Melanoma metastases from patients with hereditary cutaneous malignant melanoma contain a high frequency of N-ras activating mutations.

Abstract

Mutations in N-ras exon 2 codon 61 were studied in formalin-fixed human melanoma metastases. DNA fragments including codon 61 were amplified by polymerase chain reaction (PCR) and mutational analysis was performed by oligonucleotide hybridization (ODN), allele specific PCR and PCR combined with single strand conformation polymorphism analysis (SSCP). Thirty metastases from 25 patients with 'spontaneous' cutaneous melanoma were compared with 35 metastases from 17 patients with 'hereditary' cutaneous melanoma. The frequency of mutations as measured by PCR/ODN was significantly higher in patients with hereditary melanoma (mutations in 24% versus 59%, p < 0.05). The most frequent mutations were C/A transversions to lysine (AAA). The occurrence of lysine mutations was, in addition, studied by allele specific polymerase chain reaction. Again, the mutation frequency was significantly higher in metastases from patients with hereditary melanoma. PCR/SSCP finally enabled the isolation of lysine mutant alleles and nucleotide sequence analysis which confirmed the presence of the mutated codon 61. The relatively higher frequency of N-ras mutations in tumours from patients with hereditary melanoma may be related to the hypermutability described in hereditary melanoma and dysplastic naevus syndrome. The results support an involvement of N-ras mutations in the molecular pathogenesis of melanoma.