Multistage chemical carcinogenesis protocols produce spindle cell carcinomas of the mouse skin

Spindle cell carcinomas were identified using polyacrylamide gel electrophoresis and immunoblotting of proteins extracted from paraffin-embedded tissue sections. Immunohistochemistry using rabbit monospecific antisera against the mouse 55 kd keratin polypeptide also identified these tumors. A group of 53 SENCAR mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA) and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) yielded, after one year, four spindle cell carcinomas (0.07/mouse), whereas another group of 31 mice treated with a three-stage carcinogenesis protocol (initiation with DMBA and promotion for 10 weeks with TPA followed by 10 weeks of benzoyl peroxide) gave rise to six spindle cell carcinomas (0.19/mouse). The number of keratin-positive tumor cells and the intensity of the immunostain varied markedly, but all tumors expressed the 55 kd polypeptide. Although other carcinogens, mainly UV radiation, have been able to induce spindle cell tumors, the present data indicate that chemical carcinogenesis protocols are able to induce the formation of this highly malignant variant of skin carcinoma.