H. pylori未感染上皮性腫瘍の内視鏡的特徴—胃底腺型胃癌

Endoscopic Features of Gastric Adenocarcinoma of Fundic-gland Type

要旨●H. pylori未感染胃癌の一つである胃底腺型胃癌（gastric adenocarcinoma of fundic-gland type）のNBI併用拡大観察を含む内視鏡診断体系について報告した．胃底腺型胃癌は，病理組織学的には胃底腺型腺癌と胃底腺粘膜型腺癌に分類され，今回，自施設で胃底腺型腺癌と診断された55病変を対象に内視鏡的特徴について検討した．白色光観察での内視鏡的特徴は，①SMT様の隆起性病変（60.0%），②褪色調・白色調（76.4%），③拡張した樹枝状の血管（58.2%），④背景粘膜に萎縮性変化なし（87.3%）の4所見で既報とほぼ同様であった．色調と肉眼型では，①白色調・隆起型（40.0%），②白色調・平坦/陥凹型（36.4%），③発赤調・隆起型（20.0%），④発赤調・平坦/陥凹型（3.6%）の4タイプに分類され，多様性があることが判明し，病理組織学的な考察とタイプ別の特徴を見いだした．H. pylori感染状況による比較では，感染状況により肉眼型の頻度に差があることが判明した．NBI併用拡大観察では，肉眼形態にかかわらず，①明瞭なDLなし（100%），②腺開口部の開大（59.6%），③窩間部の開大（90.4%），④irregularityに乏しい微小血管（80.8%）の4所見が高率に観察され，既報とほぼ同様であった．以上より，胃底腺型腺癌の内視鏡診断は，既報の白色光観察とNBI併用拡大観察の特徴を理解する必要がある．基本的にはH. pylori感染状況と色調・肉眼型を加味したうえで，内視鏡所見から表層の腫瘍成分の有無，表層の非腫瘍性粘膜と上皮下の腫瘍との関係性を推測することが，胃底腺粘膜型腺癌との鑑別も含めた胃底腺型腺癌の内視鏡診断につながると考えられた．

　GAFG（gastric adenocarcinoma of fundic-gland type）is a newly-recognized, special type of cancer in the Japanese classification of gastric carcinoma, 15th Edition, 2017. GAFG was also listed as a new gastric neoplasia in the WHO Classification of Tumours, 2019. GAFG is an uncommon variant of gastric adenocarcinoma with distinct clinicopathological and immunohistochemical features and which is not associated with H. pylori infection. The aim of this study was to evaluate endoscopic features of GAFG from 55 lesions. The most frequently observed features when using WLI（white light imaging）were submucosal tumor shape（60.0%）, whitish color（76.4%）, dilated vessels with branch architecture（58.2%）and background mucosa without atrophic change（87.3%）. Macroscopically, GAFG cases were classified into 4 types, as follows：a. whitish protruded type（40.0%）, b. whitish flat/depressed type（36.4%）, c. reddish protruded type（20.0%）, d. reddish flat/depressed type（3.6%）. The most frequently observed features when using ME-NBI（magnifying endoscopy with narrow band imaging）were indistinct demarcation between lesion and surrounding mucosa（100%）, dilatation of crypt opening（59.6%）, dilatation of intervening part between crypts（90.4%）and blood microvessels without distinct irregularity（80.8%）. Recognition of H. pylori infection state and macroscopic type, clarification of tumor exposure on tissue surface and the relationship between surface mucosa and the tumor located beneath the surface mucosa are all necessary for accurate endoscopic diagnosis of GAFG.