Aims: Recent studies have shown that most Dutch families with atypical multiple-mole melanoma (FAMMM) have a 19-bp deletion (p16-Leiden) in exon 2 of the p16 gene. Apart from reports on metachronous pancreatic tumors, other cancer types have never been described in such families. Due to heterozygous p16-Leiden constitution, our proband with multiple head and neck carcinomas was a suitable model for studying the type of p16 inactivation according to the Knudson-two-hit model.
Methods: p16 mutations in exons 1 and 2 were determined using PCR-SSCP-Sequencing analysis. p16 methylation was assessed by methylation-specific PCR.
Results: All three metachronous (larynx, pharynx, oral cavity) tumors had a methylated p16 promotor. The p16 protein loss detected by immunohistochemistry clearly confirmed a complete loss of p16 tumor suppressor function. Thus, all three tumors exhibited biallelic inactivation of p16, caused by aberrant methylation of the p16 promotor.
Conclusions: This is the first report on p16-Leiden mutation in head and neck cancer. We provide evidence that the somatic methylation of p16 promotor is associated with the germline transmission of p16-Leiden mutation. This is an example for the rare event of in which aberrant methylation acting as the 'second hit' in a familial cancer syndrome. Our results show that this epigenetic event is equivalent to genetic alterations (mutation/LOH) confirming the Knudson's hypothesis for tumor suppressor gene inactivation.