Retroperitoneal sarcoma is relatively uncommon, constituting only 10–15 percent of all soft tissue sarcomas. The most common histologic types of RPS are liposarcoma and leiomyosarcoma. Retroperitoneal sarcoma is classified based on the amount of lipid inside the cells, the mucoid lipid and the degree of cell differentiation. It is classified into the well-differentiated, myxoid, round cell, pleomorphic and dedifferentiated types and the commonest is the pleomorphic type. Dedifferentiated liposarcomas are defined by the presence of sharply demarcated regions of non-lipogenic sarcomatous tissue within a well-differentiated tumor. This type has a vague prognosis compared to other types of sarcoma and making the histological diagnosis can be difficult. Dedifferentiated liposarcoma commonly develops in the retroperitoneum, limbs, testis, and spermatic cord. Retro peritoneal sarcoma typically produces few symptoms until they are large enough to compress or invade surrounding structures. Most tumors are already large and locally advanced at the time they are first detected. Here, we reported a case that came to medical attention as an incidentally discovered large abdominal mass in an asymptomatic or minimally symptomatic, later the mass was successfully removed and free from symptoms.

腹膜后肉瘤相对少见，仅占所有软组织肉瘤的 10-15%。最常见的 RPS 组织学类型是脂肪肉瘤和平滑肌肉瘤。腹膜后肉瘤根据细胞内脂质的含量、粘液脂质和细胞分化程度进行分类。分为高分化型、粘液型、圆细胞型、多形型和去分化型，最常见的是多形型。去分化脂肪肉瘤的定义是在分化良好的肿瘤内存在非脂肪性肉瘤组织的界限分明的区域。与其他类型的肉瘤相比，这种类型的预后模糊，进行组织学诊断可能很困难。去分化脂肪肉瘤常见于腹膜后、四肢、睾丸、和精索。腹膜后肉瘤通常不会产生任何症状，直到它们大到足以压迫或侵入周围结构。大多数肿瘤在第一次被检测到时已经很大并且局部晚期。在这里，我们报告了一个病例，因为偶然发现无症状或轻微症状的腹部大包块而就医，后来包块被成功切除并且没有症状。