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

Background and aims: Basaloid follicular hamartoma is a rare disorder regar ded as a developmental malformation. It may be solitary or generalized, lin ear or regionalized, and is sometimes associated with myasthenia gravis or alopecia. We compared immunohistochemical staining patterns of selected mar kers in order to differentiate this hamartoma from fibroepithelioma of Pink us, 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 fibroepithe lioma 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 epitheli al strands. This compares to the findings in trichoepithelioma. In contrast , fibroepithelial tumor of Pinkus and two other basal cell carcinoma subtyp es display a high proliferative index and an absence of CD-34 expression ar ound the epithelium. These findings support the non-neoplastic nature of ba saloid follicular hamartoma. (C) Munksgaard 2001.