Rapid intraoperative molecular genetic classification of gliomas using Raman spectroscopy

Abstract

BACKGROUND The molecular genetic classification of gliomas, particularly identification of isocitrate dehydrogenase (IDH) mutations, is critical for clinical and surgical decision-making. Raman spectroscopy probes the unique molecular vibrations of a sample to accurately characterise its molecular composition. No sample processing is required allowing for rapid analysis of tissue. The aim of this study was to evaluate the ability of Raman spectroscopy to rapidly identify the common molecular genetic subtypes of diffuse glioma in the neurosurgical setting using fresh biopsy tissue. Additionally, classification models were built using cryosections, formalin-fixed paraffin-embedded (FFPE) sections and LN-18 (IDH-mutated and wildtype parental cell) glioma cell lines. METHODS Fresh tissue, straight from neurosurgical theatres, underwent Raman analysis and classification into: astrocytoma, IDH-wildtype; astrocytoma, IDH-mutant; or oligodendroglioma. The genetic subtype was confirmed on a parallel section using immunohistochemistry and targeted genetic sequencing. RESULTS Fresh tissue samples from 62 patients were collected (36 astrocytoma, IDH-wildtype; 21 astrocytoma, IDH-mutated; 5 oligodendroglioma). A principal component analysis fed linear discriminant analysis classification model demonstrated 79%-94% sensitivity and 90-100% specificity for predicting the three glioma genetic subtypes. For prediction of IDH mutation alone the model gave 91% sensitivity and 95% specificity. 79 cryosection, 120 FFPE samples and LN18 cells were also successfully classified. Mean time for Raman data collection was 9.5 minutes in the fresh tissue samples, with the process from intraoperative biopsy to genetic classification taking under 15 minutes. CONCLUSION These data demonstrate that Raman spectroscopy can be used for the rapid, intraoperative, classification of gliomas into common genetic subtypes.