sessile serrated adenoma/polypに合併した大腸粘膜下層浸潤癌の1例

Submucosal Invasive Colorectal Cancer with Sessile Serrated Adenoma/Polyp in the Sigmoid Colon, Report of a Case

要旨　患者は72歳，男性．便潜血反応陽性のため施行した下部消化管内視鏡検査にてS状結腸に10mm大の広基性隆起性病変を認めた．病変は丈の高い隆起部と低い部分から成り，丈の低い部分はII型に類似したpitがみられたが，NBIでは網目状の微細血管パターンが観察された．丈の高い隆起部では大小不同な管状pitが密に分布しており，一部では辺縁に不整を伴うpitの混在を認めV_I軽度不整pitに相当した．さらにNBIでも不整な表面模様と微細血管パターンがみられた．腺腫あるいは鋸歯状病変に合併した粘膜内癌と診断し，内視鏡的粘膜切除術を施行した．病理組織所見は丈の高い隆起部に一致して粘膜下層へ浸潤する管状腺癌を認めた．丈の低い部分は鋸歯状腺管から成り，細胞異型は軽度であったが腺底部では腺管密度が増加し，不規則な分岐や拡張を伴う腺管の構造異常を認めたためSSA/P（sessile serrated adenoma/polyp）と診断した．本病変はSSA/Pに合併した粘膜下層浸潤癌と考えられた．

　A 72-year-old man underwent colonoscopy because of positive fecal occult blood. A sessile elevated lesion about 10mm in diameter was seen in the sigmoid colon. Chromoendoscopic view with indigo carmine dye showed a sessile elevated lesion with a shaped demarcation line and two compartments, a slightly elevated lesion and a marked protruded lesion. Magnifying endoscopic views showed regular oval pits in a slightly elevated lesion and irregular tubular pits in a marked protruded lesion. Narrow band imaging view showed regular surface pattern and regular microvessel features in a slightly elevated lesion and irregular surface pattern and irregular microvessel features in a marked protruded lesion. We diagnosed it as a cancer with a serrated lesion and performed endoscopic mucosal resection. Histological examination revealed a well to moderately differentiated type tubular adenocarcinoma with a serrated lesion. Depth of invasion was 2,800μm, and lymphatic vessel and venous invasion were identified by D2-40 immunostain and victoria blue stain, respectively. In the serrated lesion, increased crypt blanching and dilation, and cytological atypia was seen in the lower crypt. Histological diagnosis was submucosal invasive colorectal cancer with sessile serrated adenoma/polyp.