Primary cutaneous nevoid melanoma with Homer-wright rosettes: a hitherto unrecognized variant with immunohistochemical and ultrastructural study.

We report a case of cutaneous nevoid melanoma manifesting as a growing and pruritic pigmented lesion of the back in a 43-year-old woman. The lesion measured 1.2 cm in its largest dimension. The salient microscopic features were discrete dermal nests of palisading tumor cells and a central fibrillary tangled core. Other features were microscopically consistent with melanoma: irregular tumor cell nesting associated with upward migration of melanocytes and consumption of the epidermal component, lack of maturation, expansile growth pattern, and a tendency to confluence of the dermal nests. No prominent mitotic activity was recognized. Breslow thickness was 1.3 mm. Tumor cells were positive for HMB45, Melan A, tyrosinase, and S100 protein. The MIB-1/ki-67 proliferative index was 2%. Histologic examination of a biopsy sample from the axillary sentinel lymph node was positive for small foci of melanocytic cells measuring 0.04 mm in their largest dimension.