Malignant Proliferating Trichilemmal Tumor

Abstract

Malignant proliferating trichilemmal tumor (MPTT) is a dermal or subcutaneous neoplasm with squamoid cytologic features and trichilemmal-type keratinization. The term MPTT was entered in the literature in 1983 because of a proliferating trichilemmal tumor that showed infiltrative growth pattern, marked cytologic atypia, high mitotic activity, and lymph node metastases. However, proliferating trichilemmal cyst (tumor) was first recognized by Wilson-Jones in 1966 as an entity that had the histological capacity to simulate squamous cell carcinoma, although its malignant potential has not been stressed. Alternatively, some authors have proposed that proliferating trichilemmal cyst “should always be considered as a low-grade squamous cell carcinoma,” and the term “proliferating follicular cystic SCC” has been proposed to encompass both conventional and malignant proliferating trichilemmal tumor. More than 30 cases of MPTT have been described in the literature, including 12 cases of metastatic disease, with several mortalities.