Pilomatrix carcinoma and multiple pilomatrixomas.

Pilomatrixoma is the only skin appendage tumour showing predominantly hair matrix differentiation. Rarely, aggressive or malignant variants are reported in the literature. We report a case of a 44-year-old male with multiple pilomatrixomas, one of which grew rapidly, recurring several times. Histological examination of this tumour showed predominantly hair matrix differentiation but also abortive hair follicle formation with pilar keratinization reminiscent of a trichoepithelioma. Numerous mitoses and moderate cellular pleomorphism were present, associated with infiltration of subcutaneous skeletal muscle and vascular invasion.