Desmoplastic malignant melanoma on the buttock of an 18-year-old girl - Differentiation from desmoplastic nevus

Melanocytic proliferation in young people may sometimes pose a diagnostic d ilemma. This is particularly so when a desmoplastic component is present. B ecause the two main differential diagnoses, desmoplastic malignant melanoma and desmoplastic Spitz nevus, share some morphologic features, the diagnos is of desmoplastic malignant melanoma may be overlooked. Distinction betwee n the two is important because they show completely different biological be havior. The age of patient, site of lesion, histologic findings of melanocy tic atypia, neurotropism, mitosis. and maturation help to distinguish the t wo entities. We report a case of desmoplastic malignant melanoma occurring in the buttock of an 18-year-old Chinese girl. Histologically, it had typic al features of desmoplastic malignant melanoma with junctional melanocytic atypia and prominent neurotropism. Clinical and histologic differences betw een desmoplastic malignant melanoma and desmoplastic Spitz nevus are review ed. We conclude that although desmoplastic Spitz nevus occurs much more com monly in adolescents, desmoplastic malignant melanoma can occur in this age group and even in non-sun-exposed skin. Microscopic findings remain the ma instay that guides the final diagnosis.