粘膜内進展範囲診断の困難な胃癌の病理学的特徴

The Histopathologic Feature of the Gastric Cancer with Difficulty of Determining Lateral Extension

要旨●粘膜内進展範囲診断の困難な胃癌の病理学的特徴について，ESD切除による水平断端陽性早期胃癌症例の病理学的解析を加えて解説した．粘膜内進展範囲診断の困難な胃癌は，表面性状の変化が乏しい癌と周囲粘膜と高低差のない癌に大別できる．表面性状の変化が乏しい癌の原因としては，低異型度分化型腺癌と非全層性発育型癌および背景粘膜の胃炎性変化が挙げられる．周囲粘膜と高低差のない癌は随伴IIb癌を伴う癌であり，IIb癌を構成する癌組織型はNT-porsig型，LS-tub2型，LG-tub1型の3群に分類できる．背景粘膜の胃炎性変化も，周囲粘膜と高低差のない癌の原因となりえる．ESDによって切除された早期胃癌820病変のうち，粘膜層の水平断端が陽性であった病変（HM1病変）は25病変（3.0％）であった．HM1病変は全病変が随伴IIb病変を有しており，随伴IIb病変部において水平断端が陽性となっていた．水平断端陽性部（随伴IIb病変部）の組織所見では，NT-porsig型（12％），LS-tub2型（28％），LG-tub1型（60％）であり，非全層性発育が84％と大多数を占めた．主病変部の癌組織型と随伴IIb癌の組織分類の型はよく相関しており，主病変部の癌組織型から，合併する頻度の高い随伴IIb癌組織分類の型を類推可能である．

　The pathological characteristics of gastric cancer in which intramucosal progression is difficult to measure are discussed along with a pathological analysis of horizontal stump-positive cases of early gastric cancer resected using endoscopic mucosal dissection（ESD）. Gastric cancer for which intramucosal progression extent is difficult to measure can be broadly classified into cancer with few changes in surface properties and cancer with no height difference from the surrounding mucosa. Cancer with few changes in surface properties can be due to poorly differentiated adenocarcinoma, partial-thickness spreading carcinoma, and changes in the background of the gastric mucosa. ［Remark 1］Cancer with no height difference from the surrounding mucosa is accompanied by a type IIb cancer, whose cancer tissue type can be classified into NT-porsig type, LS-tub2 type, and LG-tub1 type. Background changes in the gastric mucosa can also be a cause of cancer with no height difference from the surrounding mucosa.

　Of the 820 early gastric cancer lesions resected using ESD, the horizontal stump of the mucosal layer was positive in 25 lesions（3.1%, HM1 lesions）. All HM1 lesions were accompanied by the type IIb lesions in which the horizontal stump was positive. In addition, tissue findings in the positive part of the horizontal stump（the accompanying type IIb lesion）demonstrated NT-porsig（12%）, LS-tub2（28%）, and LG-tub1（60%）types ; the partial-thickness spreading type accounted for the majority（84%）. The cancer tissue type of the main lesion and tissue classification type of the accompanying type IIb cancer correlated well, suggesting that the tissue type of the accompanying type IIb cancer, which is very frequently complicated, can be inferred from the tissue type of the main lesion.