Lack of complete 1p19q deletion in a consecutive series of 12 WHO grade II gliomas involving the insula: a marker of worse prognosis?

1p19q codeletion in WHO grade II glioma (GIIG) is claimed to be a marker of better outcome and chemosensitivity. Through the molecular study of 12 insular GIIG, our goal was to investigate a possible anatomo-molecular relationship in insula, specific brain sub-region, known to be involved with high frequency in GIIG. Loss of heterozygosity on 1p and 19q chromosomes was assessed in all tumors. None complete deletion of the 1p and 19q arms chromosomes and partial deletions in 3 patients were retrieved in the 11 WHO grade II oligodendrogliomas and one oligo-astrocytoma analyzed. Discrepancy between our results and the high reported incidence of 1p19q codeletion in oligodendrogliomas could mean that insular GIIG has a specific molecular pattern. We hypothesize that prognosis of insular GIIG is worse than in other locations, with reduced chemosensitivity. Thanks to minimization of surgical risks, surgery might be a first intention therapeutic option proposed in the GIIG.