IIc陥凹型癌（Tis癌）—陥凹を呈した5mm大の粘膜内癌の1例

A Case of 5mm Intramucosal Carcinoma Presenting as a Depressed Lesion

要旨●患者は50歳代，男性．スクリーニング大腸内視鏡検査でS状結腸に5mm大の面状陥凹を呈する発赤調病変を認めた．NBI併用拡大観察でJNET分類Type 2B，クリスタルバイオレット染色下拡大観察でIIIS型pitを認め，cTisと診断した．粘膜下局注併用浸水下内視鏡的粘膜切除術（UIEMR）により一括切除した．病理組織学的には粘膜内に限局する低異型度高分化管状腺癌で，脈管侵襲や切除断端は陰性であり治癒切除と判断した．陥凹型大腸腫瘍は頻度は低いが見逃されやすい病変であり，また腫瘍径が小さい段階で粘膜下層に浸潤する傾向があり，本症例は微小陥凹型粘膜内癌の診断と早期治療の重要性を示す症例と考え報告する．

　A 50s man underwent a screening colonoscopy, revealing a colorectal tumor. A 5mm, reddish, depressed lesion was located in the sigmoid colon. Magnifying narrow-band imaging revealed a type 2B lesion according to the Japan Narrow-Band Imaging Expert Team classification. Magnifying chromoendoscopy with crystal violet staining showed a Kudo type IIIS pit. Based on these findings, the lesion was diagnosed as cTis. Underwater injection endoscopic mucosal resection was performed for this lesion, and en bloc resection was achieved. Histopathologic examination revealed an intramucosal, well-differentiated tubular adenocarcinoma without lymphovascular invasion, and curative resection was achieved. Depressed colorectal tumors are uncommon but easily missed, and even small lesions tend to invade the submucosa. Our findings highlight the importance of accurate diagnosis and early treatment of minimally depressed intramucosal carcinoma.