Malignancy of 4NQO-induced oral squamous cell carcinomas in the rat.

Oral carcinomas in the rat were induced by painting the hard palate three times a week for 22 weeks with the carcinogen 4-nitrochinoline N-oxide (4NQO). The induction resulted almost consistently in highly differentiated squamous cell carcinomas, often showing excessive keratinization. No metastases were recorded from any of the primary tumours. Transplantation experiments, performed on 23 out of a total of 26 induced carcinomas, generally yielded a negative result, only one tumour being transplantable. The biological significance of these features of 4NQO-induced oral rat carcinomas are discussed.