[Trichoblastoma. A tumor with follicular differentiation]

The purpose of this article is to inform about neoplasms with follicular differentiation, particularly trichoblastoma. In 1970 Headington divided neoplasms of the hair germ (trichogenic tumours) into four groups: purely epithelial without inductive changes (trichoblastomas), mixed epithelial-mesenchymal with inductive changes (trichoblastic fibromas), mixed epithelial-mesenchymal with inductive changes and advanced hair follicle formations (trichogenic trichoblastomas), and predominantly mesenchymal with an abortive dermal hair papilla (trichogenic myxoma). Meanwhile a new classification of neoplasms with follicular differentiation has been presented, according to which every neoplasm with follicular differentiation, benign structure (symmetrical, circumscribed, with vertical growth), and predominance of follicular germinative cells is called a trichoblastoma. Whether this neoplasm is malignant and if so to what degree is under discussion. This classification is gaining in acceptance among histopathologists but has not been accepted in the field of clinical dermatology.