DIAGNOSTIC IMPACT OF NUCLEAR-DNA CONTENT AND PROLIFERATIVE ACTIVITY IN BENIGN AND MALIGNANT MELANOCYTIC LESIONS

Nuclear DNA content was assessed, using image cytometry, in adult mela nocytes in normal skin and in 20 intradermal naevi, 60 junction naevi, 107 compound naevi, 61 dysplastic naevi, 17 melanomas in situ and 101 primary malignant melanomas. Proliferation was estimated using mitoti c counting and immunohistochemical staining by anti-Ki-67 (clone MIB1) monoclonal antibodies, All normal adult melanocytes and intradermal n aevi (97% junction naevi, 98% compound naevi, 66% dysplastic naevi) we re diploid. Thirty-four percent of the dysplastic naevi, 88% of the me lanomas in situ and 96% of the malignant melanomas were clearly aneupl oid. Proliferation, as assessed by mitotic counting and MIB1 index, wa s significantly higher in aneuploid invasive malignant melanomas than in aneuploid dysplastic naevi (P < 0.0001). The results indicate that histomorphologically defined entities of melanocytic lesions are chara cterized by typical DNA distribution patterns. Distinct aneuploidy com bined with high proliferation rates generally seem to be well correlat ed to an increased malignancy potential of the lesion. In dysplastic n aevi, the clonic expansion of aneuploid naevus cells may be limited by host defence mechanisms. Thus, DNA aneuploidy seems to indicate incre ased risk of malignant transformation, but has to be combined with oth er data, such as proliferation, in order to differentiate more precise ly between different melanocytic lesions.