Keratoacanthoma with glandular proliferation

A case of keratoacanthoma (KA) with glandular proliferation was reported. The tumor was a firm, dome-shaped, elevated nodule on the cheek of an 82-year-old Japanese male. Generally, the tumor showed the typical histopathological features of KA; slight nuclear atypia and mitotic figures were present in a cup-shaped proliferation of keratinocytes and, in the center of the lesion, a keratin-filled crater with nests of dyskeratotic and acantholytic cells was seen. In the bottom of the lesion, a glandular structure forming branching, thin lumina was observed. The epithelium of the lumina was made up of two or more layers of columnar or cuboidal cells without keratinization. Tall columnar cells with oval nuclei were located in the luminal row and small cuboidal cells with round nuclei and scanty cytoplasm were in the outer layer. Immunohistochemical staining revealed that only the glandular structure was carcinoembryonic antigen positive. Lectin binding patterns observed in the glandular proliferation were similar to those reported for the apocrine gland. KA sometimes exhibits an adenoid structure in its lesion because of acantholytic changes. However, KA associated with true glandular proliferation has not been reported as far as we know, and our case is the first reported one. KA is thought to be a tumor of follicular origin, and the glandular proliferation observed in the present case seemed to have certain characteristics that suggest its apocrine origin.