Superficially serrated adenoma（SuSA）様の鋸歯状病変を由来とし粘膜下層浸潤を呈したS状結腸癌の1例

Sigmoid Colon Carcinoma with Submucosal Invasion Derived from a Superficially Serrated Adenoma-like Serrated Lesion, Report of a Case

要旨●患者は60歳代，女性．便潜血陽性にて当科を受診し，大腸内視鏡検査にてS状結腸に約35mm大の0-IIa＋Is型病変を認めた．辺縁は背景粘膜とほぼ同色調の平坦隆起を呈し，内部は発赤絨毛様構造を呈する隆起部と，硬さを認める結節隆起を伴っていた．NBI併用拡大内視鏡観察では平坦隆起部および発赤隆起部はJNET分類Type 2A，硬さを認める結節隆起部はJNET分類Type 2Bと考えられた．色素内視鏡観察ではそれぞれ伸長したII型様pit，鋸歯状構造を伴うIV型様pit，VI型高度不整と判断した．ESDにて切除を行った．病理組織像では平坦隆起部の深部は管状腺腫様で，表層は鋸歯状変化を伴っていた．Ki-67陽性細胞は陰窩底部〜中層まで分布しており，SuSAの病理組織像として矛盾しないと考えられた．発赤隆起部は鋸歯状変化を伴うTSA，一部管状腺腫様，結節部はtub1相当の腺癌と診断し，粘膜下層へ6,000μmの浸潤を認めた．分子解析ではいずれのコンポーネントもKRAS変異を認め一連の病変と考えられたが，RSPO融合/過剰発現は認めなかった．本症例はSuSA様の鋸歯状病変を由来としてTSA，一部は管状腺腫様に進展し癌化に至った病変と考えられた．

　The patient included in this study, a female in her 60s, visited our hospital with a positive fecal occult blood test. Colonoscopy results revealed the presence of a 0-IIa＋Is lesion with a diameter of approximately 35mm in the sigmoid colon. The lesion had flat margins and the color tone was the same as that of the background mucosa. The interior of the lesion exhibited erythematous villous structures and a hard nodule. Based on the results of magnifying endoscopy with narrow-band imaging, the flat and erythematous areas were diagnosed per the Japan NBI Expert Team（JNET）as JNET Type 2A and the hard nodule was diagnosed as JNET Type 2B. An elongated type II-like pit pattern, a type IV-like pit pattern with a serrated structure, and a VI-severe pit pattern were observed upon chromoendoscopy. This lesion was resected by endoscopic submucosal dissection. Histopathology results revealed the distribution of Ki-67-positive cells from the base of the crypts to the middle layer, thereby confirming the pathology of superficially serrated adenoma（SuSA）. The erythematous area with serrated changes, some of which were tubular adenoma-like, was diagnosed as Traditional serrated adenoma（TSA）, and the nodular area was diagnosed as adenocarcinoma equivalent to well differentiated tubular adenocarcinoma, with 6000μm invasion into the submucosal layer. The presence of Kirsten rat sarcoma virus（KRAS）mutations in both components detected through molecular analysis indicated a series of lesions ; however, no R-spondin（RSPO）fusion/overexpression was detected. This case is unique and has been reported here since a lesion considered to be a serrated lesion originated as a SuSA-like lesion and then developed into a TSA and partly into a tubular adenoma-like lesion that later developed into a carcinoma.