[Adenosquamous carcinoma of the skin--ultrastructural and immunohistochemical studies].

Adenosquamous carcinoma, which arose on the face of a 83-year-old woman was studied ultrastructurally and immunohistochemically. The tumor was composed of squamoid cells and mucinous cells including signet-ring cells. Electron microscopically, the tumor cells developed numerous microvilli on the cell surface, and had tonofilaments, well-developed rough endoplasmic reticulum and secretory granules of a mucinous type in the cytoplasm. The signet-ring cells had a large intracytoplasmic cavity containing fine fibrillar, mucin-like substance. Occasionally observed were intercellular masses, around which the tumor cells formed hemidesmosome-like and basal lamina-like structures. Immunohistochemical staining revealed foci of positive reaction for laminin surrounding the tumor cells. The tumor cells displayed positive stainings for stratified-epithelial keratins, but not for simple-epithelial keratins. From these findings, it was concluded that the present tumor might be a carcinoma of squamous cell origin, showing a mucinous metaplasia.