H. pylori未感染胃に発生した粘液腺への分化を主体とする胃型形質の低異型度分化型胃癌の1例

Differentiated Gastric Cancer with Gastric-type, Low-grade Atypia（Submucosa and Deeper）, Report of a Case

要旨●患者は60歳代，男性．人間ドックの上部消化管内視鏡検査で，胃体下部大彎に18mm大の周囲になだらかな丈の低い隆起を伴った白色調の陥凹性病変を認めた．背景粘膜に萎縮性胃炎の内視鏡所見は認めず，尿素呼気テストと血清H. pylori抗体も陰性であり，H. pylori未感染胃と思われた．生検で粘膜固有層深部から粘膜筋板内に不整な腺管の増生を認める．細胞異型は乏しくGroup 4と診断された．0-IIc＋IIa型胃癌でSM癌であっても粘膜下層浅層までの浸潤と考え，ESDを施行した．病理組織学的所見は，HE染色像では，粘膜固有層深部から浅層に軽度の核異型を伴う腫瘍腺管が水平方向に増生浸潤し，胃底腺や幽門腺との細胞類似性の乏しい高分化管状腺癌であった．病変中央の陥凹部は一部びらんを伴うも，病変全体の表層は非腫瘍性の粘膜上皮で覆われ，癌の露出は認めなかった．一方，粘膜下層へは多巣性の浸潤を認めた．免疫染色像では，MUC6陽性，MUC5ACは一部陽性，MUC2とCD10は陰性で胃型形質を示し，pepsinogen IとH^＋/K^＋-ATPaseは陰性で，腫瘍は胃底腺への分化は示さず，粘液腺への分化と一部で腺窩上皮への分化が示唆された．これらの病理組織学的特徴は，既報とは異なったタイプの胃型形質の分化型胃癌であることを示し，胃癌の細胞分化と腫瘍発生段階のさらなる多様性を示した興味深い症例と思われる．

　The subject was a 67-year-old man whose upper gastrointestinal endoscopy result during a health check-up revealed a white depressed lesion that was 18mm in size with a surrounding undulating longitudinal low protrusion in the lower portion of the greater curvature of the stomach. The background mucosa revealed no endoscopic findings of atrophic gastritis, while urea breath test and serum test results were negative for Helicobacter pylori antibodies ; thus, the stomach was considered to be uninfected by H. pylori. Biopsy revealed an irregular glandular duct growth extending from deep in the lamina propria mucosae to within the muscularis mucosae. Cellular atypia was poor and grade 4. Even if the lesion was diagnosed as 0-IIc＋IIa-type gastric cancer and submucosal cancer, we considered that the invasion was up to the superficial layer of the submucosa ; thus, endoscopic submucosal dissection was performed. Histopathological findings by HE（hematoxylin eosin）staining revealed proliferative invasion of the glandular tumor in the horizontal direction, with mild nuclear atypia extending deep within the lamina propria mucosae to the superficial layer, and a highly differentiated tubular adenocarcinoma with poor cellular similarity to the fundus and pyloric glands. In the depressed portion in the center of the lesion, some ulceration was present ; however, the superficial layer of the lesion was covered by non-neoplastic mucosal epithelium, and the cancer was not exposed. Multifocal infiltration into the submucosa was observed. Immunostaining results were positive for MUC6, partially positive for MUC5AC, and negative for MUC2 and CD10 as well as pepsinogen-I and H^＋/K^＋-ATPase ; there was no tumor differentiation in the fundus gland. However, differentiation in the mucous gland and some differentiation in the crypt epithelium were suggested. Our case of gastric-type differentiated gastric cancer had histopathological characteristics that differed from those present in existing reports. We believe that this is an extremely interesting case demonstrating cellular differentiation of gastric cancer and a high level of diversity in tumor growth stages.