Trichogerminoma, a rare cutaneous follicular neoplasm with indolent clinical course: report of two cases and review of literature

Trichogerminoma is a rare cutaneous adnexal neoplasm of the hair germ cell and usually associated with benign clinical course and favorable outcome. Since its first description by Sau et al. in 1992, only a few cases have been reported up to date. Herein, we report two additional cases occurring in the hip and right thigh, respectively. Both patients are male, one is 78 years old, the other is 29 years old. Histological examination reveals well-circumscribed dermal nodule composed of lobules of basaloid cells with surrounding pseudocapsule. The distinct characteristic of the tumor is that most of the lobules display a special pattern of round nests or cell balls arranged in the central part with the peripheral palisading. Immunostaining showed ring-like fashion of CK5/6, P63 and Bcl-2 with negative or weak staining in the “cell balls”. There was no recurrence after complete excision during the period of follow-up. To the best of our knowledge, this is the first report of trichogerminoma in Chinese population. In contrast to the previously reported cases, ours present the similar morphological features with distinct immunohistochemical characteristics. We consider the concept of trichogerminoma exists with no doubt by its identifiable morphological features, and it should be classified as a variant of trichoblastoma. Because of its malignant potential, complete excision is a prior choice of treatment for this rare but distinctive tumor.