4年間の経過で増大し，潰瘍形成を伴った胃gastrointestinal stromal tumor（GIST）の1例

Gastrointestinal Stromal Tumor (GIST) of the Stomach with an Increase in Size during the 4-Year Period of Observation, Report of a Case

要旨　症例は60歳男性．2001年1月，近医で胃穹窿部後壁の1.5cm大の粘膜下腫瘍を指摘され，経過観察を勧められたがその後の通院はなかった．2005年1月，貧血を来し当科に紹介入院となった．X線・内視鏡検査では頂部に潰瘍を伴う平滑な隆起がみられた．超音波内視鏡検査では，第4層と連続し内部がやや不均一な低エコー性腫瘤として描出され，長径は4cmであった．腹腔鏡補助下胃部分切除を施行したところ，病変は割面が灰白色を呈する充実性腫瘤で，錯綜する紡錘形細胞より構成されていた．免疫染色ではc-kitとCD34に陽性，α-SMAとS-100に陰性，核分裂像4/50HPF，Ki-67標識率は4.6％であった．以上よりlow risk gradeのgastrointestinal stromal tumorと診断した．

　A 60-year-old male was referred to our institution, because of GI bleeding from a gastrointestinal stromal tumor of the stomach. He had been diagnosed as having a gastric submucosal tumor, measuring 15 mm in size, 4 years previously. Under EGD, the tumor was observed as a sessile, submucosal tumor with an ulcer on the top of the tumor. EUS showed the tumor to be a hypoechoic mass derived from the proper muscular layer of the gastric wall, measuring 40 mm in size. Since the tumor apparently increased in size during a 4-year-period, it was resected surgically. Microscopically, the tumor was composed of spindle-shaped cells arranged in trabecular bundles, with 4 mitoses per 50 HPF. Immunohistochemically, the tumor cells were positively stained for c-kit and CD34, but they were negative for S-100, α-SMA and desmin. The Ki-67 labelling index was 4.6％. The tumor was finally diagnosed as a GIST of the stomach, with low risk grade, according to the consensus approach at the National Institutes of Health in 2001.