Tobacco Documents Online

From the photographs of papillomas taken from representative animals after approximately 48 weeks of painting, it may be seen that these lesions have the typical appearance of tobacco tar-induced papillomas. No attempt was made to study their histological evolution from benign hyperplasia to cancer, but histological studies showed typical squamous cell carcinomas in a number of instances. Dis cus s ion It may be concluded that at high dosages, the condensates obtained from smoke of cigar-ettes with and without filter tips are capable of caus- ing papillomas and cancers in the skin of mice. This is in accordance with the earlier literature quoted extensively in our previous study on skin paint- ing of mice with tobacco smoke condensates derived from pipe, cigar and cigarette tobaccos (J. Nat. Cancer Inst. 31:1445-1459). The differences of carcinogenicity of equal amounts of such tars are minor. Nevertheless, there are tars produced by smoking through such filters as the Kent micronite filter which appear to have reduced carcinogenicity (as compared to unfiltered smoke) when applied to the skin of mice. This was not true in the case of another type of filter studied here which yielded tar of carcino- genicity equal to that of unfiltered smoke. The carcinogenicity of the condensates from smoke of the Kent cigarettes would then be considerably lower than that of the two other cigarettes when compared on a per-cigarette instead of on a per-weight basis. The most rapid development of skin papillomas was obtained with Fraction B. This is the carbon tetrachloride-eluted subfraction of the neutral tar and amounts to 1.7% of the crude tar. Wynder and Wright (Cancer 10:255-271, 1961) had noted marked biological activity in this fraction. Since at high dosage this B fraction causes much earlier appear- ance of papillomas, it may be considered to contain a highly active co- carcinogen and primarily appears to act as a promoter.

- 12 - Since the total tumor incidence obtained, 95% and 98%, is also higher than that seen with the tars themselves, it must be assumed that adequate amounts of initiators (polycyclic hydrocarbons) or other carcinogens are also present. The controls in this experiment showed a small incidence of papillomas (3. 3%); this suggests a slight contamination of acetone with some chemical carcinogen. This is minimal and insignificant. There was no significant difference in the mean body weights between animals with and without papillomas, receiving the same material. These biological tests strongly suggest the usefulness of an intensive search for cocarcinogens (promoters) in Fraction B. Elimina- tion of such substances might well reduce carcinogenic activity of tobacco tars down to insignificance.

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