A case of secondary cutaneous amyloidosis: epidermal keratinocytes produce amyloid in the cytoplasm.

A case of secondary localized cutaneous amyloidosis associated with a seborrheic keratosis is reported. Amyloid was observed both in the stroma and in the tumor. Light and electron microscopy revealed amyloid within the cytoplasm of the tumor cells. This intracytoplasmic amyloid was seen in basaloid cells or in the border areas between basaloid cells and squamous cells, but it was not seen in squamous cells. The amyloid was positive for anti-keratin antibody and contained disulfide bonds. It is suggested that either abnormal keratinization or the degeneration of basaloid cells produced abnormal keratin proteins that formed this amyloid.