What are the characteristics of retroperitoneal tumors? Retroperitoneal tumors are mostly of soft tissue origin, and soft tissue tumors are an extremely diverse group. Therefore, retroperitoneal tumor is a kind of tumor with many pathological types, insidious onset, not easy to be detected early, and once diagnosed, it often involves many blood vessels, nerves or organs behind the peritoneum, which makes surgical resection difficult, and it is not sensitive to chemotherapy and radiotherapy, so it is a kind of difficult tumor that “dare not ask or no one asks” this is the clinical treatment characteristics of retroperitoneal tumor. In addition, retroperitoneal tumor has its unique “biological characteristics”. Retroperitoneal tumor, four same biological characteristics. 1, the tumor is expansive growth, but generally does not have infiltration; 2, the tumor generally has an intact envelope; 3, not easy to appear distant metastasis; 4, capacity appears postoperative local recurrence; Therefore, retroperitoneal tumor is different from other cancers, because of its non-invasive growth and no clinical manifestation in early stage, most of them have grown huge at the time of consultation, and show compression caused by huge tumor and abdominal organs grabbing abdominal space. Most of the tumors are already huge when they are diagnosed. Because of late detection, difficult surgery and malignancy, the overall outcome is not satisfactory. Despite this, if we understand the common biological characteristics of retroperitoneal tumors, we should not easily give up surgical resection of larger or even huge retroperitoneal tumors, and we should strive for reoperation or multiple operations even for recurrent cases. Especially, early detection by ultrasound is more important.