FISH-BASED INVESTIGATION OF CDKN2A AND IFNA14 IN GLIOBLASTOMA

Abstract AIMS Glioblastoma (GBM) tumours have a dismal prognosis despite aggressive anticancer therapy. Deletion of CDKN2A is among the most common genetic changes in GBM (~50%) and has been strongly associated with worse prognosis. Next generation DNA sequencing had shown that deletion of IFNA genes (located proximal to CDKN2A) is also a major genetic event in GBM (~25%). Clinical Identification of in vivo state of these two genes might facilitate improved individualized therapeutics. METHOD Glioma tissue microarray consisting of 45 samples was used to assess the co-deletion of CDKN2A and IFNA14 genes simultaneously, using a novel three-color fluorescence in situ hybridization (FISH) probe. We examined the correlation between CDKN2A and p16INK4a protein expression detected using immunohistochemistry (IHC). RESULTS FISH analysis showed that 44% of the primary GBMs harboured homozygous deletions of both CDKN2a and INFA14. By contrast, all grade II and III gliomas, had either wild-type or amplified CDKN2A and INFA14. All samples that showed CDKN2A homozygous deletion (n=11) were negative for p16INK4a staining, while 20 cores that were positive for p16INK4a expression did not harbour CDKN2A deletion. Survival curves of primary GBMs suggested that both the co-deletion of CDKN2A/INFA14 and negative p16INK4a expression were associated with shorter survival time. CONCLUSIONS Our FISH/IHC analyses indicate a strong correlation between CDKN2A and p16INK4a protein expression in grade III/II glioma, suggesting that amplification of CDKN2A might act as a gatekeeper to reduce the incidence of grade IV. Our data also highlight the high frequency of CDKN2A/INFA14 co-deletion in GBM tumours that might together impact on survival time.