自己免疫性胃炎に発生した胃底腺型腺癌の1例

Gastric Adenocarcinoma of the Fundic Gland Type with Autoimmune Gastritis, Report of a Case

要旨●患者は80歳代，女性．近医で心窩部痛の精査目的で施行されたEGDにて胃隆起性病変を指摘され，精査加療目的で当科紹介となった．当科のEGDにより胃底腺領域優位の萎縮性変化があり，胃体中部前壁には5mm程度の粘膜下腫瘍（submucosal tumor ; SMT）様隆起が認められた．血液検査所見では，抗壁細胞抗体陰性，抗内因子抗体陽性，高ガストリン血症，抗H. pylori抗体陰性であり，除菌治療の既往はなく，自己免疫性胃炎（autoimmune gastritis ; AIG）と診断された．SMT様隆起はESDが行われ，病理組織学的検査結果は胃底線型腺癌であった．胃底腺型腺癌は免疫組織化学的にpepsinogen IやH^＋/K^＋-ATPaseが陽性になるとされるが，本病変は背景粘膜のAIGを模倣するようにH^＋/K^＋-ATPaseが陰性であった．また，chromogranin Aが陽性であり内分泌細胞への分化を伴っていた．これらの免疫組織化学的所見はAIGに発生する胃底腺型腺癌として特異的なものと考えられた．さらに本症例は追加の血液検査により橋本病を合併した自己免疫性多内分泌腺症候群3B型と診断され，甲状腺ホルモンの内服が開始された．

　A woman in her 80s underwent esophagogastroduodenoscopy（EGD）at a previous medical clinic for further evaluation of epigastric pain, which revealed a gastric protruding lesion was identified for which was referred to our department for further evaluation and treatment. EGD performed in our department revealed atrophic changes predominantly in the gastric fundic gland area, and a submucosal tumor（SMT）-like protrusion measuring approximately 5mm was identified on the anterior wall of the gastric body's middle portion. The patient tested negative for anti-parietal cell antibodies and anti-H. pylori antibodies and tested positive for anti-intrinsic factor antibodies. She also had hypergastrinemia. With no history of eradication therapy, the patient was diagnosed with autoimmune gastritis（AIG）. Endoscopic submucosal dissection（ESD）was performed on the SMT-like elevation, and histopathological examination confirmed the diagnosis of fundic gland-type adenocarcinoma. On immunohistochemistry fundic gland-type gastric adenocarcinoma typically tests positive for pepsinogen I and H＋/K＋- ATPase ; however, in this case, it tested negative for H＋/K＋- ATPase, mimicking the background mucosa of AIG. In addition, the Chromogranin A test was positive, indicating differentiation into endocrine cells. These immunohistochemical findings were specific for gastric adenocarcinoma of fundic gland type arising from autoimmune gastritis. Additionally, in this case, further blood tests revealed Hashimoto's thyroiditis, leading to a diagnosis of autoimmune polyendocrine syndrome type 3B, and thyroid hormone replacement therapy was initiated.