Sebaceous carcinoma with apocrine differentiation.

A 54-year-old male had a dome-shaped and skin-colored nodule on his nose. Histopathologically, we diagnosed this neoplasm as a low-grade sebaceous carcinoma rather than a sebaceoma based on the scanning magnification and cytology. This low-grade sebaceous carcinoma was associated with glandular structures. We regarded the glandular structures as those of apocrine glandular differentiation based on 1) the histopathologic features of the glandular structures formed by columnar luminal cells with evidence of decapitation secretion; 2) the expression of cytokeratin (CK) 19, CK8, CK8/18, and CK7 in the luminal cells; 3) the positive reaction of carcinoembryonic antigen and epithelial membrane antigen on the luminal surface and in the cytoplasm of the luminal cells; and 4) the common embryologic origin of the folliculosebaceous-apocrine unit. We found CK15 expression in undifferentiated cells within the mantles of normal hair follicles, suggesting that sebaceous stem cells might exist in mantles as follicular stem cells exist in bulge areas. Pluripotent stem cells in the folliculosebaceous-apocrine unit can give rise to follicular stem cells, sebaceous stem cells, and apocrine stem cells. Our patient's neoplasm showed apocrine glandular differentiation and partial immunohistochemical positivity for CK15 in the neoplastic aggregations. We believe this neoplasm originated from pluripotent stem cells destined to become sebaceous stem cells or from sebaceous stem cells, which also have the ability to differentiate within apocrine glands.