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WHO Classification of Tumours
Pilomatrixoma, NOS
Skin


Definition

Pilomatrixoma is a benign adnexal neoplasm with differentiation towards matrix and inner sheath of the hair follicle and hair cortex. It chiefly develops in hair-bearing areas, mainly in the head and neck region and the upper extremities. Pilomatrixoma typically presents as a solitary, slow-growing, well-circumscribed, cystic or firm nodule measuring 0.5-3 cm in diameter. The histopathologic features differ depending on the stage of development. Early and well-developed lesions are lined focally by aggregations of basaloid and few squamoid cells; the cysts are filled with eosinophilic cornified material. Inflamed or regressing lesions contain prominent areas of ghost cells and foci of basaloid and/or squamoid cells surrounded by an inflammatory infiltrate. Old pilomatrixomas show no epithelial components but contain partially confluent ghost cell areas embedded in a desmoplastic stroma, with little or no inflammatory cells.
Pilomatrixoma occurs in all age groups; 30-50% of cases present in young adults <30 years of age. There is a predilection for women. Complete surgical excision is usually curative, but recurrences occasionally occur. Cases of spontaneous regression have been observed

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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



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