaluation for relapse includes radiographic surveillance with magnetic resonance imaging at regular intervals. The presence of circulating tumor DNA in the cerebrospinal fluid has been demonstrated to be a predictor of a higher risk of progression in a research setting for patients with medulloblastoma treated on a prospective single institution clinical trial. We have previously published and clinically validated a liquid-biopsy-based genetic assay utilizing low-pass whole genome sequencing to detect copy number alterations in circulating tumor DNA. Here, we present two teenage patients with posterior fossa medulloblastoma with recurrent disease who have been monitored with serial liquid biopsies showing tumor evolution over time, demonstrating the clinical utility of these approaches.

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.

Cerebrospinal Fluid Liquid Biopsies in the Evaluation of Adult Gliomas.

PURPOSE OF REVIEW: This review aims to discuss recent research regarding the biomolecules explored in liquid biopsies and their potential clinical uses for adult-type diffuse gliomas. RECENT FINDINGS: Evaluation of tumor biomolecules via cerebrospinal fluid (CSF) is an emerging technology in neuro-oncology. Studies to date have already identified various circulating tumor DNA, extracellular vesicle, micro-messenger RNA and protein biomarkers of interest. These biomarkers show potential to assist in multiple avenues of central nervous system (CNS) tumor evaluation, including tumor differentiation and diagnosis, treatment selection, response assessment, detection of tumor progression, and prognosis. In addition, CSF liquid biopsies have the potential to better characterize tumor heterogeneity compared to conventional tissue collection and CNS imaging. Current imaging modalities are not sufficient to establish a definitive glioma diagnosis and repeated tissue sampling via conventional biopsy is risky, therefore, there is a great need to improve non-invasive and minimally invasive sampling methods. CSF liquid biopsies represent a promising, minimally invasive adjunct to current approaches which can provide diagnostic and prognostic information as well as aid in response assessment.

Optimization of a Protocol for Isolating Cell-free DNA From Cerebrospinal Fluid.

A standardized protocol for the isolation of cell-free DNA (cfDNA) from cerebrospinal fluid (CSF) is lacking. Therefore, we established a cfDNA isolation protocol optimized for clinical CSF specimens, integrating acceptable modifications and using artificial CSF generated from remnant CSF spiked with reference cell-free tumor DNA (ctDNA). We compared the isolation yields of in vitro diagnostic (IVD)-certified column-based (CB) and magnetic bead-based (MB) isolation. Furthermore, we modified both methods, including pre- and post-elution steps. To confirm ctDNA integrity and quantify the variant allele frequency after isolation, we performed droplet digital PCR (ddPCR) targeting IDH1 R132C in the reference ctDNA. MB isolation had a higher yield than CB isolation (P<0.0001), and post-isolation vacuum increased the final concentration in both methods, with little effect on cfDNA integrity. Our study provides a protocol to maximize CSF-ctDNA concentrations in IVD testing and future studies.

Liquid biopsy in the setting of leptomeningeal metastases: a systematic review and meta-analysis.

PURPOSE: The blood-brain barrier can prevent circulating tumor DNA (ctDNA) derived from the central nervous system from entering the blood making it challenging to evaluate molecular features of leptomeningeal metastasis (LM). Accordingly, we sought to systematically compare the diagnostic power or significance of ctDNA derived from cerebrospinal fluid (CSF) compared to plasma ctDNA in patients with LM. METHODS: A systematic review and meta-analysis was performed under the PRISMA guideline. We used PubMed, EMBASE, and the EuroPMC to search the literature using combinations of the following terms: circulating tumor DNA, ctDNA, circulating tumor cell, brain metastasis, leptomeningeal metastasis, outcome(s), and prognosis. We included all available English language studies that compared the diagnostic significance of CSF derived and serum ctDNA. All eligible studies level of bias was assessed using the New Castle Ottawa Scale (NOS). RESULTS: Our meta-analysis from 6 included studies (n = 226) that confirmed the diagnostic power of liquid biopsies in detecting genomic alteration is better when taking a CSF-derived samples than from the plasma (RR 1.46 [0.93; 2.29]; I2 = 92%; p-value < 0.01). CONCLUSION: CSF ctDNA is better at describing molecular landscape for LM; such an understanding may ultimately help inform patient treatment and responses to therapy.

Cerebrospinal fluid circulating tumour DNA genotyping and survival analysis in lung adenocarcinoma with leptomeningeal metastases.

PURPOSE: The prognosis of patients with leptomeningeal metastasis (LM) remains poor. Circulating tumour DNA (ctDNA) has been proven to be abundantly present in cerebrospinal fluid (CSF); hence, its clinical implication as a biomarker needs to be further verified. METHODS: We conducted a retrospective study of 35 lung adenocarcinoma (LUAD) patients with LM, and matched CSF and plasma samples were collected from all patients. All paired samples underwent next-generation sequencing (NGS) of 139 lung cancer-associated genes. The clinical characteristics and genetic profiling of LM were analysed in association with survival prognosis. RESULTS: LM showed genetic heterogeneity, in which CSF had a higher detection rate of ctDNA (P = 0.003), a higher median mutation count (P < 0.0001), a higher frequency of driver mutations (P < 0.01), and more copy number variation (CNV) alterations (P < 0.001) than plasma. The mutation frequencies of the EGFR, TP53, CDKN2A, MYC and CDKN2B genes were easier to detect in CSF than in LUAD tissue (P < 0.05), possibly reflecting the underlying mechanism of LM metastasis. CSF ctDNA is helpful for analysing the mechanism of EGFR-TKI resistance. In cohort 1, which comprised patients who received 1/2 EGFR-TKIs before the diagnosis of LM, TP53 and CDKN2A were the most common EGFR-independent resistant mutations. In cohort 2, comprising those who progressed after osimertinib and developed LM, 7 patients (43.75%) had EGFR CNV detected in CSF but not plasma. Furthermore, patient characteristics and various genes were included for interactive survival analysis. Patients with EGFR-mutated LUAD (P = 0.042) had a higher median OS, and CSF ctDNA mutation with TERT (P = 0.013) indicated a lower median OS. Last, we reported an LM case in which CSF ctDNA dynamic changes were well correlated with clinical treatment. CONCLUSIONS: CSF ctDNA could provide a more comprehensive genetic landscape of LM, indicating the potential metastasis-related and EGFR-TKI resistance mechanisms of LM patients. In addition, genotyping of CSF combined with clinical outcomes can predict the prognosis of LUAD patients with LM.

IDH1 p.R132H ctDNA and D-2-hydroxyglutarate as CSF biomarkers in patients with IDH-mutant gliomas.

INTRODUCTION: We aimed to evaluate IDH1 p.R132H mutation and 2-hydroxyglutarate (2HG) in cerebrospinal fluid (CSF) as biomarkers for patients with IDH-mutant gliomas. METHODS: CSF was collected from patients with infiltrating glioma, and 2HG levels were measured by liquid chromatography-mass spectrometry. IDH1 p.R132H mutant allele frequency (MAF) in CSF-ctDNA was measured by digital droplet PCR (ddPCR). Tumor volume was measured from standard-of-care magnetic resonance images. RESULTS: The study included 48 patients, 6 with IDH-mutant and 42 with IDH-wildtype gliomas, and 57 samples, 9 from the patients with IDH-mutant and 48 from the patients with IDH-wildtype gliomas. ctDNA was detected in 7 of the 9 samples from patients with IDH-mutant glioma, and IDH1 p.R132H mutation was detected in 5 of the 7 samples. The MAF ranged from 0.3 to 39.95%. Total 2HG level, D-2HG level, and D/L-2HG ratio in CSF were significantly higher in patients with IDH-mutant gliomas than in patients with IDH-wildtype gliomas. D-2HG level and D/L-2HG ratio correlated with total tumor volume in patients with IDH-mutant gliomas but not in patients with IDH-wildtype gliomas. CONCLUSION: Our results suggest that detection of IDH1 p.R132H mutation by ddPCR and increased D-2HG level in CSF may help identify IDH-mutant gliomas. Our results also suggest that D-2HG level and D/L-2HG ratio correlate with tumor volume in patients with IDH-mutant gliomas. Further prospective studies with larger cohorts are needed to validate these findings.

Usefulness of circulating tumor DNA from cerebrospinal fluid in recurrent high-grade glioma.

Molecular documentation at relapse of high-grade glioma is an urgent need for patient care. A prospective pilot study was conducted to assess the rate of mutation detection using targeted deep sequencing on circulating tumor DNA from cerebrospinal fluid (CSF) after chemo-radiotherapy based treatment. Fifteen patients were included: 13 patients with glioblastoma, 1 patient with gliosarcoma and 1 patient with anaplastic astrocytoma. At progression, 10/15 patients (67%) had detectable mutations in the CSF. Among them, 5/10 patients harbored at least one common mutation between initial tumor and ctDNA. CSF protein level and cfDNA concentration were higher, although not significant, in the ctDNA positive group versus ctDNA negative group (1.17g/L vs. 0.79g/L). Molecular documentation obtained from ctDNA in CSF at the time of relapse is informative in around two-thirds of the patients.

Circulating Tumor DNA in Adults With Glioma: A Systematic Review and Meta-Analysis of Biomarker Performance.

BACKGROUND: Circulating tumor DNA (ctDNA) has emerged as a promising noninvasive biomarker to capture tumor genetics in patients with brain tumors. Research into its clinical utility, however, has not been standardized because the sensitivity and specificity of ctDNA remain undefined. OBJECTIVE: To (1) review the primary literature about ctDNA in adults with glioma to compare the sensitivity and specificity of ctDNA in the cerebrospinal fluid vs the plasma and (2) to evaluate the effect of tumor grade on detection of ctDNA. METHODS: PRISMA-guided systematic review and meta-analysis was performed using published studies that assessed ctDNA in either plasma or cerebrospinal fluid among adult patients with confirmed glioma. Summary receiver operating characteristic curves were generated using the Rücker-Schumacher method, and area under the curve (AUC) was calculated. RESULTS: Meta-analysis revealed improved biomarker performance for CSF (AUC = 0.947) vs plasma (AUC = 0.741) ctDNA, although this did not reach statistical significance ( P = .141). Qualitative analysis revealed greater sensitivities among single-allele PCR and small, targeted next-generation sequencing panels compared with broader panels. It additionally demonstrated higher sensitivity of ctDNA detection in high-grade vs low-grade gliomas, although these analyses were limited by a lack of specificity reporting in many studies. CONCLUSION: ctDNA seems to be a highly sensitive and specific noninvasive biomarker among adults with gliomas. To maximize its performance, CSF should be studied with targeted genetic analysis platforms, particularly in high-grade gliomas. Further studies on ctDNA are needed to define its clinical utility in diagnosis, prognostication, glioblastoma pseudoprogression, and other scenarios wherein neoadjuvant therapies may be considered.

Liquid biopsy in CNS tumors: Current status & future perspectives.

Precise classification of central nervous system (CNS) malignancies is vital for the treatment and prognostication. Identification of noninvasive markers can be of importance to guide treatment decisions and in monitoring treatment response. CNS tumors are classified based on morphology with an essential complement of molecular changes, including mutations, amplifications, and methylation. Neuroimaging is the mainstay for initial diagnosis and monitoring tumor response with obvious limitations of imprecise tumor typing and no information on diagnostic, predictive and prognostic markers. Liquid biopsy has evolved as a diagnostic tool in body fluids and is being investigated as a surrogate for tissue biopsy in managing primary and metastatic brain tumors. Liquid biopsy refers to analyzing biological fluids such as peripheral blood, urine, pleural effusion, ascites, and cerebrospinal fluid (CSF); however, peripheral blood remains the primary source of fluid biopsy. The analytes include cell-free DNA (cfDNA) circulating tumor cells (CTCs), circulating micro RNAs (miRNAs), circulating proteins and extracellular vesicles (EVs). Analysis of these components is actively used for early cancer detection, auxiliary staging, prognosis assessment, detection of minimal residual disease (MRD), and monitoring drug resistance in various solid tumors. In recent years, liquid biopsy has been studied in CNS tumors, and analysis of CTCs and cfDNA have become relevant research topics. In the current review, we have explained the clinical potential of liquid biopsy in CNS tumors to assist in diagnosing and predicting prognosis and response to treatment.

Circulating tumor DNA profiling for childhood brain tumors: Technical challenges and evidence for utility.

Cell-free DNA (cfDNA) profiling as liquid biopsy has proven value in adult-onset malignancies, serving as a patient-specific surrogate for residual disease and providing a non-invasive tool for serial interrogation of tumor genomics. However, its application in neoplasms of the central nervous system (CNS) has not been as extensively studied. Unique considerations and methodological challenges exist, which need to be addressed before cfDNA studies can be incorporated as a clinical assay for primary CNS diseases. Here, we review the current status of applying cfDNA analysis in patients with CNS tumors, with special attention to diagnosis in pediatric patients. Technical concerns, evidence for utility, and potential developments are discussed.

Systemic Therapy for Lung Cancer Brain Metastases.

OPINION STATEMENT: Systemic therapy for brain metastases (BM) is quickly moving from conventional cytotoxic chemotherapy toward targeted therapies, that allow a disruption of driver molecular pathways. The discovery of actionable driver mutations has led to the development of an impressive number of tyrosine kinase inhibitors (TKIs), that target the epidermal growth factor receptor (EGFR) mutations, anaplastic-lymphoma-kinase (ALK) rearrangements, and other rare molecular alterations in patients bearing metastatic non-small cell lung cancer (NSCLC) in the brain, with remarkable results in terms of intracranial disease control and overall survival. Moreover, these drugs may delay the use of local therapies, such as stereotactic radiosurgery (SRS) or whole-brain radiotherapy (WBRT). New drugs with higher molecular specificity and ability to cross the CNS barriers (BBB, BTB and blood-CSF) are being developed. Two major issues are related to targeted therapies. First, the emergence of a resistance is a common event, and a deeper understanding of molecular pathways that are involved is critical for the successful development of effective new targeted agents. Second, an early detection of tumor progression is of utmost importance to avoid the prolongation of an ineffective therapy while changing to another drug. In order to monitor over time the treatment to targeted therapies, liquid biopsy, that allows the detection in biofluids of either circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) or exosomes, is increasingly employed in clinical trials: with respect to BM the monitoring of both blood and CSF is necessary. Also, radiomics is being developed to predict the mutational status of the BM on MRI.For patients without druggable mutations or who do not respond to targeted agents, immunotherapy with checkpoint inhibitors is increasingly employed, alone or in combination with radiotherapy. Pseudoprogression after immunotherapy alone maybe a challenge for several months after the start of treatment, and the same is true for radionecrosis after the combination of immunotherapy and SRS. In this regard, the value of advanced MRI techniques and PET imaging for a better distinction of pseudoprogression/radionecrosis and true tumor progression is promising, but needs validation in large prospective datasets. Last, a new frontier in the near future will be chemoprevention (primary and secondary), but we need to identify among solid tumors those subgroups of patients with a higher risk of relapsing into the brain and novel drugs, active on either neoplastic or normal cells of the microenvironment, that are cooperating in the invasion of brain tissue.

Detection of Leptomeningeal Disease Using Cell-Free DNA From Cerebrospinal Fluid.

Importance: Leptomeningeal disease (LMD) is a devastating complication of cancer that is frequently underdiagnosed owing to the low sensitivity of cerebrospinal fluid (CSF) cytologic assessment, the current benchmark diagnostic method. Improving diagnostic sensitivity may lead to improved treatment decisions. Objective: To assess whether cell-free DNA (cfDNA) analysis of CSF may be used to diagnose LMD more accurately than cytologic analysis. Design, Setting, and Participants: This diagnostic study conducted in a neuro-oncology clinic at 2 large, tertiary medical centers assessed the use of genomic sequencing of CSF samples obtained from 30 patients with suspected or confirmed LMD from 2015 through 2018 to identify tumor-derived cfDNA. From the same CSF samples, cytologic analyses were conducted, and the results of the 2 tests were compared. This study consisted of 2 patient populations: 22 patients with cytologically confirmed LMD without parenchymal tumors abutting their CSF and 8 patients with parenchymal brain metastases with no evidence of LMD. Patients were considered positive for the presence of LMD if previous CSF cytologic analysis was positive for malignant cells. The analysis was conducted from 2015 to 2018. Main Outcomes and Measures: The primary outcome was the diagnostic accuracy of cfDNA analysis, defined as the number of tests that resulted in correct diagnoses out of the total number of tests assayed. Hypotheses were formed before data collection. Results: In total, 30 patients (23 women [77%]; median age, 51 years [range, 28-81 years]), primarily presenting with metastatic solid malignant neoplasms, participated in this study. For 48 follow-up samples from patients previously diagnosed via cytologic analysis as having LMD with no parenchymal tumor abutting CSF, cfDNA findings were accurate in the assessment of LMD in 45 samples (94%; 95% CI, 83%-99%), whereas cytologic analysis was accurate in 36 samples (75%; 95% CI, 60%-86%), a significant difference (P = .02). Of 43 LMD-positive samples, CSF cfDNA analysis was sensitive to LMD in 40 samples (93%; 95% CI, 81%-99%), and cytologic analysis was sensitive to LMD in 31 samples (72%; 95% CI, 56%-85%), a significant difference (P = .02). For 3 patients with parenchymal brain metastases abutting the CSF and no suspicion of LMD, cytologic findings were negative for LMD in all 3 patients, whereas cfDNA findings were positive in all 3 patients. Conclusions and Relevance: This diagnostic study found improved sensitivity and accuracy of cfDNA CSF testing vs cytologic assessment for diagnosing LMD with the exception of parenchymal tumors abutting CSF, suggesting improved ability to diagnosis LMD. Consideration of incorporating CSF cfDNA analysis into clinical care is warranted.

Exploring genetic alterations in circulating tumor DNA from cerebrospinal fluid of pediatric medulloblastoma.

Medulloblastoma (MB) is the most common type of brain malignancy in children. Molecular profiling has become an important component to select patients for therapeutic approaches, allowing for personalized therapy. In this study, we successfully identified detectable levels of tumor-derived cell-free DNA (cfDNA) in cerebrospinal fluid (CSF) samples of patients with MB. Furthermore, cfDNA from CSF can interrogate for tumor-associated molecular clues. MB-associated alterations from CSF, tumor, and post-chemotherapy plasma were compared by deep sequencing on next-generation sequencing platform. Shared alterations exist between CSF and matched tumor tissues. More alternations were detected in circulating tumor DNA from CSF than those in genomic DNA from primary tumor. It was feasible to detect MB-associated mutations in plasma of patients treated with chemotherapy. Collectively, CSF supernatant can be used to monitor genomic alterations, as a superior technique as long as tumor-derived cfDNA can be isolated from CSF successfully.

Evaluation of the Oncomine Pan-Cancer Cell-Free Assay for Analyzing Circulating Tumor DNA in the Cerebrospinal Fluid in Patients with Central Nervous System Malignancies.

Available tools to evaluate patients with central nervous system (CNS) tumors such as magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) cytology, and brain biopsies, have significant limitations. MRI and CSF cytology have poor specificity and sensitivity, respectively, and brain biopsies are invasive. Circulating tumor DNA in CSF (CSF-ctDNA) could be used as a biomarker in patients with CNS tumors, but studies in this area are limited. We evaluated four CSF-ctDNA extraction methods and analyzed mutations in CSF-ctDNA with the Oncomine Pan-Cancer cell-free assay. CSF-ctDNA was extracted from 38 patients with primary or metastatic CNS tumors and 10 patients without CNS malignancy. Commercial ctDNA controls were used for assay evaluation. CSF-ctDNA yields ranged from 3.65 to 3120 ng. Mutations were detected in 39.5% of samples. TP53 was the most commonly mutated gene and copy number alterations were detected in CCND1, MYC, and ERBB2/HER2. Twenty-five percent of CSF-cytology-negative samples showed mutations in CSF-ctDNA. There was good concordance between mutations in CSF-ctDNA and matching tumors. The QIAamp Circulating Nucleic Acid Kit was the optimal method for extraction of CSF-ctDNA and the Oncomine cell-free DNA assay is suitable for detection of mutations in CSF-ctDNA. Analysis of CSF-ctDNA is more sensitive than CSF-cytology and has the potential to improve the diagnosis and monitoring of patients with CNS tumors.

Molecular diagnosis of diffuse glioma using a chip-based digital PCR system to analyze IDH, TERT, and H3 mutations in the cerebrospinal fluid.

PURPOSE: Conventional genetic analyzers require surgically obtained tumor tissues to confirm the molecular diagnosis of diffuse glioma. Recent technical breakthroughs have enabled increased utilization of cell-free tumor DNA (ctDNA) in body fluids as a reliable resource for molecular diagnosis in various cancers. Here, we tested the application of a chip-based digital PCR system for the less invasive diagnosis (i.e., liquid biopsy) of diffuse glioma using the cerebrospinal fluid (CSF). METHODS: CSF samples from 34 patients with diffuse glioma were collected from the surgical field during craniotomy. Preoperative lumbar CSF collection was also performed in 11 patients. Extracted ctDNA was used to analyze diagnostic point mutations in IDH1 R132H, TERT promoter (C228T and C250T), and H3F3A (K27M) on the QuantStudio® 3D Digital PCR System. These results were compared with their corresponding tumor DNA samples. RESULTS: We detected either of the diagnostic mutations in tumor DNA samples from 28 of 34 patients. Among them, we achieved precise molecular diagnoses using intracranial CSF in 20 (71%). Univariate analyses revealed that the World Health Organization (WHO) grade (p = 0.0034), radiographic enhancement (p = 0.0006), and Mib1 index (p = 0.01) were significant predictors of precise CSF-based molecular diagnosis. We precisely diagnosed WHO grade III or IV diffuse gliomas using lumbar CSF obtained from 6 (87%) of 7 patients with tumors harboring any mutation. CONCLUSION: We established a novel, non-invasive molecular diagnostic method using a chip-based digital PCR system targeting ctDNA derived from CSF with high sensitivity and specificity, especially for high-grade gliomas.

A nanowire-based liquid biopsy method using cerebrospinal fluid cell-free DNA for targeted management of leptomeningeal carcinomatosis.

PURPOSE: This study aimed to evaluate whether genotyping cell free DNA (cfDNA) in the cerebrospinal fluid (CSF) may be helpful in managing leptomeningeal carcinomatosis (LMC) of EGFR-mutant non-small cell lung cancer (NSCLC). METHODS: Patients with EGFR-mutant NSCLC who progressed as LMC after 3rd-generation tyrosine kinase inhibitors (EGFR-TKIs) were evaluated. A nanowire-based cfDNA assay was performed for genotyping cfDNA from the CSF and plasma. We focused on de novo EGFR C797S mutation and MET amplification, which are the most common mechanisms of resistance to 3rd-generation EGFR-TKIs. RESULTS: Among 11 patients, five (45.5%) had progression only at the leptomeninges. The tumor-associated CSF-cfDNA was identified in eight (72.7%) patients, and plasma-cfDNA in six (54.5%) patients. In the CSF-cfDNA, EGFR C797S mutation and MET amplification were detected in four (36.3%) and two (18.2%) patients, respectively. Of four patients with the C797S-positive LMC, only one had concurrent CSF-T790M mutation. Three patients who had the C797S-positive LMC without CSF-T790M mutation, received 1st-2nd generation EGFR-TKIs and showed clinical benefits for 20.8, 17.8, and 8.8 weeks, respectively. Serial assessment with cfDNA in these patients demonstrated that the CSF levels of C797S mutation were decreased with radiological or neurological improvement but the plasma levels of T790M mutation were markedly increased before objective progression. CONCLUSION: Genotyping CSF-cfDNA by the nanowire-based assay is feasible and effective in guiding the treatment of LMC in patients with EGFR-mutant NSCLC.

[Clinical Value of Cerebrospinal Fluid ctDNA in Patients 
with Non-small Cell Lung Cancer Meningeal Metastasis].

BACKGROUND: The mortality rate of lung cancer meningeal metastasis is extremely high. Circulating tumor DNA (ctDNA) has been confirmed to be contain the genomic alterations present in tumors and has been used to monitor tumor progression and response to treatments. Due to the presence of blood-brain barrier and other factors, peripheral blood ctDNA cannot reflect the information of brain lesions for patients with meningeal metastases. However, cerebrospinal fluid ctDNA as a test sample can better reflect the genetic status of intracranial tumors and guide clinical targeted treatment of intracranial lesions. This study explored the feasibility of cerebrospinal fluid ctNDA for evaluating non-small cell lung cancer (NSCLC) meningeal metastasis and the potential clinical value of cerebrospinal fluid ctDNA detection in NSCLC meningeal metastasis. METHODS: A total of 21 patients with NSCLC meningeal metastasis were included. Tumor genomic variation was performed on the cerebrospinal fluid and peripheral blood samples of patients by second-generation gene sequencing technology. The situation was examined, and pathological evaluation of cerebrospinal fluid cytology and head magnetic resonance imaging (MRI) enhanced examination were performed. RESULTS: ctDNA was detected in the cerebrospinal fluid of 21 patients. The sensitivity of cerebrospinal fluid ctDNA detection was superior to cytology in the diagnosis of meningeal metastasis (P<0.001). The detection rate and gene mutation abundance of cerebrospinal fluid were higher than plasma (P<0.001). Cerebro-spinal fluid had a unique genetic profile. In 6 patients with dynamic detection, changes of ctDNA allele fraction occurred at the same time or earlier than clinical disease changes, which could timely monitor drug resistance mechanism and relapse trend. CONCLUSIONS: The detection rate of ctDNA in cerebrospinal fluid is higher than that in cytology and imaging. The detection of ctDNA in cerebrospinal fluid can reveal the specific mutation map of meningeal metastasis lesions. The dynamic monitoring of ctDNA in cerebrospinal fluid has hint significance for clinical response of lung cancer patients.

Cerebrospinal fluid circulating tumour DNA as a liquid biopsy for central nervous system malignancies.

PURPOSE OF REVIEW: The molecular characterization of central nervous system (CNS) malignancies is crucial for obtaining the correct diagnosis and prognosis, and to guide the optimal therapeutic approach. However, obtaining surgical specimens can be challenging because of the anatomical location of the tumour and may limit the correct characterization of these malignancies. Recently, it has been shown that the cerebrospinal fluid (CSF) circulating tumour DNA (ctDNA) can be used as a liquid biopsy to characterize and monitor CNS malignancies and here we review its implications and advances. RECENT FINDINGS: In the last 5 years, several groups including ours have shown that ctDNA is highly present in the CSF, in larger amounts than in plasma, and that ctDNA can be sequenced to provide information about the diagnosis and prognosis of brain malignancies. Furthermore, the analysis of CSF ctDNA has allowed the selection of optimal therapeutic approaches monitoring response to treatment and tracking tumour evolution, providing crucial information about the molecular changes during tumour progression. SUMMARY: Here, we review the recent discoveries and data relative to CSF ctDNA and discuss how CSF ctDNA can be used as a liquid biopsy to facilitate and complement the clinical management of patients with CNS malignancies.