多彩な内視鏡像・組織像を呈した胃型形質を示す胃上皮性腫瘍の1例

A Low-grade Neoplastic Lesion of Gastric Type with Diverse Morphology Identified in the Absence of Helicobacter pylori in the Stomach, Report of a Case

要旨●患者は50歳代，男性．検診時の胃透視異常に対して施行した上部消化管内視鏡検査（EGD）にて，胃穹窿部大彎に2.5cm大の褪色調，丈の高い隆起性病変を認めた．拡大観察では乳頭状構造，管状構造など部位により異なる表面微細構造を呈していた．背景胃の粘膜萎縮はなくH. pylori（Helicobacter pylori）未感染胃に発生した胃型腫瘍と考え，内視鏡的粘膜下層剝離術（ESD）を施行した．病理組織像では幽門腺に類似した腫瘍細胞が増生しており，一部に腺窩上皮に類似した乳頭状構造を呈する領域が混在していた．免疫組織化学染色では粘液形質はいずれの領域も胃型で，Ki-67，p53陽性細胞は少数であった．領域ごとに多彩な細胞・腺管構造の異型を示す胃型腫瘍を経験したので報告する．

　A man in his 50s was referred to our hospital for further examination of a gastric lesion. The patient tested negative for Helicobacter pylori, and no atrophic gastritis was detected. Upon endoscopic examination, a distinctive elevated whitish lesion（a nodule-aggregating lesion）measuring 2.5cm was detected in the fundus of the stomach. Biopsy specimens taken from the lesion indicated gastric-type adenoma. Endoscopic findings suggested that the lesion was an adenoma or adenocarcinoma of the gastric phenotype arising from a Helicobacter pylori-negative stomach ; therefore, endoscopic submucosal dissection was performed. Histologically, the tumor mainly comprised the gastric glands with low-grade atypia. Immunohistochemical staining revealed diffuse MUC5AC expression in the upper layer and diffuse MUC6 expression in the middle-to-lower layer. CDX2 and MUC2 were not expressed. The tumor exhibited atypical cellular and ductal structures in various regions. The entire lesion was identified as a low-grade, neoplastic gastric-type lesion.