Electron microscopic observations on rat epidermis during experimental carcinogenesis.

Early ultrastructural changes and their progressive evolution were studied in rat epidermis following topical application of carcinogen (3-methylcholanthrene) and were compared to ultrastructural features of fully developed tumors (sebaceous epithelioma and basal cell epithelioma) in animals of the same group. Similar cytologic alterations were found, such as a marked increase in free ribosomes and polysomes, extensive endoplasmic reticulum, considerable increase of mitochondria, and dilated intercellular spaces, occupied by cytoplasmic projections. Predominance of dark cells, considered by us to be only phenotypically different from normal (light) cells, was also observed. A two-stage or multiple-stage of neoplastic evolution was suggested.