Comparative analysis of neovascularization in primary cutaneous melanoma and Spitz nevus.

Spitz nevus is a well-known histologic simulator of malignant melanoma. Vascularity of human neoplasms has been associated with prognosis as well as propensity for metastasis. Were vascularity significantly different between melanoma and Spitz nevus, it could serve as a feature to distinguish between these two neoplasms. We evaluated the vascularity of a series of primary cutaneous melanomas ranging from thin superficial spreading to nodular lesions as well as superficial compound and nodular deep Spitz nevi by using light-microscopic evaluation of factor-VIII-stained sections. Vascularity was density graded and microvessels were counted per x200 and x400 field. Vascular density and microvessel counts were significantly different between melanomas of 2+ and 3+ vascularity compared with all types of Spitz nevi. Although nodular malignant melanomata tended to have a greater degree of vascularity than thin melanomas, there was a significant population of both of these subtypes having few or many vessels. We conclude that the number of microvessels per x200 and x400 field in areas of greatest vascularity is significantly less in Spitz nevus than in malignant melanoma. There is a subset of melanoma, however, in which the number of microvessels may be low. Nodular melanomata tended to have a greater number of vessels than did thin superficial spreading lesions. Evaluation of microvessel count may be of assistance when coupled with clinical and histologic findings in distinguishing between melanoma and Spitz nevus in selected cases.