LIQUID BIOPSY IN Low-grade Glioma Patients

Diffuse low-grade gliomas (DLGG) (or WHO grade II gliomas) are rare tumors, with an incidence estimated at 1/105 person-year. DLGG are characterized by a continuous growth and an unavoidable anaplastic transformation. DLGG malignant progression is classically characterized by a continuum, from grade II to grade III or IV tumors.

To date, the histomolecular diagnosis of lower grade gliomas (that is, grade II and III gliomas) is achieved on tumor samples obtained from surgical resection or biopsy. Indeed, whereas brain MRI is often suggestive of DLGG, there is a need for a histological confirmation of diagnosis prior to any medical treatment. Moreover, MRI features to not always accurately predict the tumor grade, with grade II tumor presenting with contrast enhancement or non-enhancing authentic grade III tumors.

In this setting, the value of liquid biopsy (in blood or cerebrospinal fluid CSF) as a non-invasive, disease-associated biomarker has gained interest in the past decade, either at tumor diagnosis or to monitor tumor evolution in order to guide patient management and to detect changes of molecular features over time. While extracranial metastasis of glioma rarely occurs, recent reports suggest the possible presence of circulating tumor cells (CTCs) in blood of high-grade glioma patients. Beside CTCs, other circulating biomarkers have been recently investigated in glioma, including circulating tumor DNA, microRNA or tumor-educated platelet (TEP) RNA. Some of these techniques allow genome-wide characterization of RNA/DNA contents.

However, these studies are all small exploratory studies that have mainly included glioblastoma (grade IV glioma) patients rather than lower-grade gliomas, or glioma patients with no precision on tumor grade. Moreover, some of these studies analyzed samples performed after the patient received a medical oncological treatment (chemotherapy or radiation therapy). They advocate for the search of a circulating signature that would not be restricted to biomarkers directly derived from the tumor but include markers induced at a distance by the tumor. Indeed, slow-growing DLGG are likely to induce a systemic reaction to allow, for many years, an immuno-tolerance of the tumor. This reaction could have an impact on peripheral blood cells, including their RNA content.

In this study, the investigators aim at conducting an exploratory study in DLGG patients to explore the value of several blood-based biomarkers for the disease diagnosis and/or monitoring.