Cytokeratin 15 expression in neoplasms with sebaceous differentiation

Recent studies have demonstrated that the cytokeratin 15 (CK15)-positive stem cells located in the hair follicle bulge are also involved in sebaceous gland renewal. No previous studies have dealt with the CK15 expression in sebaceous neoplasms.

We studied the CK15 expression in 30 sebaceous neoplasms including 10 sebaceomas (sebaceoma defined as a distinct benign neoplasm with sebaceous differentiation), 10 sebaceous neoplasms of Muir-Torre syndrome, and 10 sebaceous carcinomas, in addition to that in the mantles of normal hair follicles.

CK15 was positive in the undifferentiated sebocytes of the mantles. All 10 sebaceomas showed CK15 expression in the basaloid, germinative cells. Both sebaceous neoplasms in Muir-Torre syndrome and sebaceous carcinomas demonstrated negative or only a focal positive reaction, including the occasional aberrant expression in matured sebocytes, to CK15.

CK15 may be a useful marker for stem cells with a sebaceous fate, and a constant CK15 expression in sebaceomas supported the hypothesis that sebaceoma is a benign neoplasm of sebaceous germinative cells in the mantles. The similar staining pattern of CK15 between sebaceous neoplasms in Muir-Torre syndrome and sebaceous carcinomas may be one piece of evidence supporting the hypothesis that most sebaceous neoplasms in Muir-Torre syndrome are low-grade sebaceous carcinomas.