SMT様の形態を呈した大腸浸潤性微小乳頭癌の1例

A Case of Primary Colon Cancer Composed of Invasive Micropapillary Carcinoma Showing Submucosal Tumor-like Appearance

要旨　浸潤性微小乳頭癌（invasive micropapillary carcinoma ; IMPC）の組織像を示す原発性早期大腸癌を経験したので報告する．患者は40歳，男性，自覚症状なし．人間ドックで施行された大腸内視鏡検査にて上行結腸に10mmのSMT様の隆起性病変を指摘された．頂部には陥凹を認め，拡大内視鏡では陥凹部においてSM高度浸潤の所見であった．生検で低分化腺癌と診断され，腹腔鏡補助下右半結腸切除術が施行された．組織学的にはリンパ管様の空隙内に微小乳頭状の癌胞巣が存在する特徴的な像を認めた．免疫染色ではEMA（epithelial membrane antigen）が微小乳頭状癌胞巣の管腔側表面で陽性となり，IMPCに特徴的なinside-out patternを呈した．IMPCは高頻度にリンパ管侵襲・リンパ節転移を来す予後不良な癌腫として注目されているが，本症例は術後1年再発を認めていない．

　A 40-year-old man without any symptom underwent colonoscopy for a medical checkup. A small protruded lesion showing submucosal tumor-like appearance with depressed area on the top of tumor was detected in the ascending colon. The tumor size was 10mm in diameter. Magnifying view suggested the tumor had invaded into the deep submucosal layer in the depressed area. Laparoscopic-assisted right hemicolectomy was performed. Histologically, the tumor was predominantly composed of small papillary tumor cell clusters floating in clear spaces resembling lymphatic channels. Immunohistochemically, epithelial membranous antigen was expressed at the stroma-facing surface of the cells, showing a characteristic“inside-out growth pattern”. Therefore, this tumor was diagnosed as invasive micropapillary carcinoma（IMPC）. IMPCs have been reported to be a poorly prognostic tumor with a high incidence of lymphatic invasion and lymph node metastasis. The patient has enjoyed good health for one year without recurrence.