Aggressive pilomatricoma in childhood.

Pilomatricoma (calcifying epithelioma) is a benign tumor of the hair matrix cells that presents most frequently in childhood. Most are benign and slow growing and do not recur after excision. A small number of aggressive or malignant variants have been reported that recur if not widely excised. We report on an aggressive variant occurring in a 4-year-old boy and advise caution in treating cutaneous "cysts."