低異型度分化型胃癌の内視鏡診断―通常内視鏡の立場から

Endoscopic Diagnosis of Low-Grade Atypia and Differentiated Early Gastric Cancer

要旨　ESDを施行した分化型早期胃癌519病変（M癌470病変，SM癌49病変），胃腺腫63病変を対象として，分化型腺癌の異型度の差による内視鏡像の特徴を検討した．分化型胃癌の中で，低異型度癌の占める割合は36.0％であり，低異型度癌は高異型度癌と比較して，粘膜下層浸潤を来した症例は少なく，低分化腺癌への予兆としてもとらえられ，いわゆる手つなぎ型・横這い型の腺管を有する癌を1.6％に認めた．また，低異型度癌では術前の生検で腺腫と診断されていた病変が36.9％も含まれていた．低異型度癌の内視鏡所見は，背景胃粘膜には中等度（C-3，O-1）以上の萎縮を認め，病変は腺境界の肛側に位置する傾向が強かった．また，低異型度癌では正色調から褪色した病変を69.0％と高異型度癌の50.0％に比較して多く認めた．病変の光沢感に関しては，異型度に関係なく75％前後の症例で欠如していた．病変の表面性状として，低異型度癌では胃小区の明瞭化した病変を32.6％，粗大化した病変を40.6％に認め，高異型度癌の各々22.6％，24.7％に比較して高頻度に胃小区の明瞭化および粗大化が認められた．低異型度分化型胃癌は内視鏡治療の適応となることが多く，低異型度癌の内視鏡的特徴を理解しつつ，病変の範囲診断や深達度診断などの慎重な術前診断が必要と考えられた．

　In this study, we investigated 519 lesions of differentiated early gastric cancer（470 intramucosal cancer lesions,49 submucosally invasive cancer lesions）and 63 gastric adenoma lesions after endoscopic submucosal dissection（ESD）, and made clear the characteristics of endoscopic images based on atypia grades of differentiated carcinoma. Among differentiated gastric cancers, low-grade atypia cancer occupied 36.0％ of the total ratio. Lower numbers of low-grade atypia cancer invaded the submucosa as compared to the numbers of high-grade atypia cancer. Laterally spreading cancer, the numbers precursor of poorly differentiated carcinoma, occupied 1.6％. Also, included were 36.9％ of low-grade atypia cancers which were diagnosed as adenoma by biopsy before surgery.

　In endoscopic findings of low-grade atypia cancers, moderate（C-3, O-1）or severe atrophy was observed in the background gastric mucosa, and lesions tended to be located more frequently at the anal side of the gland border. Also, a higher frequency of discoloration from the normal color of lesions（69.0％）was seen in low-grade atypia cancer compared to the frequency in high-grade cancer（50.0％）. Grades of lesions were lost in around 75％ of cases regardless of grades of atypia. Regarding the surface texture of lesions, clarity and coarsening of lesions in the gastric area were more frequently observed in low-grade atypia cancer（32.6％ and 40.6％）compared to high-grade cancer（22.6％ and 24.7％）.

　Endoscopic treatment is often indicated for diffentiated gastric cancer with low-grade atypia. Therefore, careful diagnosis before therapy much as diagnosis of range and invasion depth is important along with an understanding of the endoscopic features of low-grade cancer.