Heterogeneous Methylation and Deletion Patterns of the INK4a/ARF Locus Within Prostate Carcinomas

To elucidate the role of p53/p16^INK4a/RB1 pathways in prostate carcinogenesis, we analyzed the p14^ARF, p16^INK4a, RB1, p21^Waf1, p27^Kip1, PTEN, p73, p53, and MDM2 gene status of multiple areas within 16 histologically heterogeneous prostate carcinomas using methylation-specific polymerase chain reaction, differential polymerase chain reaction, and immunohistochemistry. All focal areas examined had Gleason scores ranging from 1 to 5. Methylation of either PTEN or p73 was undetected in any sample, whereas expression of MDM2 seemed to be an independent event within small foci of 4 of 16 tumors. Loss of p14^ARF, p16^INK4a, RB1, and p27^Kip1 expression correlated with homozygous deletion or promoter hypermethylation. One carcinoma showed co-deletion of both p14^ARF and p16^INK4a in two of five areas examined; two areas within another tumor demonstrated concurrent hypermethylation of the promoter regions of the same genes. Focal hypermethylation of RB1, p21^Waf1, and p27^Kip1 was detected within two, two, and three tumors, respectively. These findings indicate that both genetic and epigenetic events occur independently in intratumor foci and further suggest hypermethylation-induced loss of gene function may be as critical as specific genetic mutations in prostate carcinogenesis.