Homozygous deletions of DMBT1 were found in 5% GBMs and 13% low-grade astrocytomas, but not in anaplastic astrocytomas. p16 suffered homozygous deletion in 27% GBMs and 13% low-grade astrocytomas, though no p16 point mutations were found in any of the 50 astrocytomas. p16 promoter hypermethylation was found in 9% GBMs and 6% low-grade astrocytomas.
Neither p53 expression nor p21 immunonegativity (52% of AAs and 48% of GBs) correlated with survival. p16 immunostaining was negative in 16% of AAs and in 44% of GBs, and it correlated inversely with survival in both uni- and multivariate analyses. pRb immunostaining was negative only in 8% of both AAs and GBs and the absence of p16 and pRb were mutually exclusive.
With quantitative multiplex polymerase chain reaction (PCR) assay using the exon 2 primers of the p16 gene and control chromosome 9qSTS primers, we found homozygous deletion of the p16 gene in 7 cases; in 1 out of 10 cases of anaplastic astrocytomas (WHO grade III), 6 out of 35 cases of glioblastoma multiformes (grade IV) but in none of the tumors of grade I or II.