gms | German Medical Science

Objective: The clinical course of glioblastomas is mainly determined by the biological behavior of the tumor cells and their response to radiation and chemotherapy because a surgical cure is virtually impossible. Temozolomid (TMZ), a second-generation imidazotetrazine, increase the median survival time of patients with glioblastomas, especially those with deletions of the short arm of chromosome 9. The aim of our study was to investigate whether the tumor suppressor gene CDKN2A/p16 on 9p is responsible for the positive effect of TMZ of the survival time of patients with glioblastomas.

Methods: To investigate the deletions of CDKN2A on DNA level, we used two-color FISH with a centromere specific probe of chromosome 9 in combination with a gene specific probe for CDKN2A on paraffin embedded tissues. In order to correlate this with the loss of p16 on protein level, we performed immunohistochemical analyses with a specific antibody against p16. The possible inactivation of CDKN2A by hypermethylation of the promotor was analysed by methylation specific PCR.

Results: By FISH we found 8/19 cases with homozygous deletion of CDKN2A while 10/19 cases showed a heterozygous deletion of the gene. Patients with homozygous deletions had a decreased survival time (9.2 months) in contrast to patients with heterozygous deletions (20.4 months). The immunohistochemistry was performed on 20 paraffin embedded tissues of glioblastomas. Patients treated with TMZ chemotherapy showed an increased survival time in univariate analysis when they express p16 (p=0,06). In the same way patients with cytoplasmic expression of p16 had an increased survival time in contrast to patients who express p16 in the cell nucleus. The methylation specific PCR revealed an inactivation of CDKN2A by promotor hypermethylation in 5/45 cases.

Conclusions: This study demonstrates that the loss of CDKN2A/p16 might be correlated with a worse prognosis. However, these patients seem to respond to TMZ chemotherapy in an increased survival time. Further on, patients who still express p16 showed evidence for an increased survival time, especially when they express p16 mainly in the cytoplasm.