High prevalence of p16 genetic alterations in head and neck tumours

inactivation of the p16 gene is believed to contribute to the tumorigenic p rocess of several neoplasms, including bead and neck tumours. In the presen t study, DNA samples from paired tumour and adjacent normal tissue from 47 patients with squamous cell carcinoma of the head and neck were investigate d for the occurrence of p16 genetic alterations. Single-strand conformation polymorphism and direct DNA sequence analysis led to the identification of p16 mutations in six cases (13%). Southern blot analysis showed that homoz ygous deletion is a rare event in the group of tumours analysed. Loss of he terozygosity (LOH) analysis was performed by polymerase chain reaction (PCR ) using two microsatellite markers (IFNA and D9S171) from the 9p21 region. Taking into account only the informative cases, 17 of 32 tumours (53%) show ed LOH for at least one of the markers analysed. The methylation status of the CpG sites in the exon 1 of the p16 gene was analysed using methylation- sensitive restriction enzymes and PCR amplification. Hypermethylation was o bserved in 22 (47%) of the head and neck tumours analysed. In our series of head and neck tumours, evidence for inactivation of both p16 alleles was o bserved in 13 cases with hypermethylation and LOH, two cases with hypermeth ylation and mutation, four cases with mutation and LOH and one case with ho mozygous deletion. These findings provide further evidence that genetic alt erations, especially hypermethylation and LOH, leading to the inactivation of the p16 tumour suppressor gene are common in primary head and neck tumou rs. (C) 1999 Cancer Research Campaign.