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CNS-associated tumors are notoriously difficult to detect in plasma. Chordomas are the most common primary spinal column malignancy, and extensive surgical procedures, along with chemotherapy and radiation are required to reduce recurrence. Currently CT, MRI, and PET are used to monitor for recurrence but are limited by surgical sequalae. In addition, needle biopsy risks tumor seeding along the biopsy track. In the largest cohort of chordomas described thus far, we characterize the mutational landscape of these tumors and show that liquid biopsy is a sensitive method for detecting cancers. 34 patients with a biopsy-confirmed diagnosis of chordoma had blood drawn before surgery, at the time of surgery, and/or at follow up appointments. Mutations in the primary tumor were identified by whole exome sequencing (WES) and droplet digital PCR (ddPCR) and/or Rapid Amplification of cDNA Ends Sequencing (RACE-Seq) was used to detect one or more of these mutations in plasma ctDNA at concurrent or later time points. The primary endpoint was detection of mutations in ctDNA in biopsy-confirmed chordoma samples. 87.9% of patients were ctDNA positive at the time of initial blood draw (p < 0.001). Follow up blood draws in twenty of the patients demonstrated that ctDNA levels reflected the clinical status of the disease. Patients with positive ctDNA levels were more likely to undergo radiotherapy (p = 0.004), and the presence of ctDNA may predict response to systemic chemotherapy and/or disease recurrence. Given the significant sequelae of biopsy and spinal surgery, liquid biopsy may be the best tool for detection and monitoring of chordomas.

Eight brain-derived proteins were evaluated regarding their potential for further development as a blood-based biomarker for malignant gliomas. Plasma levels for glial fibrillary acidic protein, neurogranin, brain-derived neurotrophic factor, intracellular adhesion molecule 5, metallothionein-3, beta-synuclein, S100 and neuron specific enolase were tested in plasma of 23 patients with high-grade gliomas (WHO grade IV), 11 low-grade gliomas (WHO grade II), and 15 healthy subjects. Compared to the healthy controls, none of the proteins appeared to be specific for glioblastomas. However, the data are suggestive of higher protein levels in gliosarcomas (n = 2), which may deserve further exploration.

Therapies that disrupt or repair blood-brain barrier integrity can result in major changes in MRI images even when the tumor volume remains constant. Thus, a reliable blood-based tumor biomarker could significantly improve clinical care and research studies in these patients. This study was performed to assess plasma concentrations of glial fibrillary acidic protein (GFAP) in patients with high- and low-grade gliomas before and after debulking surgery. Pre-operative plasma was collected from 33 patients with radiation- and chemotherapy-naïve gliomas. Additional plasma was collected 24-48 h post-operatively from 23 of these patients. Plasma GFAP (pGFAP) concentrations were determined using an electrochemiluminescent immunoassay and were analyzed as a function of tumor grade, tumor GFAP expression, the integrity of the blood-brain barrier, and post-operative status. Detectable pGFAP levels (≥ 0.04 ng/mL) were found pre-operatively in 52 % of patients and post-operatively in 96 %. Detectable pGFAP was more common in patients with WHO grade IV (100 %) than WHO grade III (56 %) or WHO grade II gliomas (20 %). No patient with undetectable GFAP had WHO grade IV glioma. Higher pGFAP concentrations were also associated with contrast enhancement but not related to tumor GFAP expression. GFAP is commonly detected in the plasma of patients with high-grade gliomas. pGFAP levels rise rather than fall following debulking surgery which is probably a result of surgical trauma. GFAP remains a potentially informative plasma biomarker for gliomas. Longitudinal studies are required to correlate pGFAP levels with patient outcomes.

BACKGROUND: Blood-based, circulating biomarkers play an important role in the detection and care for many cancer types. Such a biomarker is not clinically available for gliomas, even though there is pressing need for improved assessment of disease response and progression. The objective of this study was to explore eight potential biomarkers in their ability to discriminate among glioblastomas (WHO Grade IV), low grade gliomas (WHO Grade II), and healthy controls. METHODS: We collected pre-operative plasma from 34 patients with gliomas (WHO grade IV, n = 23; WHO grade II, n = 11), and we collected plasma from healthy subjects as controls (n = 15). Using enzyme-linked immunosorbent assays, we measured plasma concentrations of glial fibrillary acidic protein (GFAP), neurogranin, brain derived neurotrophic factor (BDNF), intracellular adhesion molecule 5 (ICAM-5), metallothionein-3 (MT3), beta-synuclein, S100B, and neuron specific enolase (NSE). RESULTS: The distributions of plasma protein concentrations demonstrated a high degree of overlap among WHO grade IV, WHO grade II, and healthy subjects. We found statistically significant differences between WHO grade IV tumors and healthy controls for ICAM-5 (p < 0.05, increased in grade IV) and BDNF (p < 0.05 decreased in grade IV), however not for the other markers tested. Whether blood was collected pre- or post-anesthesia affected some protein levels significantly (p < 0.05). We noticed that gliosarcomas (WHO Grade IV, n = 2) had substantially elevated levels of several biomarkers compared to glioblastomas and healthy subjects. CONCLUSIONS: Our analysis concludes that the eight circulating proteins are not glioma-specific biomarkers. Anesthesia may have an effect on plasma protein levels in plasma that future circulating biomarker studies should take into account. Gliosarcomas were under-represented in our sample, but they appear to have markedly higher levels of some of the studied proteins which deserves further evaluation.

2095 Background: Magnetic resonance imaging (MRI) of the brain primarily assesses blood brain barrier (BBB) dysfunction which provides indirect information regarding tumor size. The limitations of MRI have become evident with the use of temozolomide (pseudo-progression) and VEGF based therapies (pseudo-response). As a result, a blood-based marker to assess tumor burden is increasingly important. Previous studies suggested that plasma glial fibrillary acidic protein (GFAP) levels are sensitive and specific for glioblastoma (GBM). This pilot study examines the utility of GFAP as a biomarker in pre- and post-operative gliomas. Methods: Plasma samples were collected in patients pre-operatively (N=34) and 24-48 hours post-operatively (N=24) for what was post-operatively confirmed to be newly diagnosed glioma. Plasma GFAP was detected using an electrochemiluminescent immunoassay with a detection threshold of >0.04ng/ml. Presence or absence of contrast enhancement (CE) on the pre-op MRI was compared with the pre...