Development of tumours in Syrian hamsters during prolonged experimental exposure to nas.

In several series of experiments, nas was introduced into the buccal pouch or oesophagus of Syrian hamsters or applied to the dorsal skin. In one series, nas was administered to six consecutive generations of hamsters. No tumours appeared at the site of administration, although changes appeared in the mucosa of the buccal pouch and the oesophagus. Tumours in organs remote from the site of application developed only in those series in which nas was introduced into the buccal pouch. The commonest site of tumorigenesis was the liver, followed by the adrenal glands, the forestomach, and the genital organs. Tumours occurred in 17.6% of the experimental animals compared with 3.5% of the controls.