skin pilomatrix carcinoma
A very rare, locally aggressive, malignant neoplasm of the hair follicle. The majority of the cases arise de novo, however malignant transformation from a pre-existing pilomatricoma has been reported. It usually presents as a solitary nodule in the head and neck, upper extremities, or buttocks. Morphologically, it is characterized by the presence of aggregates of basaloid cells infiltrating the dermis. Masses of ghost cells are present in the cellular aggregates. Complete surgical excision is the treatment of choice. If it is not completely removed, it usually recurs, but it rarely metastasizes to distant anatomic sites.