Pilomatrix carcinoma arising from pilomatricoma after 10-year senescent period: Immunohistochemical analysis

Pilomatrix carcinoma is a rare malignant counterpart of pilomatricoma. To our knowledge, only approximately 90 cases have been published in English literature. Pilomatrix carcinoma is locally aggressive and occasionally shows rapid progression infiltrating to the muscle, bone and vessels. We report a case of pilomatrix carcinoma that developed in a 38-year-old man and started to grow after a long stable period, relapsed for a short time and infiltrated into the muscle underneath. While the initial skin biopsy showed histopathological findings consistent with pilomatricoma, the recurrent tumor contained marked cellular atypia and an aggressive growth pattern. Although it is still controversial whether pilomatrix carcinoma arises de novo or through malignant transformation of a pilomatricoma, the present case might be caused by the latter process considering the patient's clinical course. beta-catenin is a downstream effecter in the canonical pathway of Wnt, acting as a signal for cell differentiation and proliferation. The characteristic nuclear staining pattern of beta-catenin in the basaloid tumor cells, which is usually observed in pilomatrix carcinoma, supported the diagnosis of pilomatrix carcinoma in the present case.