陥凹型由来と考えられた微小大腸SM浸潤癌の1例

A Minute Submucosal Invasive Colorectal Carcinoma Arising from a Depressed-type Lesion Suggestive of de novo Carcinogenesis

要旨●患者は60歳代，男性．便潜血陽性を契機に下部消化管内視鏡検査を施行したところ，直腸〜S状結腸移行部に6〜7mm大の0-IIc型（表面陥凹型）病変を認めた．NBI非拡大観察で茶褐色調を呈し，NBI拡大観察でJNET分類Type 2B，色素拡大でpit pattern V_I型高度不整を示した．内視鏡的粘膜切除術（EMR）にて一括切除により高〜中分化管状腺癌，SM1（650μm），脈管侵襲陰性，簇出Grade 1，断端陰性と診断され根治切除が得られた．腺腫成分を欠く微小陥凹型T1癌はde novo発癌の関与が示唆され，小病変であっても早期に浸潤能を獲得しうることを示している．陥凹型病変は検出が困難で，高解像度内視鏡やNBI，AI支援診断の併用が重要である．また，治療後のサーベイランスではJapan polyp studyの知見を踏まえたうえで，de novo癌リスクを考慮した戦略が求められる．

　A man in his 60s was referred for a colonoscopy after a positive fecal occult blood test revealed a 6-7mm 0-IIc depressed lesion at his rectosigmoid junction. Non-magnifying NBI demonstrated a brownish discoloration, while magnifying NBI showed a JNET type 2B pattern, and chromoendoscopy revealed an irregular Vi pit pattern. EMR was performed en bloc, and the lesion was identified as well-to-moderately differentiated adenocarcinoma with SM1 invasion（650μm）, without vascular invasion, budding（Grade 1）, or margin involvement, achieving curative resection. The absence of adenomatous components in this small depressed T1 cancer suggests de novo carcinogenesis, indicating that even diminutive lesions can acquire invasive potential at an early stage. Because depressed lesions are difficult to detect, the combined use of high-resolution endoscopy, NBI, and AI-assisted diagnosis may prove instrumental. Furthermore, post-treatment surveillance should incorporate the findings of the Japan Polyp Study and consider strategies tailored to the risk of de novo cancer.