Lack of Extractable Carcinogens in the Skin of Patients With Multiple Precancerous Keratoses of Actinic Origin

Although it is well known that ultraviolet light exerts a potent carcinogenic effect upon the skin, it is not known whether this effect is exerted directly upon a chromosome or a gene, or whether it is exerted indirectly through the formation of a carcinogenic compound. Indirect evidence that ultraviolet light does not exert its carcinogenic effect through the formation of a chemical resembling the carcinogenic hydrocarbons was provided by the observations of Rusch, Kline and Baumann (8) when they showed that in contrast to the additive effect between different carcinogenic hydrocarbons there was no additive effect between ultraviolet rays and carcinogenic hydrocarbons. Unpublished experiments by these same authors giving direct evidence of the lack of formation of carcinogenic chemicals by ultraviolet irradiation showed that benzene extracts of irradiated mouse skin or of irradiation tumors failed to induce neoplasms when injected subcutaneously in corn oil. Similarly, Passey (6) was unable to demonstrate carcinogens in extracts of the skins of rats irradiated for 1 year with ultraviolet rays. The observations of these workers were made with relatively small amounts of material so there was a possibility of insufficient dosage. The possibility that the skin of patients with multiple precancerous keratoses of actinic origin might contain extractable carcinogenic chemicals was considered. The availability of relatively large areas of keratotic skin for extraction by washing with benzene offered the advantage of providing large amounts of material for exhaustive tests for possible carcinogenic activity. Furthermore, by repeatedly washing one side of the face with benzene and observing the incidence of carcinoma on that side as compared to the unwashed side it was reasoned that, if carcinogens were being formed, their presence would be reflected in a reduced incidence of cancerous change in the lesions on the washed side of the face. MATERIALS AND METHODS Selection o] patients .--Twelve patients with multiple precancerous keratoses of the face were selected. All of these patients had previously developed at least one carcinoma and most had developed several carcinomas in their keratoses. Except for one 9 year old boy with xeroderma pigmentosum and one young woman with delayed xeroderrna pigrnentosum, the patients were elderly people with typical multiple actinic keratoses or the so-called "farmers' skin" or "sailors' skin". The patients were given a supply of 2 X 2 inch gauze pads and a supply of benzene. They were instructed to wash one side of their faces with the benzene and to save the pads used for this purpose in a large bottle. The procedure was repeated daily for periods of from 20 to 706 days with an average period of 162 days. In addition, small amounts of skin washings and excised keratoses from 25 other patients with multiple keratoses were pooled for extraction with benzene and assay for carcinogenic activity. In most cases, a record was kept of the size and location of the keratoses on both sides of the face so that any change in size or development could be followed. Preparation o] the extract . -The pads containing the skin washings were continuously extracted with hot benzene in a Soxhlet extractor for a minimum of 8 hours. The benzene extract was then concentrated by heating over a water bath under vacuum. The final product was a thick yellow or brown oil which became semisolid in the refrigerator. Tests /or carcinogenicity.--The concentrated material made from the skin washings was tested for carcinogenicity in mice by the following means: (a) painting on the skin in benzene solution (b) painting on the skin in combination with croton oil (c) painting on the ear plus irradiation wiih ultraviolet light, and (d) subcutaneous injection in mice and rats; in addition whole keratoses were implanted subcutaneously.