Mutation and allelic loss of the PTEN/MMAC1 gene in primary and metastaticmelanoma biopsies

The PTEN/MMAC1 gene on chromosome 10q23 encodes a lipid phosphatase with tu mor-suppressive properties. Germline PTEN/MMAC1 mutations have been implica ted as the predisposing factor in Cowden disease and other hamartoma syndro mes, and somatic mutations and deletions have been identified in a wide ran ge of human cancers, including 30-40% of metastatic melanoma cell lines. To study further the possible role of PTEN/MMAC1 in the pathogenesis and prog ression of malignant melanoma, we examined uncultured specimens from 16 pri mary and 61 metastatic tumors from 67 patients. Denaturing gradient gel ele ctrophoresis was used to analyze systematically the coding region of PTEN/M MAC1 and revealed mutations in four of the metastatic samples (7%). Sequenc e analysis of the mutants identified a 1 bp frameshift insertion, a 2 bp fr ameshift deletion, an 11 bp frameshift deletion, and a single base substitu tion resulting in the generation of a premature stop codon. Analysis of two intragenic polymorphisms showed allelic loss in three of eight informative primary tumors (38%) and in 18 of 31 metastatic tumors (58%). One of the m utant cases showed allelic loss, suggesting that both PTEN/MMAC1 alleles we re inactivated in this tumor. Altogether, these results suggest that mutati on and deletion of PTEN/MMAC1 may contribute to the development and progres sion of malignant melanoma.