目的　探讨胃肠道间质瘤 (GIST)的起源或分化。方法　采用免疫组织化学EnVision和电镜的方法对GIST进行研究。结果　 2 12例GISTCD117、CD34、α 平滑肌肌动蛋白 (SMA)、肌特异性肌动蛋白、结蛋白阳性率分别为 96 7% ,77 3% ,19 3% ,15 6 % ,1 9% ,其中S 10 0和PGP9 5的阳性反应分别为 16 3%及 12 3%。超微结构显示瘤细胞含丰富的线粒体 ,粗面内质网、游离核糖体和中间丝 ,有的细胞切面可见溶酶体和脂滴 ,高尔基复合体在核周分布 ,质膜处偶尔不规则地分布着一些微饮泡、密斑样结构及不连续的基板。部分病例细胞有多量细长指状突起 ,突起内有胞内成分如线粒体、粗面内质网延续 ,突起之间或突起与细胞膜有连接结构。细胞外间质内可见胶原原纤维或团丝样纤维。结论　GIST免疫表型及超微结构特征与胃肠壁成熟卡哈尔间质细胞相似 ,提示GIST可能是起源于幼稚间充质细胞向卡哈尔间质细胞分化的肿瘤 ,并具有一定的肌性特征 Objective To investigate the origin or differentiation of gastrointestinal stromal tumors (GISTs). Methods Immunohistochemistry EnVision and electron microscopy were used to study GIST. Results The positive rates of GISTCD117, CD34, α smooth muscle actin (SMA), muscle specific actin and desmin were 96 7%, 77 3%, 19 3%, 15 6%, 19% The positive reactions of S 10 0 and PGP 9 5 were 16 3% and 12 3% respectively. The ultrastructure showed that the tumor cells were rich in mitochondria, rough endoplasmic reticulum, free ribosomes and intermediate filaments. Some cell sections showed lysosomes and lipid droplets. The Golgi complex was distributed in the perinuclear and occasionally irregular at the plasma membrane Distributed with a number of micro-bubble, dense-like structure and discontinuous substrate. In some cases, there are a large number of elongated finger-like cells with intracellular components such as mitochondria and rough endoplasmic reticulum in the protuberances, and the connections between protuberances and protuberances and cell membranes. Collagen fibrils or filamentous fibers can be seen in the extracellular matrix. Conclusions The immunophenotypic and ultrastructural features of GIST are similar to mature cardar stromal cells in gastrointestinal wall, suggesting that GIST may be derived from naive mesenchymal cells differentiated into Cajal stromal cells and have certain muscle Sexual characteristics