抄録
It is a well-established oncologic dogma that there are malignant equivalents of many tumors. This principle applies to putative tumors of the hair follicle. Benign pure epithelial tumors which differentiate into the outer root sheath (ORS) can be classified as trichilemmoma and proliferating trichilemmal tumor. The malignant counterparts of these tumors, if present, are malignant trichilemmoma (mTr) and malignant proliferating trichilemmal tumor, respectively. The criteria used for the histologic diagnosis of mTr have consisted of the presence of clear cells, glycogen-containing cells, and trichilemmal keratinization in the tumor nests. It has been unclear, however, whether these histologic features are specific for the tumors which differentiate into the ORS. We demonstrated that the above histologic features were noted in some cases of Bowen's disease which showed different phenotypes in keratin and involucrin expression from those of the ORS. Further immunohistochemical studies revealed that trichilemmoma and mTr showed similar immunophenotypes to the ORS, especially in the lower hair follicle which had characteristic expression of keratin and involucrin. Therefore, the immunohistochemistry of keratin and involucrin exprssion is useful for the identification and differentiation of mTr. By using immunohistochemical techniques, we should reexamine the diagnosis of the cases which have been diagnosed as mTr.
