Assessment of TERT promoter hypermethylation as a liquid biopsy biomarker in pediatric nervous system tumors

Abstract

Central nervous system tumors are considered the most common group of solid tumors among pediatric patients. Since 2016, the integration of molecular classification provided by methylation analysis has been gradually implemented as it offers more precise diagnostic information, ensuring appropriate clinical monitoring. Telomeres are sequences of 7000 to 9000 bases, with the 5'-TTAGGG-3' sequence repeated approximately 2500 times, located at the ends of chromosomes. During the cell division cycle, telomeres shorten due to oxidative stress. Telomere maintenance or extension is carried out by telomerase, which has TERT as a subunit. TERT expression is controlled by methylation levels in the promoter region, located 5' from the transcription start site. Liquid biopsy is a less invasive method that allows real-time detection of tumor DNA in the plasma or cerebrospinal fluid of patients, known as ctDNA, and its presence is related to the release into the bloodstream of DNA fragments from cells undergoing apoptosis or necrosis. Investigation of ctDNA along with methylation status could provide relevant information associated with tumor behavior. The aim of this study is to evaluate the methylation status of the TERT promoter as a biomarker in cerebrospinal fluid of pediatric patients diagnosed with CNS tumors. This analysis will be performed on cerebrospinal fluid samples, from which ctDNA will be extracted, followed by qPCR using primers and probes to amplify the CpG site (cg11625005) of the TERT gene. The methylation status of TERT in tumor samples will be verified using methylation data already obtained in the laboratory.