High frequency of homozygous deletion and methylation of p16INK4A gene in oral squamous cell carcinomas

p16INK4A inactivation was analyzed in ten squamous cell carcinoma (SCC) cell lines and 32 primary SCCs, using the polymerase chain reaction (PCR), PCR–single-strand conformation polymorphism, methylation-specific PCR, and cycle sequencing. In the study of cell lines, we detected three deletions in exon 1α and exon 2, and detected two methylations. Among tumor samples, we detected the homozygous deletions (HDs) of 43.8% in exon 1α 34.4% in exon 2, and methylation was found in 50.0%. The lack of p16INK4A with immunohistochemistry was detected in 71.9% and matched the alteration of p16INK4A gene. These results suggest that p16INK4A inactivation is predominantly caused by HD and methylation, and immunohistochemical evaluation of p16INK4A is a useful method.