Syringocystadenoma papilliferum on the male nipple

Syringocystadenoma papilliferum is a rare benign adnexal tumor that most frequently arises from an organoid nevus on the head and neck. Occurrence of this tumor on the male breast is extremely rare. A 74-year-old Japanese man presented with a nodule on his left nipple. Histopathological findings were typical for syringocystadenoma papilliferum. Ultrastructurally, constituent epithelial cells of the tumor were divided into three types. We focused on one cell type, undifferentiated clear cells, which have been suggested to be pluripotent cells bearing stem cell nature in syringocystadenoma papilliferum. Immunohistochemically, the tumor cells were negative for cytokeratin 15, which is known as a relatively specific marker for multipotent stem cells in the follicular bulge. We speculated that the clear cells are slightly differentiated toward apocrine rather than stem cells. We also ruled out the possibility of a relationship between the clear cells and Toker cells, which have a clear cytoplasm and are present in the areola region. Dermoscopic examination revealed amorphous milky white areas that corresponded to the pathological findings of luminal deposition of the tumor.