[Human equine type melanoma: clinicopathologic study of 4 cases]

Four cases of human "equine" melanoma are presented. Two had poor prognosis, evidenced by the presence of metastases, and one of these with a rapidly fatal outcome. Human "equine" melanoma is characterized by an expansive, compact, heavily pigmented, dermal melanocytic proliferation without epidermal involvement. The mitotic index is always low, while minute foci of necrosis are present. The differential diagnosis is discussed, outlining the overlapping of the histological features with those of the malignant blu nevus. The only difference is the possible presence in the latter of areas characteristic of either common blu nevus or cellular blu nevus. With regards to the histogenesis of human "equine" melanoma we found no elements to support a follicular sheath origin and we propose a possible perineurial origin.