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WHO Classification of Tumours
Proliferating tricholemmal tumor


Proliferating tricholemmal tumour is a cutaneous neoplasm with tricholemmal differentiation. The great majority (>90%) of cases affect the scalp. The tumour presents as a large (2-10cm, rare cases up to 25cm), solitary, multilobular, exophytic mass. Morphologically, there is a continuum from benign to malignant features. Benign lesions are well-circumscribed, solid-cystic dermal masses that may extend into subcutaneous tissue. The cyst lumen contains prominent epithelial infoldings. The neoplastic cells are monomorphous and lack significant cytologic atypia. At the other end of the morphologic spectrum are lesions with malignant characteristics such as invasive growth, nuclear polymorphism, high mitotic activity, shadow and spindle cells.
Proliferating tricholemmal tumour predominantly arises in elderly patients and shows a predilection for women. 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

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LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
3rd Edition
IARC Press: Lyon 2005