Abstract:Objective To explore the clinicopathological characteristics,diagnosis,treatment and prognosis of retroperitoneal [JP]dedifferentiated liposarcoma(DDL). Methods The clinicopathological and imaging data of 15 cases of retroperitoneal DDL from June 2013 to October 2019 were collected and analyzed,and the related literature was reviewed. Results Out of 15 cases,13 were male and 2 were female,with a median age of 54.3 years.The average diameter of tumor was about 15.8 cm.There were 12 cases of primary tumor and 3 cases of secondary tumor.CT scan suggested liposarcoma in only 7 cases.DDL tumors were completely resected in 13 cases and were not completely resected in 2 cases.Pathological examination showed atypical lipomatoid tumor/well differentiated liposarcoma (ALT/WDL) components in 13 cases and only dedifferentiated components in 2 cases.Immunohistochemistry showed that there were 15 cases of Vimentin-positive,13 cases of P16-positive,14 cases of murine double minute2(MDM2)-positive,11 cases of CDK4-positive,3 cases of SMA-positive and 1 case of Desmin-positive;the positive rate of Ki-67 was about 20%-60%.MDM2 gene amplification was detected by FISH in 15 cases.Of 12 cases followed up,9 relapsed and 3 of the relapsed cases died. Conclusions Retroperitoneal DDL is not sensitive to radiotherapy and chemotherapy.Surgical treatment is mainly used.It is easy to relapse after surgery.FISH detection of MDM2 gene amplification is of great value in the diagnosis of DDL.