粘膜下腫瘍様の形態を示した胃体部超高分化型腺癌の1例

Extremely Well Differentiated Adenocarcinoma of the Stomach Mimicking a Submucosal Tumor, Report of a Case

要旨　症例は50歳，男性．胃集検で異常を指摘され精査のため当科紹介となった．胃X線検査，内視鏡検査では胃角部前壁に5cm大でbridging fold様の皺襞集中を伴う粘膜下腫瘍（SMT）様隆起を認めた．胃壁の伸展性は比較的良好であり腫瘍表面には不整形の陥凹を認めたが，正常粘膜類似の発赤した陥凹面であり典型的な2型癌とは異なっていた．超音波内視鏡検査で腫瘍は粘膜下に主座を置く低エコー像を呈し漿膜浸潤が疑われた．数回の生検においても上皮腺管の異型度からは癌の診断が困難であったが，臨床的に2型進行癌と診断し幽門側胃切除術を施行した．病理組織学的には腫瘍表層部は超高分化型腺癌で深部浸潤に伴い低分化傾向を示す深達度ssの進行癌であった．粘液形質は中央の陥凹部は完全小腸型，周囲は胃型の形質が主体である胃型と腸型の混合型であった．

　A 50-year-old man visited our unit without any felt complaint, because of the abnormality of the barium meal study at a mass screening in November, 2002. X-ray examination showed a tumor, measuring 5cm in size, with submucosal growth at the anterior wall of the lower body. Additionally, a double-contrast view revealed converging folds and an irregular depression on the surface of the tumor. Endoscopic findings of the same area showed the tumor mimicking a submucosal tumor with fold convergence and irregular depression. The surface of the irregular depression was covered with normal-looking mucosa without white coating. Endoscopic ultrasonography revealed a hypo-echoic tumor presenting mainly in the 3rd layer, with thickening of the 4th layer and irregularity of the 5th layer. Histological findings of the biopsy specimens could not prove a cancer, but, from the clinical standpoint, we considered the tumor to be an advanced cancer. The patient underwent distal gastrectomy in January, 2003. Pathological findings indicated that the tumor consisted of extremely well differentiated adenocarcinoma with invasion out of the serosa. By immunohistochemical stain using antibodies for human gastric mucin, MUC 2 and CD 10, the tumor's phenotype was classified as combined type, because characteristics of gastric phenotype were seen at the periphery and lower sides of the tumor, while that of complete intestinal type was seen in the depressed area at the center.

　1) Department of Gastroenterology, Asahikawa Kosei General Hospital, Asahikawa, Japan