本文报告3例罕见的原发于胃肠道的平滑肌肉瘤（leiomyosarcoma，LMS）病例。3例患者中，男性1例，女性2例，年龄为58~68岁；肿瘤原发于胃2例，小肠1例。患者的手术切除标本，在光学显微镜下可见，肿瘤呈浸润性生长，均侵犯固有肌层，2例表面黏膜有溃疡；肿瘤细胞呈梭形，可见束状、交织状排列，细胞质丰富、嗜酸，细胞核呈中-高度异型，核分裂象易见（50~100个/50 HPF）。免疫组化染色显示，肿瘤细胞3例Desmin阳性，2例SMA、Caldesmon阳性，3例均为CD117、Dog-1、CD34阴性，Ki-67增殖指数30%~80%。3例患者随访了11~53个月，其中2例患者无瘤生存，1例患者于手术后30个月发生肿瘤胰腺转移，随访至今53个月，仍生存。LMS是一种少见的软组织肉瘤，原发于胃肠道的LMS极为罕见。该病确诊依据是术后病理检查，LMS肿瘤细胞呈梭形，细胞质嗜酸，细胞核异型明显，表达平滑肌细胞标志物，需与胃肠道间质瘤及其他梭形细胞肿瘤相鉴别。LMS以手术治疗为主，患者的预后较差，故正确诊断该病至关重要。

This study reports three rare cases of primary leiomyosarcoma (LMS) originating in the gastrointestinal tract. Among the three patients, one was male and two were females, aged 58 to 68 years. The tumors originated in the stomach in two cases and in the small intestine in one case. Histopathological examination of the surgical specimens showed that the tumors exhibited infiltrative growth, all invading the muscularis propria, and mucosal surface ulceration was observed in two cases. The tumor cells were spindle-shaped, arranged in bundles or interwoven patterns. The cytoplasm was abundant and eosinophilic, and the nuclei showed moderate to high atypia, with mitotic figures easily observed (50-100/50 HPF). Immunohistochemical staining revealed that the tumor cells were positive for SMA(3/3), Desmin and Caldesmon(2/3), but negative for CD117, Dog-1, and CD34(3/3). The Ki-67 proliferation index ranged from 30% to 80%. The follow-up periods of the three patients ranged from 11 to 53 months. Two patients were tumor-free, while one patient developed pancreatic metastasis 30 months after surgery but remained alive at the last follow-up at 53 months. LMS is a rare soft tissue sarcoma, and primary gastrointestinal LMS is extremely rare. The definitive diagnosis of the disease is based on postoperative pathological examination. LMS tumor cells are spindle-shaped, with eosinophilic cytoplasm and significant nuclear atypia, expressing smooth muscle cell markers. It is necessary to differentiate from gastrointestinal stromal tumors and other spindle cell tumors. Surgical resection remains the primary treatment, but the prognosis is generally poor, highlighting the importance of accurate diagnosis.