Instability at sequence repeats in melanocytic tumours

To obtain information on the prevalence of microsatellite mutations in mela nomas, we analysed the status of 14 repetitive loci characterized by struct urally different noncoding and coding sequence repeats in a panel of 34 pri mary melanocytic tumours and in lymph node metastases matched to 13 cases, Instability at one or more of the non-coding dinucleotide repeats D2S123, D 3S611, D5S107 and D18S34 was detected in ten out of the 34 primary tumours (29%) and in ten of the 13 metastases (77%). There was no instability at th e non-coding mononucleotide repeats BAT25, BAT26 and AP Delta3 or at the co ding mononucleotide runs within the TGF beta RII, IGFIIR, BAX, hMSH3 and hM SH6 genes, A five-repeats expansion of the coding E2F4(CAG)n run was found in the only malignant melanoma of soft parts examined, which also showed in stability at two dinucleotide loci, and in a superficial spreading melanoma , which was stable at the mononucleotide and dinucleotide repeats but was t he only tumour that manifested instability at the SCA1(CAG)n repeat. The ab sence of mutations at mononucleotide tracts indicates that, in the malignan t melanomas tested, microsatellite instability was not associated with the microsatellite mutator phenotype characteristic of mismatch repair-deficien t tumours, On the other hand, our results confirm that microsatellite insta bility at dinucleotide repeats increases with melanoma progression, and ind icate that expansions of triplet repeats may occur in melanocytic tumours, (C) 2001 Lippincott Williams & Wilkins.