CD-34 and Ki-67 staining patterns of basaloid follicular hamartoma are different from those in fibroepithelioma of Pinkus and other variants of basal cell carcinoma.

BACKGROUND AND AIMS: Basaloid follicular hamartoma is a rare disorder regarded as a developmental malformation. It may be solitary or generalized, linear or regionalized, and is sometimes associated with myasthenia gravis or alopecia. We compared immunohistochemical staining patterns of selected markers in order to differentiate this hamartoma from fibroepithelioma of Pinkus, a basal cell carcinoma variant it can be confused with.

METHODS: The expression of three immunohistochemical markers--CD-34, Ki-67, bcl-2--was studied in a basaloid follicular hamartoma and in a fibroepithelioma of Pinkus. Two basal cell carcinomas, a nodular and a fibrosing type, and a trichoepithelioma were included as controls.

RESULTS: Basaloid follicular hamartoma shows a low proliferation index and an at least focally circumferential expression of CD-34 around the epithelial strands. This compares to the findings in trichoepithelioma. In contrast, fibroepithelial tumor of Pinkus and two other basal cell carcinoma subtypes display a high proliferative index and an absence of CD-34 expression around the epithelium. These findings support the non-neoplastic nature of basaloid follicular hamartoma.