A case of Basaloid Follicular Hamartoma

We here describe a case of solitary basaloid follicular hamartoma (BFH) : the case developing in company with senile lentigo on the nose. BFH is a relatively rare benign follicular neoplasm of undetermined etiology. Histologically, the specimen consisted of small-sized squamoid or basaloid cells and follicular germ-like cells in the periphery of the tumor nests. There were no infundibular cysts. BFH should be differentiated from infundibulocystic basal cell carcinoma (BCC), which consists of squamoid or basaloid cells in company with infundibular cysts, tumor of follicular infundibulum or trichoepithelioma. We analyzed the immunohistochemical findings of the case in comparison with those of BCC and trichoepithelioma. An immunohistochemical examination revealed 1) that Bcl-2 and CD10 was preferentially expressed in the outermost cells in the tumor nests consisting of follicular germ-like cells, 2) that most of the tumor cells, especially germ-like cells, were strongly positive for Ber-EP4, and 3) that peritumoral stroma was positive for CD34. The immunohistochemical findings of our cases supported that BFH should be differentiated from BCC, a common malignant neoplasm.