詳細な画像所見と遺伝子解析結果が得られた直腸の腺腫と腺癌の衝突腫瘍の1例

Collision Tumor of Adenoma and Adenocarcinoma in the Rectum Diagnosed Via Genetic Analysis, Barium Enema, and Conventional and Magnifying Endoscopy, Report of a Case

要旨●患者は70歳代，男性．注腸X線造影検査や大腸内視鏡検査では下部直腸に中心に陥凹を伴った丈の低い隆起性病変を認め，病変右側には一段丈の高い小隆起を伴っていた．NBIや色素拡大観察では病変の大部分を占める丈の低い隆起部で血管や構造不整が目立ち腺癌を疑い，病変右側の小隆起部では血管や構造不整が目立たず腺腫を疑った．一部粘膜下層（SM）浅層浸潤の可能性もあったが，全体的に粘膜内病変と診断し内視鏡的粘膜下層剝離術を施行した．病理組織学的には一部でSM浅層浸潤（400μm）を認めたが大部分が粘膜内にとどまる高分化管状腺癌で，右側の小隆起は低異型度管状腺腫であった．境界部では内視鏡的に両者を明瞭に区別することが可能で，また分子生物学的所見でも腺腫成分のみでNRAS，APCの遺伝子変異を認めたことから，腺腫と腺癌の衝突腫瘍と診断した．

　A 70-year-old man underwent colonoscopy for colorectal cancer screening, which revealed a flat-elevated lesion with central depression in the lower rectum and a small protruding lesion in the right side of the flat-elevated lesion. Magnifying narrow-band imaging endoscopy and chromoendoscopy revealed an irregular surface and vessel pattern in the flat-elevated lesion and a regular surface and vessel pattern in the small protruding lesion. The tentative diagnosis was intramucosal or early cancer with slight submucosal invasion. Endoscopic findings of the small protruding lesion suggested tubular adenoma. He was subsequently treated via endoscopic submucosal dissection. Histological examination of the resected specimen showed a well-differentiated adenocarcinoma invading the shallow submucosal layer（invasion depth：400μm）. The small protruding lesion in the right side of the flat-elevated lesion was a tubular adenoma. The horizontal and vertical margins were free of tumor cells. Molecular analysis revealed that the adenoma component was positive for NRAS and APC mutations, whereas the adenocarcinoma component was negative for NRAS and APC mutations. Therefore, he was diagnosed with collision tumor of adenoma and adenocarcinoma.