胃型形質の低異型度分化型胃癌の生検診断における問題点

Challenging Histopathological Diagnosis of Low-grade Differentiated-type Gastric Adenocarcinoma with Gastric Phenotype on Biopsy Specimens

要旨●胃癌の中には組織異型度が低く，生検組織診断上，見逃されやすい一群が存在する．胃型形質を呈する低異型度分化型腺癌もその一つであるが，その中で特に腺窩上皮型を主体とした低異型度腺癌について，その生検組織診断の問題点・注意点を症例の提示を通じて考察した．低細胞異型度と非腫瘍性粘膜組織の組織構築に類似した分化を呈することが特徴である．それらの胃癌からの生検組織を非腫瘍性組織と誤認しないためには，病変の概念の理解のうえに腫瘍上皮の軽微な異型を注意深く認識して，深切り標本作製や免疫染色の追加など必要な病理組織学的検索を行うことが重要であるが，さらに，内視鏡所見も含めた総合的な病変の評価を常に考慮することが必須である．

　Biopsy specimens of some gastric adenocarcinomas of a low histological grade are often misdiagnosed. Low-grade adenocarcinoma with a gastric phenotype is a typical example of such gastric adenocarcinomas, especially those with dominant foveolar differentiation. We discuss the challenging points of their biopsy interpretation through the presentation of some informative cases. These tumors are characterized by low-grade cytological atypia and architectural similarity to non-neoplastic mucosal tissues. Therefore, the first step for accurate biopsy interpretation is to recognize subtle differences between such carcinomatous epithelium and non-neoplastic epithelium, followed by additional histopathological analyses such as deep-cut preparations and/or proper immunohistochemistry. In addition, we must refer to endoscopic findings, which may provide hints leading to the correct histopathological interpretation of biopsy specimens taken from low-grade gastric adenocarcinomas.