Animal type melanoma - A report of a case with balloon-cell change and sentinel lymph node metastasis

Animal type melanoma is a rare histopathologic variant of melanoma characte rized by sheets and nodules of heavily pigmented epithelioid melanocytes th at involve the entire thickness of the dermis. This human neoplasm mimics m elanocytic neoplasms seen in gray horses and laboratory animals; thus, is t ermed animal type melanoma. It is quite rare and, with only a few reported cases, its biological behavior is not well understood. We report an example of animal type melanoma on the back of a 27-year-old man. The lesion showe d areas of melanoma in sim, which ruled out the possibility of metastatic m elanoma. Features of regression were also seen at dermoepidermal junction a nd papillary dermis. In some areas, neoplastic melanocytes exhibited a ball oon-cell appearance; in others the neoplasm was composed of sheets and fasc icles of heavily pigmented epithelioid melanocytes that permeated the entir e dermis and extended into the dermal-subcutaneous interface, mimicking a c ellular blue nevus. Epithelioid melanocytes in deeper areas showed abundant , heavily pigmented cytoplasm and pleomorphic nuclei with prominent eosinop hilic nucleoli and some mitotic figures. The neoplastic cells did not show evidence of maturation in deeper areas of the lesion. In some sections, a n odule of heavily pigmented epithelioid melanocytes was seen far from the ma in bulk of the lesion, at the dermal-subcutaneous interface, raising the po ssibility of a satellite lesion. A lymphoscintigraphy showed a sentinel lym ph node in the right axilla and a subsequent axillary lymphadenectomy demon strated that the architecture of the sentinel lymph node was effaced by met astatic melanoma. The patient received adjuvant chemotherapy with inteferon alfa-2b and four months after this treatment the patient is alive and well , without evidence of recurrences or additional metastases.