Developments in molecular pathology testing for glioma

Abstract

Genetic analysis is now an integral part of glioma diagnosis and an essential aid to stratification of patient care (Louis et al., 2016). University Hospital Southampton is expanding its test repertoire to reflect these needs. The sensitive and specific technology of droplet digital PCR (ddPCR) can move Isocitrate Dehydrogenase (IDH) mutation testing away from current subjective immunohistochemistry (IHC) methodology. In a small study, 26 cases were tested by IHC, ddPCR and Sanger sequencing. Twenty cases were concordant for IDH R132H by IHC and ddPCR analysis, whilst three cases harboured the rarer IDH R132 or IDH2 variants, not evaluated by these two tests. However, three remaining IHC-IDH1 R132H negative cases were positive for IDH1 R132H by ddPCR, illustrating an improved sensitivity for IDH mutation testing using the digital PCR platform. Generic testing workflow for ddPCR, that meets ISO 15189 accreditation standards, facilitates a quick test work up for Single Nucleotide variant (SNV) mutation analysis. This can support clinical decision making vis-à-vis targeted therapy options and potential clinical trials entry. The use of microsatellite markers analysis provides an alternative method for the evaluation of 1p19q deletion characteristics. Investigation of O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation status using high resolution melt (HRM) brings this test in to our standard molecular laboratory workflow. Molecular testing for MGMT methylation status delivers results with fast turnaround time, supporting timely, evidence-based decisions for Temozolomide treatment. The PCR-based nature of these analyses have minimal tissue requirements and this suite of tests can be run on a single sample. Participation in the 100,000 genomes project is providing whole genome data with which to explore a 'one stop shop' approach to glioma molecular testing. In combination with DNA methylome analysis, we wish to evaluate the clinical utility of a pan-genome analysis for our glioma diagnostic and prognostic support service.