1.Overview Smooth muscle sarcoma is a malignant mesenchymal tissue tumor originating from smooth muscle of intestinal wall, vascular smooth muscle of intestinal wall or mucosal muscle of intestinal wall, accounting for 5%-10% of all soft tissue tumors. It is most common in the rectum, accounting for approximately 85% of smooth muscle sarcomas of the large intestine. Retroperitoneal smooth muscle sarcoma is a kind of primary retroperitoneal tumor, accounting for 11% of retroperitoneal malignant tumors, while smooth muscle sarcoma of limbs and soft tissues of thoracic and abdominal walls is relatively rare. Smooth muscle tumors are difficult to distinguish between benign and malignant, mainly because the histological morphology is sometimes not consistent with the biological behavior, often appearing as benign morphology but malignant biological behavior. In addition to local infiltration of smooth muscle sarcoma into adjacent organs and tissues, hematogenous dissemination is the most important way. The etiology of smooth muscle sarcoma is unknown. Some scholars found that there is often loss of chromosome 13q14 and q21 during the course of smooth muscle sarcoma. 3. It can also occur in young people and is rare in children. 70% of cases have an abdominal mass as the first symptom. It can occur in retroperitoneal and peripheral soft tissues. The retroperitoneal region is the most common site of presentation, with larger tumors, mainly in women. Tumors in the peripheral soft tissues and large blood vessels are more common in men. Smooth muscle sarcoma of soft tissue often presents as a mass. Smooth muscle sarcoma of the retroperitoneum of the upper abdomen compressing the upper gastrointestinal tract can cause upper abdominal fullness and discomfort, and the feeling of fullness can increase after eating, and in severe cases, obstructive symptoms can occur. Smooth muscle sarcoma of the extremities and soft tissues of the chest and abdominal wall can be manifested as surface or deep tissue occupancy with rapid growth, and some patients can have pain and other symptoms. The tumor grows rapidly, but the clinical symptoms caused by the tumor occur late, and most of them are already in advanced stage when diagnosed. The advanced tumor can have distant metastasis and systemic toxemia symptoms, such as cachexia, anemia and hypothermia. 4.Examination methods CT is the most important examination means, MRI can be used as a supplementary examination for difficult cases. Tumor excisional examination or CT-guided fine-needle aspiration biopsy can provide the basis for pathological histological diagnosis. Treatment and prognosis The treatment of this primary retroperitoneal smooth muscle sarcoma is based on surgical resection. Important vascular involvement is a common reason limiting complete resection of the tumor, and there is still a recurrence rate of 40%-82% after resection. Most patients have a poor prognosis. The prognosis for soft tissue smooth muscle sarcoma of the extremities and thoracic and abdominal walls is better than that of the abdominal cavity, and treatment is mainly based on surgical enlargement or radical resection. The US NCCN guidelines for the treatment of soft tissue sarcoma recommend surgery + radiotherapy as the primary treatment, with chemotherapy as a complementary treatment.