Experimental colonic tumours in the rat. III. Induction time, distribution and appearance of induced tumours.

In 189 rats N-methyl-N'-nitro-N-nitrosoguanidine or 1,2-dimethylhydrazine (DMH) was given in order to induce colonic tumours. The tumour induction was followed by double contrast examination. At 894 examinations 196 adenomatous tumours were revealed. Autopsy and microscopy revealed 214 macroscopic and 53 microscopic benign or malignant adenomatous tumours. Metastases were found in 17 per cent in the DMH group. The relationship between adenomas and carcinomas is also evaluated.