Proliferating Trichilemmal Tumor

**Semantic type:** Neoplastic Process

**Definition:** A neoplasm with tricholemmal differentiation. It affects women more frequently than men. It usually presents on the scalp as a solitary, multilobular, large, exophytic mass. Morphologically, it may display benign cytological features and appear as a circumscribed solid-cystic neoplasm or it may display malignant characteristics and invasive features. Cases without malignant characteristics usually have an indolent course. Complete surgical excision is recommended in such cases to avoid recurrences and to allow complete examination of the specimen. Cases with malignant characteristics may have a locally aggressive clinical course, recur, or metastasize.

**Synonyms:** - PTT - Pilar Cyst - Pilar Tumor - Pilar tumor - Proliferating Pilar Tumor - Proliferating Trichilemmal Cyst - Proliferating Tricholemmal Tumor - Proliferating trichilemmal cyst - Proliferating trichilemmal tumor