生検により形態変化を来した直腸gastrointestinal stromal tumor（GIST）の1例

Gastrointestinal Stromal Tumor (GIST) of the Rectum with Remarkable Morphological Change after Endoscopic Biopsy, Report of a Case

要旨　症例は60歳，男性．便柱細小と排便後出血を主訴に受診した．大腸内視鏡検査で直腸Rb前壁に潰瘍を有さない4cm大の粘膜下腫瘍を認めた．生検で採取されたのは健常粘膜のみであった．2週間後の再検時には頂部に広い潰瘍形成を認め，腫瘍の縮小を認めた．潰瘍深部からの生検でGISTと診断できた．2か月後手術直前の再検査でさらに潰瘍の消失と腫瘍の変形，縮小を認めた．腹会陰式直腸切断術が施行され，35mm大で細胞分裂像を伴わないc-kit陽性の紡錘形細胞腫瘍を確認し，低リスクGISTと最終診断した．分葉構造の間隙部や周辺に出血を伴っており，生検による粘膜損傷，糞便による物理的影響，腫瘍内出血，壊死などが形態変化の原因として推察された．

　A 60-year-old male visited our hospital complaining of fecal caliber change and hematochezia. By colonoscopy, a smooth surfaced submucosal tumor was observed in the lower rectum. Biopsy was performed but only normal mucosa was sampled. Two weeks later, colonoscopy was repeated revealing the formation of a large ulcer on the top of the tumor and diminution of tumor size. This time, a biopsy forceps was inserted deeply into the ulceration and spindle shaped cells with features of GIST were obtained. Colonoscopy reexamined before surgery, two months after the first examination, showed healing of the ulceration, deep fissure formation and further diminution of tumor size. Rectal amputation was performed. The tumor was 35 mm in diameter, and was composed of c-kit positive spindle cells in which mitoses were not observed. The diagnosis of GIST of low risk was made. Hemorrhagic spots were observed between and around the lobular structures. The morphological change observed in this case is suspected to have been caused by the procedures of biopsy and the presence of feces, leading to intratumor hemorrhage and necrosis.