Chromosomal copy number changes supporting the classification of lentiginous junctional melanoma of the elderly as a subtype of melanoma

Recently the term lentiginous melanoma of the elderly has been suggested for a pattern of melanocytic neoplasia characterized by frequent occurrence in elderly patients, broad lentiginous growth pattern, with poorly cohesive nesting, suprabasilar extension of melanocytes and moderate cytological atypia. However, there are limited reported cases with follow-up information to confirm the malignant nature of these neoplasms. Using fluorescence in situ hybridization (FISH) targeting chromosomal loci that are frequently found to have copy number changes in melanoma, we evaluated cases of lentiginous junctional melanoma of the elderly in order to compare with the frequencies and patterns of chromosomal aberrations identified in other subtypes of melanoma. Previous studies have shown that by using a FISH assay targeting 6p25, 6q23, 11q13 and CEP6 with previously validated criteria, one could discriminate benign nevi from melanoma with high sensitivity and specificity. In this study, 16 of 19 cases (84%) showed sufficient copy number changes in one of the targeted chromosomal loci to meet FISH criteria for melanoma. A total of 17 control cases of lentiginous junctional nevi tested negative for all criteria. These findings support the classification of this pattern of melanocytic neoplasia as a subtype of melanoma.