[Microcystic adnexal carcinoma--a light and electron microscopic studies].

Microcystic adnexal carcinoma (MAC) in a 48-year-old Japanese male was studied. A firm nodule had appeared on the right side of his upper lip at the age of 38 years and then had gradually enlarged. Light microscopic examinations revealed numerous strands and islands of basaloid cells and keratinous cysts with desmoplastic stroma in the dermis and subcutaneous tissue. Some keratinous cysts showed early calcification and some contained pilar structures. Clear cells resembling sebaceous gland cells were observed in the strands of tumor cells connecting the keratinous cysts. In the middle dermis, there were small ductal structures containing amorphous eosinophilic material. Immunoperoxidase staining for carcinoembryonic antigen was focally positive in the lumina of small ducts, on the ductal lining surface of tumor cells, and in the contents of keratinous cysts. Electron microscopic examinations revealed tumor cells resembling non-keratotic keratinocytes, and containing tonofilaments, mitochondria, and vacuoles. In some parts, tumors were differentiated to various types of sebaceous gland, sweat duct, or sweat secretary segments. Sebaceous gland cells contained lipid droplets and glycogen. Tumors differentiated to sweat duct had a marked similarity to embryo eccrine duct in the lower epidermis because of the presence of multivesicular dense bodies and periluminal filamentous zones and the absence of myoepithelial cells. Tumors differentiated to sweat secretary segments had a similarity to embryo eccrine secretary segments because of the absence of multivesicular dense bodies, periluminal filamentous zones and myoepithelial cells.