粘膜下腫瘍の形態を示した胃癌の内視鏡診断―典型症例の検討を中心に

Endoscopic Diagnosis of the Gastric Cancer Showing the Features of a Submucosal Tumor

要旨　1985年から1994年の10年間に当センターで内視鏡的粘膜切除術あるいは外科手術が施行された胃癌（2,786例）のうち，病変の辺縁が“粘膜下腫瘍様”と形容された胃癌16例を検討した．そのうち，癌の粘膜内露出部分が10％以内であるような粘膜下腫瘍の形態を示す胃癌は3例のみであり，内視鏡的に腫瘍全体の形態が粘膜下腫瘍と言えるものは，1989年9月に本誌においてわれわれが報告した1例¹⁾のみであった．したがって，今回の主題のような胃癌が極めてまれであることが確認された．粘膜下腫瘍様とされる胃癌の多くは，粘膜下層以下での癌組織形態が未分化型癌を呈しており（68.8％），粘膜下層以下における組織形態が粘膜下腫瘍様と診断されるうえで重要と考えられた．更に，粘膜下腫瘍様形態を呈するとされる表面型起源広基性大腸sm癌との比較から，粘膜下腫瘍様形態を呈するうえで，癌の発生早期に粘膜筋板を破る必要があり，そのためには，深部浸潤傾向の強い癌が粘膜筋板の薄い箇所に発生する必要があると考えられた．

　Using endoscopy, we studied from 1985 to 1994, 16 cases of gastric cancers which were diagnosed as showing the features of Submucosal tumors (SMT) at their margins. In those cases, there were only three cases in which the area of the cancer in the mucosa was within 10% of the area in the submucosa. There was only one case which showed the typical features of a SMT. A report of this case was published in this journal in 1989. This present study confirmed that typical features, of SMT are rarely found in gastric cancers. In such gastric cancers as were diagnosed as showing features of a SMT, the cancer in the submucosal layer was most commonly undifferentiated adenocarcinoma (68.8%), so we regard it as important to diagnose the structures found by endoscopy in the submucosal layer as tumors like SMT. Moveover, we have compared such gastric cancers with sessile colon cancer invading the submucosa. Nagasako thinks that much sessile colon cancer originates as a superficial lesion. It also shows the features of a submucosal tumor. This comparison leads us to think that if gastric cancer develops showing the features of a SMT, it must have an intense inclination to invade to deep layers and to exist on the thin part of the muscularis mucosa, and which it destroys in the very early phase of its growth.