Cystic trichoblastoma: a report of two cases with an immunohistochemical study

We herein report two cases of cystic trichoblastoma with an immunohistochemical study. The histopathological findings in these cases included new information, namely, their being composed of two and three cysts, the cystic components had features of a steatocystoma and a hybrid cyst in one case, and there were projections of an aggregation of trichoblastoma, as well as papillary projections of follicular germinative cells, from the cyst walls. The follicular germinative cells observed in the papillary projections and in the aggregations of trichoblastoma expressed cytokeratin-15 (clone C8/144B) and PHLDA1, markers of follicular stem cells. Cystic trichoblastoma is a unique type of trichoblastoma, which originates from the cyst walls of an infundibular cyst (usually) or steatocystoma/hybrid cyst (rarely). In some cases, a trichoblastic infundibular cyst is considered to be a minor form (or possibly a primitive stage) of cystic trichoblastoma.