Polypoid Spitz naevus: the benign counterpart of polypoid malignant melanoma.

Polypoid malignant melanoma is a peculiar morphological variant of melanoma with a distinct exophytic pattern of growth. This form of melanoma is usually very thick and the prognosis is accordingly poor. We present here a previously undescribed form of Spitz naevus which had a similar polypoid exophytic silhouette and marked cytological atypia. Despite these close morphological similarities, polypoid Spitz naevus evolves in a completely benign manner. Morphologically, polypoid Spitz naevus can be distinguished from polypoid melanoma by the absence of mitoses and by the prominent stromal reaction throughout the lesion.