CDKN2/p16 inactivation and p16 immunohistochemistry in astrocytic gliomas.

CDKN2/p16 inactivation is the most frequent alteration in the molecular regulation of G1-S transition. CDKN2/p16 homozygous deletions was studied in paraffin-embedded sections of 45 astrocytic tumours by multiplex PCR. Immunohistochemistry for p16 and proliferation marker Ki-67 MIB-1 was performed in adjacent sections; their labelling index (LI) have been calculated. CDKN2/p16 gene was not deleted in astrocytomas, while homozygous deletion was found in 26.7% anaplastic astrocytomas, and in 55.0% of glioblastomas. Analysis of CDKN2/p16 homozygous deletion in discrete areas of the same tumour, showed that the deletion occurred independently of the phenotypic aspect of the areas. Nevertheless a genotypic and phenotypic heterogeneity is present in few cases. p16 immunohistochemistry mostly corresponds to the genotypic pattern. No correlation was found between CDKN2/p16 homozygous deletion and MIB-1 LI.