Soft tissue sarcomas are malignant tumors that occur in connective tissues, including subcutaneous tissues, muscles, tendons, blood vessels, connective tissue spaces, and the stroma of the pillars of cavernous organs. The exceptions are those that occur in bones, reticuloendothelial system, and neuroglia. The cellular origin of soft tissue sarcoma is primitive mesenchymal stem cells, located in the non-segmental mesoderm, so it can grow in different parts of the body. The clinical manifestation of soft tissue sarcoma is a mass, but the mass itself has no function, so it only produces symptoms when the mass increases in size and compresses the surrounding tissues. Classification and treatment of soft tissue sarcoma 1.Fibrosarcoma: fibrosarcoma originates from fibroblasts and is a malignant tumor of fibrous tissues, which is mostly found in children under 5 years old, and some of them are also called “congenital and infantile fibrosarcoma”, and it is slightly more common in boys than girls. Fibrosarcoma can occur in any part of the body, with the lower limbs accounting for about 50% of the cases. It is mainly found in feet, ankles and calves, so it is more common in upper limbs such as hands, wrists and forearms, and it can also be found in trunk, retroperitoneum and parotid glands, oral mucosa, tonsils and mastoids, etc. It is also found in burn scars, retinas and other organs. Burn scar, retinoblastoma, Hodgkin’s lymphoma are easy to grow this tumor after radiotherapy. The tumor is a fast-growing painless mass, which can be doubled in 2~3 weeks, and its boundary is often unclear, and when it presses on nerves such as the common peroneal nerve or its branches, it can produce compression symptoms. There are reports of several distant tumors in the same limb, and X-ray examination shows soft tissue mass or thickening of the cortex of the long bones of the limb, and very rarely, bone destruction may occur. Pulmonary metastases may occur in infantile patients. Treatment should include wide and complete excision of the tumor, including at least 3 cm of tissue around the tumor. Incomplete resection may lead to recurrence, requiring reoperation and consideration of amputation if necessary. Fibrosarcoma has low radiosensitivity, so high-dose radiotherapy (6Gy) has been advocated, especially in multiple recurrences or to avoid amputation. The opinion of chemotherapy is not unanimous, some people advocate according to rhabdomyosarcoma program, used in recurrence and metastatic cases, and some people advocate preoperative radiotherapy and chemotherapy. 2.Malignant fibrous histiocytoma: it is mostly diagnosed as painless mass. The tumor is often large, clear, hard and deep. Regional lymph nodes may be enlarged. When invading adjacent bone, the tumor may be fixed, accompanied by pressure pain. Malignant fibrous histiocytoma, also known as fibrous histiocytosarcoma, fibro-yellow sarcoma, malignant fibro-yellow tumor and so on. It was firstly described by OBrienStout in 1964 and is less common in children. 3.Liposarcoma: a larger and deeper mass found by chance, mostly occurring below the deep fascia of the muscle deep surface or intermuscular fascia near blood vessels and nerves, retroperitoneal septum, flexion side of the main joints of the limbs and the inner side of the thigh. The tumor is poorly defined, hard, substantial, and unremarkable in terms of tenderness. Liposarcoma originates from primitive mesenchymal cells, it is more common in adults and less common in pediatrics, it occurs most often at the age of 10-15 years old, and there is no difference between men and women. Liposarcoma comes from adipose tissue, so it grows in all parts of the body, the most occurs in retroperitoneum, the other is femur and knee, the tumor grows insidiously, slowly, without obvious boundary, no special clinical manifestations. Treatment: complete resection by surgery is the best treatment method, radiotherapy is not precise, chemotherapy is only used when surgery is invalid or cannot be implemented, and commonly used drugs are cyclophosphamide, vincristine, actinomycin D (rehabilitacin), but its effect is not clear. 4.Hemangiosarcoma: the tumor is nodular, painless, purplish red, superficial ones are easy to bleed and break. Clinical manifestations can be divided into 3 types: superficial diffuse type (can be multifocal performance), nodular type and ulcerated type. 5.Smooth muscle sarcoma: smooth muscle sarcoma can occur in any organ or tissue containing smooth muscle, most commonly seen in the gastrointestinal tract. In addition to the gastrointestinal tract, children’s smooth muscle sarcoma mainly occurs in the retroperitoneum, trachea, bronchus and smooth muscle in the lungs. Generally, the prognosis of tumors in the gastrointestinal tract and subcutaneous tissue is better, while the prognosis of retroperitoneal and mesenteric tumors is worse. Smooth muscle sarcomas of the gastrointestinal tract may be distributed in various sites from the stomach to the rectum and may be multifocal. The tumor can lead to intestinal obstruction and intussusception. Physical examination may reveal a palpable mass, and children may present with anemia, abdominal pain, and gastrointestinal bleeding. Gastrointestinal diagnosis can be made by barium meal X-ray imaging, the typical signs are filling defects with neat edges, and there can also be ulcer manifestations. Fiberoptic gastroscopy and enteroscopy are useful in diagnosis. Treatment is complete resection of the tumor, but with a wide range, e.g., the gastrointestinal tract should be resected at least 5 cm proximal and distal to it.The tumor may metastasize to the liver via the bloodstream, or be implanted in the greater omentum or the peritoneum, and lymph node metastasis may be present. Radiotherapy and chemotherapy have certain efficacy. Infantile vascular ectodermal cell tumor: Stont and Murray firstly described vascular ectodermal cell tumor in 1942, which has characteristics in pediatrics, often called “vascular ectodermal cell tumor”, mostly seen in infants around 1 year old, only about 50% of them develop into malignant. Tumors grow in the subcutaneous tissue or transverse striated muscle, mostly in the lower limbs, especially in the femur and inguinal region, the head, face, mediastinum, retroperitoneum and pelvis. Tumor is a slow-growing painless mass, rich in blood vessels, so the local temperature may be slightly increased, sometimes there is a faint throbbing, but the above conditions rarely cause attention, the tumor may be accompanied by hypoglycemia, masculinization manifestations, the reason is unknown. Infantile vascular ectodermal cell tumor is mostly benign, which can be cured by local excision without radiotherapy or chemotherapy. The malignant ones should be treated with radiotherapy and chemotherapy after surgery, but there is no uniform opinion on its efficacy. 7.Malignant hemangioendothelioma: malignant hemangioendothelioma, also known as hemangiosarcoma, is rare in children. It mostly occurs in skin, soft tissue, liver and spleen. The incidence of the tumor is highest in skin, and the others are in the order of soft tissue, breast, liver, spleen and heart. Skin tumors are most common in the head and neck, followed by upper and lower limbs and trunk, manifesting as nodules above the skin with a diameter of 1 to 2 cm, and necrotic breakage is common on the surface. Pathologically, this tumor is easily confused with carcinoma and vascularized metastatic carcinoma, epithelioid synovial sarcoma, highly differentiated fibrosarcoma and intravascular papillary endothelial hyperplasia. Immunohistochemical staining helps in its differential diagnosis, e.g., factor VIII-associated antigen is synthesized by endothelial cells and is a specific marker for the tumor of its origin. Thorny bean agglutinin confirms the vascular endothelial nature of this tumor. This tumor has a high mortality rate due to extensive local spread or distant metastasis. The tumor commonly metastasizes to the lungs and liver, but also to regional lymph nodes, and is hypersensitive to radiotherapy. Only early limited extremity and trunk tumors may get radical surgery and resection. Lymphangiosarcoma: Lymphangiosarcoma is extremely rare in children and highly malignant. The tumor presents a tough mass, such as cyanotic ecchymosis, elevated above the skin surface, with fibrosis of the adjacent skin, subcutaneous tissue and muscle. The tumor tends to occur in the extremities and progresses proximally and distally. There are no effective treatment options for lymphangiosarcoma, the tumor is insensitive to radiotherapy, and amputation is often required in adult cases. All patients with chronic and congenital lymphedema should be examined regularly. Radical surgery is performed if there are symptoms of the tumor. The exact origin of synovial sarcoma is unknown and may originate from mesenchymal tissue that differentiates into synoviocytes. It is common in adolescents, with cases reported in infants. It is more common in males than females. Tumors occur in the lower extremities, most commonly in the knee, followed by the foot, ankle, and hip; in the upper extremities, they occur mainly in the joints of the wrist, shoulder, elbow, and hand. It can also occur in the head and neck, chest and abdominal wall. Clinically, a mass or an area of tumor is usually palpated near the joints, and children may have spontaneous pain or pressure pain, and rarely have serious dysfunction. Poorly differentiated tumors may have lethargy and impaired movement. Head and neck tumors may cause swallowing or respiratory difficulties.On radiographs, the tumor is a round or oval soft tissue mass that may be lobulated, and in about 20% of cases there is periosteal reaction or bone erosion. Calcification in the mass is more common in pediatric cases than in adults, and CT scan reveals a central necrotic area of the mass. Treatment is simple tumor resection without adjuvant therapy, and the tumor is prone to recurrence or spread. Lung metastasis occurs in 80% of tumors, 20% have regional lymph node metastasis, and 23% have bone metastasis. It is generally advocated to remove the tumor, but also to remove the muscle group near the tumor or do amputation, regional lymph node clearance. The effect of radiotherapy and chemotherapy is not certain, and chemotherapy is commonly used, such as vincristine, cyclophosphamide, actinomycin D (biotinomycin), zorubicin and so on. 9.Malignant mesothelioma: thoracic lesions mostly have chest pain and dyspnea, and pneumothorax and pleural effusion may occur. If the tumor occurs in the abdominal cavity or testicular sheath, the mass may be detected. Tumor has the tendency of severe local infiltration, extensive expansion along the plasma membrane surface, and children have the tendency of hematogenous metastasis to lungs, brain and other parts of the body. 10.Malignant nerve sheath tumor: 30%～43% of malignant nerve sheath tumors in children come from neurofibromatosis, while 50% of adults come from the main nerve trunk. This tumor is a gradually increasing mass on the surface of the body, accompanied by different degrees of pain. Early biopsy is indicated in cases of sudden enlargement of the mass or pain, as it may turn malignant. Malignant nerve sheath tumor is a kind of highly invasive tumor, which is easy to recur locally after resection, and the distant metastasis is mainly to the lungs, followed by the liver and bone. Patients with secondary neurofibromatosis are more malignant. Because the tumor is related to the main nerve trunk, usually local complete resection of the tumor, but also amputation, do not have to do lymph node dissection. The tumor radiotherapy is invalid, can be according to rhabdomyosarcoma program chemotherapy, but the effect is not certain. 11.Malignant mesenchymal tumor: it can occur in any part of the body, and is most common in the femur and retroperitoneum. Signs depend on tumor ulceration and invasion of surrounding tissues and organs. Femoral tumor can obstruct venous return and lower limb edema. Retroperitoneal tumors are often misdiagnosed as abdominal tumors. The general condition can deteriorate rapidly. Wide excision of the tumor should be performed, but this is usually not possible. Preoperative radiotherapy may reduce the size of the tumor for surgical resection. Postoperative radiotherapy may prolong the appearance of recurrence. The chemotherapy regimen is the same as the rhabdomyosarcoma regimen. 12.Glandular vesicular soft tissue sarcoma: the tumor is most common in children in the head and neck, especially in the orbit and tongue. In adults, it is more common in lower limbs. Because the tumor is rich in blood vessels, sometimes vascular pulsation can be felt, so it is usually asymptomatic and easy to be ignored. The tumor can metastasize to lung, brain and bone at early stage. Lymph node metastasis is rare. Treatment is radical surgery to remove the primary tumor and metastatic foci. Postoperative chemotherapy and radiotherapy should be applied jointly.