TSA由来の早期大腸癌の1例

Early Colorectal Cancer Arising from Traditional Serrated Adenoma, Report of a Case

要旨●TSA由来の早期大腸癌の症例を報告する．患者は70歳代，男性．スクリーニング目的の大腸内視鏡検査で，直腸S状部に松毬様の周囲と同色調で一部発赤調を呈する12mm大の0-Ip型病変を認めた．拡大内視鏡では，IV型pit patternの中に通常の腺腫とは異なるV_I型軽度不整pit patternを認め，EMRを施行した．病理組織学的にはTSAの中に粘膜内に限局する高分化管状腺癌を認めた．また，病変基部にmicrovesicular typeの過形成性ポリープを認めた．免疫組織化学的には，TSA部，癌部ともにMUC2陽性，MUC6陰性，CD10陰性，TSA部はMUC5AC陰性で腸型粘液形質を示したが，癌部はMUC5AC陽性の胃腸混合型粘液形質を示した．また，癌部でβ-catenin核内発現とp53蛋白発現の完全消失を示した．遺伝子解析ではBRAF変異陽性，MSSを認めた．

　We report on a case of a man in his 70s with TSA（traditional serrated adenoma）-derived early colorectal cancer. Colonoscopy for screening revealed a 0-Ip type lesion with color similar to the surrounding area and partially reddish, measuring 12mm in diameter, in the rectosigmoid colon. Magnifying endoscopy showed a type V_I-mild pit pattern with an irregular structure different from that of normal adenoma within a type IV pit pattern showing a villous structure. We suspected intramucosal cancer and performed endoscopic mucosal resection. The pathological diagnosis was well-differentiated tubular adenocarcinoma in TSA localized in the mucosa, and a microvesicular type hyperplastic polyp was found at the base of the lesion. Immunohistologically, MUC2 was positive, MUC6 was negative, and CD10 was negative. MUC5AC was negative in the TSA area, indicating a large-intestinal type of mucin phenotype ; MUC5AC was positive in the cancerous area, indicating an intestinal and gastric mixed type of mucin phenotype. In addition, β-catenin nuclear expression was found and p53 protein expression were completely lost in the cancerous area. Genetic analysis showed BRAF mutation and microsatellite stability. Therefore, this case was diagnosed as early-stage cancer via traditional serrated pathway with BRAF mutation.