Significance of DNA abnormalities in primary malignant melanoma and nevi, a retrospective flow cytometric study.

DNA ploidy of melanocytic skin tumors from 87 patients (53 primary melanomas, 34 nevi) was determined by flow cytometry from routinely prepared paraffin blocks. Ploidy data correlated strongly with conventional morphological parameters. Only 1 of 34 nevi, but 13 of 53 melanomas were aneuploid. Among the melanomas, none of 21 levels I-III melanomas was aneuploid, but 13 of 32 levels IV and V melanomas were aneuploid. There was also a significant correlation between increasing Breslow thickness and the presence of DNA aneuploidy. For 33 melanoma patients with over 2 yr of follow-up (average, 7.1 yr), only 4 of 23 diploid tumors have recurred, but 9 of 10 aneuploid tumors have recurred. We conclude that the biological potential of melanocytic skin tumors is strongly linked to DNA aneuploidy. Since this parameter can be conveniently determined from paraffin blocks, determination of ploidy abnormalities in these tumors may be clinically useful.