Molecular diagnosis of oligodendroglioma in paraffin sections

Distinction of oligodendrogliomas from other gliomas is clinically important, but the histologic diagnosis of oligodendroglioma has been a difficult and notoriously subjective task. Testing for loss of heterozygosity (LOH) on chromosomal arms 1p and 19q, the genetic signature of oligodendroglioma, has emerged as a useful, objective adjunct to the traditional histologic evaluation. However, LOH testing of glioma specimens has not yet been widely implemented, presumably because of a lack of a practical LOH assay. We describe a 1p and 19q LOH assay suitable for routine diagnostics. In contrast to traditional microsatellite-based LOH analysis, we show that detection of LOH is usually possible even without normal tissue or blood from the same patient. A small area of tumor on a single paraffin section is sufficient for the assay. The assay protocol consists of a one-step DNA extraction, multiplex PCR for microsatellites on 1p and 19q, and capillary electrophoresis of the PCR products. LOH is detected by analysis of the allelic patterns and by integration of data from multiple highly polymorphic microsatellites. In a validation study on 19 gliomas, the results were concordant with results obtained by established methods and correlated well with histologic diagnoses. Because only a paraffin section is required, the pathologist can perform both the traditional histopathologic evaluation and this supporting molecular assay from the material at hand.