Separating the wheat from the chaff

Biomarkers are en vogue. Although few ever prove to be of practical value or find their place in routine clinical testing, occasionally a biomarker of great importance is identified, a biomarker that tells us something fundamental about a disease or points us to a specific therapeutic intervention. One such biomarker in neurooncology is the codeletion of chromosomal arms 1p and 19q in oligodendrogliomas, which is highly associated with classic histopathology, and as such has aided diagnosis, and, importantly, identifies a type of brain cancer that grows slowly and responds to treatment. The recent discovery of a somatic mutation in isocitrate dehydrogenase genes (IDH) in infiltrative gliomas likewise stands out, predicting a favorable clinical outcome and shedding light on the molecular pathogenesis of these neoplasms.

In this issue of Neurology®, Labussière et al.¹ make the remarkable observation that 1p and 19q allelic loss is invariably associated with IDH mutations. In a cohort of 764 gliomas, those with codeletion of chromosome 1p and 19q had mutations of either IDH1 (92%) or IDH2 (8%), whereas only one third of tumors with variable partial deletions of 1p and 19q, …