早期胃癌の背景としての胃粘膜―内視鏡的立場より

Gastric Mucosa: An endoscopic study of mucosal changes in the presence of early gastric cancer

　胃癌が胃粘膜のある種の変化（状態）をその発生母地とするなら，早期胃癌の存在する胃粘膜には何か特徴がみられるのではなかろうか．いま一歩話を進めて，胃癌が慢性胃炎，胃潰瘍，ポリープなどをその発生母地とするなら，胃癌，特に早期癌の非癌部胃粘膜は，慢性胃炎，胃潰瘍，ポリープを単独に有し，なおかつ発癌に到らない胃の粘膜とは何か本質的な相違があるのではないか，そしてまた，その変化は内視鏡的なlevelで識別可能なものであろうか，と言う疑問がある．しかし日常，胃X線あるいは内視鏡を武器として早期胃癌の診断をしている臨床医にとって，この疑問はある意味ではナンセンスであり，明確な解答の得られる可能性の少ないもののように思える．

　すなわち，ある病変の鑑別診断をする場合，重要なのは通常その病変自身の持つ性質であり，その背景の胃粘膜像ではないと考えられる．例えば，潰瘍性病変が良性であるか，悪性であるか迷うことはしばしばあるが，病変の周辺粘膜が良・悪性の鑑別診断の根拠となることは，絶無ではないにしろ極めて稀であると考えられる．しかし，前述の疑問は依然として臨床医の頭の中にあり，明確でないにしても，やはり一つの結論を出しておく必要があるように思う．それでは早期癌の非癌部胃粘膜には内視鏡的に何か特徴があるのだろうか，それは早期癌の型によって異なるのか，あるいは組織型によるのか，そしてまた，良性疾患である胃潰瘍，ポリープのそれと異なるのであろうか，また進行癌と早期癌ではどうであろうかなど，これらの点に関して本院の早期癌症例をもとにし非癌部胃粘膜像を主に慢性胃炎の面から論じてみよう．

　Two hundred and ten cases (210) of early gastric cancer were examined endoscopically to assess mucosal changes in non-cancerous mucosa. Our control groups consisted of patients with gastric polyps, gastric ulcers and advanced gastric cancers. Gastric mucosal changes were observed in two standard areas, the area of pyloric glands 〔P〕, and the area of fundic glands 〔F〕. The endoscopic diagnoses of the mucosa were classified as follows: normal, superficial gastritis, hypertrophic gastritis and atrophic gastritis. Early gastric cancer was classified into three types. An elevated type 〔Ⅰ, Ⅱa〕, a mixed type 〔Ⅱa+Ⅱc, Ⅱc+Ⅱa〕 and a depressed type 〔Ⅱc, Ⅱc+Ⅲ, Ⅲ+Ⅱc〕.

　Mucosal changes of atrophic gastritis in the 〔F〕 area were present in 82.6％ of these cases of gastric cancer with the elevated lesion, and in 76.4％ of these cases of gastric cancer with the depressed type. The association of atrophic gastritis with the two histological types of gastric cancer was studied. Cases with differentiated carcinoma showed atrophic changes in the uninvolved mucosa in 82.1％ of cases, whereas the group with undifferentiated carcinoma had atrophic changes in only 65.7％ of cases.

　Atrophic changes were observed in the mucosa in 84.9％ of cases of gastric polyp and 66.3％ of gastric ulcer cases. The incidence of atrophic gastritis in cases with gastric polyps was similar to that in cases with the elevated type of early gastric cancer. Gastric ulcer was associated with an incidence of atrophic gastritis very similar to that found in association with the depressed type of early gastric cancer.

　Intestinal metaplasia suspected endoscopically was observed in the uninvolved mucosa of 6.9％ of cases with elevated type early gastric cancer, 5.4％ of cases associated with the depressed type of early gastric cancer, 10.5％ of cases associated with differentiated and 6.9％ of cases with undifferentiated early gastric cancer. Atrophic gastritis was seen more commonly in association with the elevated and differentiated types of early gastric cancer rather than the depressed and undifferentiated types. Intestinal metaplasia was observed predominantly in association with cases of the elevated and differentiated types of early gastric cancer.

　These findings, resulting from the endoscopic observation of changes in the non-cancerous mucosa, suggest that differentiated carcinoma arises in areas of intestinal metaplasia whereas undifferentiated carcinoma arises in the gastric glands.