Hematoxylin-eosin staining of the biopsy specimens revealed a well-preserved epidermis and a proliferation of fusiform cells in the dermis. The fusiform cells had an elongated nucleus and a prominent nucleolus, but did not contain noticeable pigment.
Immunohistochemical staining was performed. The results of cytokeratin staining (AE1/AE3 and CAM 5.2) were negative, but those of S100 protein and HMB-45 immmunostaining of both the nucleus and the cytoplasm were positive. The diagnosis of a nodular amelanotic melanoma with fusiform cells, 1.6 mm in thickness, was made. Lymphoscintigraphy and computed tomography revealed no abnormalities.
Nodular Lesion in a Kidney Transplant Recipient—Diagnosis. Arch Dermatol. 2003;139(9):1209-1214. doi:10.1001/archderm.139.9.1209-a