Ⅰs型からⅡc＋Ⅱa型へ形態変化を来した大腸sm癌の自然経過をみた1例

Early Invasive Colon Cancer that Transformed from a Sessile (Is Type) Polyp into a Concave Lesion (IIc＋IIa Type), Report of a Case

要旨　患者は初診時81歳，男性．初回内視鏡検査ではS状結腸に8mm大のくびれを有す隆起性病変(Ⅰs型)を認めた．それから11か月後に施行した内視鏡検査では初回と異なり，病変全体が陥凹を主体としたⅡc＋Ⅱa型の表面陥凹型腫瘍に形態を変えていた．内視鏡的に摘除された病変は直径10mmの病変で，実体顕微鏡観察では陥凹部は不整構造を示し，陥凹型由来とされるsm浸潤癌に一致するものであった．病理組織学的に間質の線維化の強い高分化腺癌で，癌は陥凹部の内側のみに存在し，non-polypoid growth(NPG)の形態を呈していた．本例は生検の既往がなく，Ⅰs型からⅡc＋Ⅱa型へ形態変化を来した早期大腸癌としては最初の報告である．

　A sessile polyp 8 mm in diameter was observed by colonoscopy in the sigmoid colon of an 81-year-old man. The lesion was classified Is type, and no biopsy was undertaken. However, 11 months later, the polyp transformed into a concave lesion (IIc ＋ IIa type), and this was removed by saline-assisted polypectomy. The resected lesion was 10 mm in diameter. Stereomicroscopic examination revealed an irregular surface without an adenomatous pit pattern in the concave area. Histologically, well differentiated adenocarcinoma with marked fibrosis was revealed in the concave area, but no adenoma component was evident, even in the surrounding ridge. The carcinoma had massively invaded the submucosal layer. The initial colonoscopic finding was typical polypoid lesion (Is type). However, the findings at the second colonoscopic examination showed a typical superficial depressed-type lesion (NPG-IIc＋IIa type). This is the first report of an early invasive colorectal cancer that changed from a sessile type to a concave type without biopsy. We think that this case is interesting for considering the natural course of colorectal cancer.