Morphology on spontaneous regression of the autochthonous colon carcinoma in WF Osaka rat strain.

In order to study the spontaneous regression of the colon cancers of WF Osaka strain rats, laparotomies were carried on 701 rats in sequence at the age of four months. Among them, 260 cases were found having colon cancers at the laparotomy. 107 out of them showed spontaneous regression of the colon cancer in the ascending colon. Most of the cases which spontaneously regressed were rather the early stage (stage 1 and 2) of the colon cancer, though 26 cases of advanced cancer also showed spontaneous regression. Grossly the lesions of the spontaneous regression were those of thickened, elongated ascending colon, with occasional dilation. Some cases showed the cystic formation at the portion of former lesions. There was a case which showed normal appearance of the ascending colon with regional lymph node metastasis measuring 1.5 x 1.5 centimeters. Histological appearance was varied showing reconstruction of the muscular layer and mucularis mucosae. Mucosal epithelium was almost normal looking, but glandular arrangement showed cystic dilation. The ectopic existence of glandular composition was seen in the restored lesion in the muscular layer. Macrophage infiltration was indispensably main histological reaction with central necrosis of formerly existed cancer cells, which was considered to be cellular immunity against cancer cells, or exogenous substances, such as viruses in cancer cells.