[Proliferating trichilemmal cyst. Apropos of a case].

Malignant change in some keratinous cysts is a possible but rare condition. It seems acceptable that many publications concerning squamous cell carcinomas arising from previous cysts, actually correspond to the entity which Wilson-Jones called "proliferating epidermoid cyst" and they must be considered as pseudomalignant lesions, despite the presence of some features that may lead to a diagnosis of carcinoma. Although it is rare, which is nowadays called "proliferating Trichilemmal cyst", should be widely acknowledged since its misdiagnosis as squamous cell carcinoma leads to surgical treatment which is more drastic than necessary. Herein is presented an unusually situated case of proliferating Trichilemmal cyst and a review of the principal characteristics that have been pointed out in this tumor.