Abstract
The reports of early cancer of the large intestine have been accumulated in Japan since the development of endoscopic polypectomy. We have defined the early cancer of the large intestine as that with involvement limited to the mucosa and the submucosa, as in the definition of the early cancer of the stomach. It was characteristic in previously reported cases that the shape of the early cancer that the size was within 10-20 mm and that a focal carcinoma was frequent. These findings suggested a close relationship between an adenoma and a cancer in the large intestine. An animal experiment was carried out to see an initial change of malignancy as an early cancer and to study endoscopical differentiation bet ween adenoma and early cancer. Polypoid lesions developed in the colon infusing a chemical car cinogen, MNNG, into the colons of the rats and rabbits were repeatedly observed by endos copy with proper intervals. 79 out of 97 rats survived for 30 weeks, and 175 polypoid lesions were found in 61 rats on necropsy. But in rabbits, significant polypoid lesions did not derelop for up to 80 weeks. The lesions of the colon appeared as a tiny flat prominence at first, and then gradually enlarged. As they grew, the shape changed from Yamada's Type I-II to Type III-IV. Spontaneos falling-off of 15 lesions of Yamada's Type III-IV was observed during this experiment. Histology of the 175 polypoid lesions of rats was : 20 carcinomas, 7 adenomas with severe atypia, 107 adenomas and 41 otherlesions. There was no difference in the endoscopic appearance of an adenoma and a cancer concerning redness, erosion and hemorrhage . But, as the polypoid lesions got bigger, focal atypism was more often recognized in histology. Scanning electron micrscopy performed on 3 adenomas and 3 cancers showed differences in opening pattern of pits and nature of the surfacc between an adenoma and a cancer.
