[Pilomatrix carcinoma: histologic and immunohistochemical features. Two studies]

Malignant pilomatricoma is a rare malignant hair follicle tumor, that was initially described in 1980. Histologically, it shares common features with the more frequent, which benign pilomatricoma, makes its diagnosis difficult. It is a deep dermis-hypodermis epithelial tumor, well circumscribed, with no relation with the epidermis. It is composed of nodular structures with rows of basaloid cells in their periphery, as well as focal necrosis and mummified "ghost" cells in their central parts. Immunohistochemistry is of little value and can not confirm malignancy. The diagnosis remains essentially morphological. Histological examination must stress on the evaluation of the degree and extent of infiltration of the surrounding tissues, the degree of necrosis, the presence of atypical mitotic figures, and the presence or not of peri-neural or vascular invasion. Surgical wide resection is the recommended treatment. It reduces the risk of local recurrence by 50%. Malignant pilomatricoma carries a high risk of metastases to the bones, lungs, and lymph nodes. No feature is specific to confirm wether a malignant pilomatricoma arises de novo, or whether it is a malignant transformation of a pre-existing benign pilomatricoma.