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WHO Classification of Tumours


Tricholemmoma (TL) is a benign cutaneous proliferation arising predominantly on the face. It usually presents as a small (3-8mm), solitary exophytic lesion which is either verrucous and keratotic or dome-shaped with a smooth surface. Histologically, TL presents as a sharply circumscribed, bulbous infundibular hyperplasia with tricholemmal differentiation. The infundibula show marked para- and hyperkeratosis and hypergranulosis and are surrounded by a collarette of adnexal epithelium. The tumour lobules consist of pale and clear isomorphic epithelial cells and are in continuity with the epidermis. The interfollicular epidermis is not involved. At the tumour periphery, there is a palisade of pale columnar cells, bordered by a prominent basement membrane.
Tricholemmoma occurs predominantly in adults. It is an entirely benign tumour; however, multiple TLs are frequently associated with Cowden disease , a search for internal malignancy is therefore indicated in these cases

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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