Answer: Pilomatirxoma

Histology: Sections show a well circumscribed lobulated lesion that is composed of variable amount of basaloid and ghosts cells and foci of calcification. The former component is dominant in evolving lesions, while the latter is dominant in mature ones. A fibrous pseudo capsule can be present. In evolving lesions, the basaloid component may exhibit brisk mitotic activity and may be difficult to differentiated form basal carcinoma, particularly on punch biopsy or fine needle aspirate.

Discussion: In mature pilomatrixoma foci of predominantly pilar keratinization can be seen with occasional cases also showing epidermoid keratinization. Some tumors may also contain melanin pigment. Foreign body giant cell reactions are often present usually surrounding sheets of ghost cells. Pilomatrixoma is a benign tumor that shows differentiation towards the hair matrix. The epidermis is normal and the tumor is in located in the dermis with occasional extension into the subcutis.