Cytogenetic analysis of melanocytes from premalignant nevi and melanomas.

We karyotypically analyzed cultured melanocytes from a variety of lesions, including congenital and dysplastic nevi, primary melanoma, and metastatic melanoma. The cells derived from congenital nevi had normal karyotypes, as did 22 of the 26 cultures derived from dysplastic nevi. The karyotypes of melanocytes from primary and metastatic melanomas were all abnormal. The only chromosome change in common between the nevi with abnormal karyotypes and the melanomas was the loss of one copy of chromosome 9 (two of four nevi and four of 11 melanomas, including three from the same patient) or the loss of the short arm of chromosome 9, especially of region 9pter-p22 (three of 11 melanomas). We suggest that deletion of a gene or genes on 9p, possibly interferon genes, is an initial step in the malignant transformation of melanocytes.