Serrated polyposis syndromeに合併した上行結腸T1癌の1例

A Case of T1 Colon Cancer in the Ascending Colon Arising from Serrated Polyposis Syndrome

要旨●患者は60歳代，男性．便潜血検査精査のため近医で大腸内視鏡検査を施行したところ，多発性大腸ポリープおよび上行結腸に隆起性病変が認められ，当院へ紹介された．当院での大腸内視鏡検査にて，上行結腸に径15mmの0-IIa＋IIc型病変を認め，精査の結果，T1b鋸歯状腺癌と診断された．同腫瘍以外にも，径10mmの鋸歯状腫瘍が多数認められ，WHO分類 第5版の基準を満たしていたため，鋸歯状ポリポーシス症候群（serrated polyposis syndrome ; SPS）と診断された．CT検査では明らかなリンパ節および他臓器への転移は認められなかったため，ロボット支援下にて結腸右半切除術（D2郭清）を施行した．病理組織学的には，病変はwell to moderately differentiated tubular adenocarcinoma（tub2>tub1）であり，pT1b（SM 1,600μm），INFb，Ly0，V0，Pn0，BD1と診断された．また，MSI検査では，MSI-highであり，RAS/BRAF変異解析ではBRAF V600E変異陽性が認められた，鋸歯状腺癌であった．

　The patient was a man in his 60s who underwent a colonoscopy at a nearby clinic for further evaluation of a positive fecal occult blood test, which revealed multiple colonic polyps and a raised lesion in the ascending colon. He was referred to our hospital for further investigation, where another colonoscopy identified a 15-mm 0−IIa＋IIc lesion in his ascending colon, and a detailed examination led to the diagnosis of T1b serrated adenocarcinoma. In addition to this lesion, multiple serrated lesions measuring approximately 10mm were also observed, fulfilling the WHO criteria for Serrated Polyposis Syndrome. CT imaging revealed no evident lymph node or distant organ metastasis, and robot-assisted right hemicolectomy with D2 lymph node dissection was performed. Histopathologically, the lesion was also identified as moderately differentiated tubular adenocarcinoma（tub2>tub1）, pT1b（SM 1600μm）, INFb, Ly0, V0, Pn0, BD1. This tumor was a serrated adenocarcinoma that tested MSI-high in the MSI analysis and also tested positive for the BRAF V600E mutation during the RAS/BRAF mutation analysis.