As the clinical and histological differential diagnosis between Spitz naevus and cutaneous
melanoma may be very difficult, we have investigated whether
DNA in situ hybridization maybe helpful in resolving this problem. To this end, routinely-processed
paraffin sections of 15 typical Spitz naevi, 15 typical nodular
melanomas, and five cases originally misdiagnosed as Spitz naevi but which later metastasized and were reclassified as
melanoma were analysed using a method previously described (De Wit et al., J Invest Dermatol 1992; 98: 450-458). Microscopical semi-quantitative evaluation revealed that the number of nuclei with supernumerary aberrations of the centromere region of chromosome 1, suggestive of
aneuploidy, was significantly different in Spitz naevi and nodular
melanoma. The mean number of aberrant nuclei per high power field was 0.41 and 4.01, respectively (P = 0.0001). On applying the results of the typical lesions to the equivocal, originally misdiagnosed lesions, three out of five could be identified as
melanoma. These results suggest that the application of
DNA in situ hybridization may contribute to the positive identification of histologically equivocal pigmented lesions. The advantages of this technique are that it is cheap, requires little tissue, and can be applied on routinely-processed
paraffin sections.