A combined variant of Spitz's nevi. How to differentiate them from malignant melanomas

In the past several years we have studied 22 lesions of what we believe are combined variants of Spitz's nevi. Almost all of the patients were young adults. These combined melanocytic nevi have the architectural pattern of benign lesions, i.e., they are relatively symmetrical and well circumscribed. Each was characterized by the presence of at least two populations of nevus cells, one relatively banal with small nuclei and scant cytoplasm, the other with large nuclei and abundant cytoplasm. The latter are indistinguishable from cuboidal (epithelioid) cells of Spitz's nevus. The banal and the large nevus cells were intermingled in some of the lesions, but were segregated in others. Because these combined nevi differ from conventional Spitz's nevi and because the large nevus cells often fail to show maturation with progressive descent into the dermis, they are commonly misdiagnosed histologically as malignant melanomas.