Histopathological and experimental studies on development of gastric cancers

A mode of development of diffuse type cancers and adenocarcinomas was studied. Materials were small cancers endoscopically diagnosed, and minute cancers incidentally found in the gastric mucosa of resected human stomachs. In order to analyze initial lesions of signet ring cell carcinomas, we induced experimentally signet ring cell cancers in dog stomachs by administration of N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). From these studies, it was shown that both signet ring cell carcinomas and adenocarcinomas arise at the neck region of gastric glands. Signet ring cell carcinomas arise de novo from the stem cell of normal-looking glandular tubules. There were no precursor lesions for the development of this type cancer. Adenocarcinomas seemed to arise in the incompletely intestinalized glandular tubules or arise de novo at the neck region of pyloric glandular tubules. From mucin-immunohistochemical studies, it was found that about 23% of adenocarcinomas were gastric-type, 30% were intestinal-type and the remaining 47% were mixed of gastric and intestinal phenotype. phy, and BrdU(bromodeoxyuridine)/PCNA(proliferating cell nuclear antigen) immunohistochemistry were used. Mucin phenotypes of gastric cancers were assessed by immunohistochemistry using MUC2, MUC5AC, MUC6 and CD10 monoclonal antibody. Amplifications of several oncogenes and expression of oncogene products were also examined in the cancerous tissues and in the surrounding gastric mucosa, and its implications in carcinogenesis were discussed. MATERIALS AND METHODS 1. Minute cancers of human stomach From the resected stomachs documented at our Institute in the past 10 years, we collected very small diffuse type cancers and adenocarcinomas. The cancers less than 5mm in diameter were referred to as "minute cancer". The minute cancers were those found at the endoscopic examination, and they were the second lesion incidentally found in the stomachs resected for the primary cancer and ulcerative diseases. Some biopsied tissues were labeled with 3H-thymidine in vitro, processed for conventional autoradiography. Others were labeled with BrdU, processed for immunohistochemistry using anti-BrdU antibody. The cancer tissues and gastric mucosal sections, which were cut serially to study preand paracancerous lesions, were also immunohistochemically stained with PCNA antibody, for identification of proliferative cells. In these materials, we studied cell proliferation of gastric cancers and the gastric mucosa involved in chronic gastritis with or without intestinal metaplasia. Phenotypic expressions of gastric cancers, intestinal or gastric, were assessed with mucin histochemistry with Alcian blue, PAS and concanavalin A staining, and with immunohistochemistry using MUC2, MUC5AC, MUC6 and CD10. Amplification of c-erbB2, c-met and k-sam and expression of oncogenes and antioncogenes (c-ki-ras and p53) was examined in gastric cancer cells and in non-cancerous gastric mucosa. 2. Experimental signet ring cell carcinomas in dog stomach In order to examine a mode of development of signet ring cell carcinomas, we induced the cancers in dog stomachs with oral administration of ENNG, according to the method of Kurihara, et al. Male beagle dogs (1 year old, body weight 11-16kg) were given 75 mg of ENNG (Nacalai tesque, Kyoto Japan) with food, every day for 8 months. Five to 10 months after the ENNG administration, dogs were killed. Before sacrifice, they received single or multiple injections of 3H-thymidine and BrdU, with which cell proliferation of cancerous tissues and the background gastric tissues were studied, with autoradiographic and immunohistochemical methods. RESULTS AND DISCUSSION 1. Intramucosal distribution of initial signet ring cell carcinoma In the present study, it was found that tiny (very minute) signet ring cell carcinomas were distributed around the neck region of glandular tubules, and small signet ring cell carcinomas formed a layered structure, the upper and lower part of which were composed of typical signet ring cells, and the middle layer consisted of small round cells. The small round cells were confined to the neck region. The neighboring glandular tubules around the smaller signet ring cell carcinomas were not involved in intestinal metaplasia. A varying degree of inflammatory reaction was seen in the lamina propria, but no special change was seen. These findings indicate that signet ring cell carcinomas arise at the neck region of gastric glands, and there were no precancerous lesion for the development of signet ring cell carcinomas. 2. Initial lesions of signet ring cell carcinomas in dog stomach In the antral mucosa of several dogs treated with ENNG, in which no tumorous lesion was noted macroscopically, we found several initial signet ring cell carcinomas. In this, a very small cancer was seen at the neck region of glands; typical signet ring cells with mucin were seen at the upper part of the pyloric mucosa, and around the neck region, clusters of small round cells were seen. The signet ring cell carcinoma appeared to arise from the proliferTakanori HATTORI DEPARTMENT OF PATHOLOGY, SHIGA UNIVERSITY OF MEDICAL SCIENCE, SETA, OHTSU, JAPAN Address correspondence to: Takanori HATTORI, M.D., Ph.D. Department of Pathology, Shiga University of Medical Science, Seta, Ohtsu, 520-2192 Japan The manuscript was received: 15. 02. 2004. Provisionaly accepted: 15.03.2004. Accepted for publication: 23.03.2004. Review article UDC: 616.33-006:616-091.8