Tar obtained by the combustion of cigarette tobacco at 500°–700° F. failed to demonstrate marked tumorigenic activity when applied to the skin of mice by the technic described.

Benzpyrene plus tobacco tar and benzpyrene plus croton oil have been demonstrated to produce a significantly greater proportion of papillomas and carcinomas following skin applications than benzpyrene alone.

The rate of development of carcinomas in mice with papillomas receiving benzpyrene plus tobacco tar was significantly greater than in mice treated with benzpyrene alone or with benzpyrene plus croton oil. From this action it is suggested that tobacco tar has a cocarcinogenic effect.

The obvious implications of these observations to the genesis of human bronchogenic carcinoma were discussed.

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This work was supported in part by an Institutional Grant from the American Cancer Society.

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