Induction of oral cavity tumors in F344 rats by tobacco-specific nitrosamines and snuff

The tumorigenic activities toward the oral cavity of snuff, its extracts, and two of its major nitrosamines, N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were evaluated in male F344 rats. In one protocol, groups of 21-30 rats were treated beginning at age 10 weeks by chronic application to the oral cavity for 131 weeks of either H₂O, and H₂O extract of snuff, an H₂O extract of snuff enriched with ten times its indigenous concentration of NNN and NNK, or with NNN and NNK in H₂O. The incidence of oral cavity tumors in the rats treated with NNN and NNK was 8 of 30, compared to 0 of 30 in controls (P < 0.05). These results demonstrate that NNN and NNK can induce tumors locally in the oral cavity of F344 rats. Oral cavity tumors were also observed in 3 of 30 rats treated with snuff extract enriched with NNN and NNK, but not in the rats treated with snuff extract alone. In a second protocol, a test canal was surgically created in the lower lip of groups of 21-32 rats, and either snuff, H₂O-extracted snuff, or snuff enriched with its own H₂O extract was inserted in the test canal 5 times weekly for 116 weeks. A group of 10 control rats had surgery only. Among the 32 rats treated with snuff, 3 had oral cavity tumors; one was squamous cell carcinoma originating in the test canal and invading the gingiva, one was a papilloma of the test canal, and one was a papilloma of the hard plate. Oral cavity tumors were also observed in 2 of 21 rats treated with H₂O-extracted snuff and 1 of 32 rats treated with snuff enriched with its H₂O extract. Oral tumors were not observed in control rats. The results of this study indicate that snuff and individual nitrosamines present in snuff can induce oral cavity tumors in F344 rats and support the epidemiological observations which indicate that snuff dipping causes oral cancer in man.