胃過形成性ポリープの癌化例

A White Opaque Substance-positive Gastric Hyperplastic Polyp with Dysplasia

要旨●患者は70歳代，女性．胃体下部大彎に過形成性ポリープ（hyperplastic polyp）を指摘され，内視鏡治療目的に当院へ紹介となった．通常観察では同部位に25mm大の白色部分を伴う発赤調の有茎性ポリープ（Y-IV型）を認めた．NBI観察では，通常観察でも認めた白色部分が明瞭化し，WOS（white opaque substance）と診断された．NBI併用拡大観察ではポリープの表面全体にWOSの密度が低く点状・斑状の部分と密度が高く線状・不整形の部分を認めた．生検では通常の胃過形成性ポリープと診断されたが，WOSが陽性である非典型的な胃過形成性ポリープと診断し，polypectomyを施行した．病理所見上，全体は通常の胃過形成性ポリープの所見であったが，表層には腸型形質を伴う低異型度の高分化管状腺癌を散在性に認めた．最終診断はadenocarcinoma in hyperplastic polypであった．WOSは腸型形質の存在を示唆する所見であること，WOSが癌の領域にのみみられたことから，WOSが胃過形成性ポリープにおける腸型形質を伴う腫瘍化の指標となりうる可能性が示唆された．

　To date, the endoscopic findings of gastric HPs（hyperplastic polyps）with dysplasia remain partially defined, and, thus, the clinical significance of these lesions, including their malignant potential, remains unclear. This report aims to describe a case of a WOS（white opaque substance）-positive gastric HP with dysplasia. A 76-year-old female was referred to our hospital for endoscopic resection of a gastric HP. Upper endoscopy revealed a 25-mm whitish and reddish polypoid lesion on the greater curvature in the lower third of the stomach. Conventional and magnifying endoscopy with narrow band imaging diagnosed the whitish part as a WOS. The assessment of the biopsy specimen revealed that the lesion was a typical gastric HP. However, we suspected that the lesion an atypical gastric HP because of its color and the presence of a WOS. Thus, we performed a polypectomy. Histopathologically, diffuse low- to high-grade dysplasia was observed on the surface of the polyp. Accordingly, we performed immunohistochemical staining using a monoclonal antibody specific for adipophilin as a marker of LDs（lipid droplets）. LDs were detected in approximately all neoplastic cells, especially in the surface epithelium of intervening apical parts and were located in the subnuclear cytoplasm of neoplastic cells. Based on endoscopic and histopathological findings, the WOS-positive epithelium suggested dysplasia of the gastrointestinal phenotype, which could absorb lipids. In addition, the presence of a WOS in a gastric HP could be considered an endoscopic finding predictive of the neoplastic transformation of a gastric HP. This report suggests that a WOS-positive gastric HP should be resected endoscopically to assess its neoplastic transformation.

〔World J Gastroenterol　19：4262-4266, 2013〕