Retroperitoneal liposarcomas: Follow-up analysis of dedifferentiation after clinicopathologic reexamination of 86 liposarcomas and malignant fibrous histiocytomas

BACKGROUND. Dedifferentiated liposarcoma (DDL) juxtapose components of well-differentiated liposarcoma (WDL) and nonlipogenic sarcoma. Malignant fibrous histiocytoma (MFH) is no longer considered a homogeneous entity, but rather as the common morphologic appearance of various subtypes of sarcomas. The objectives of the current retrospective study were: 1) to analyze the relation between DDLs and tumors previously diagnosed as MFHs; 2) to trace the evolution of liposarcomas, and 3) to assess the consequences of dedifferentiation. METHODS. Between 1974 and 2001, 86 patients with retroperitoneal liposarcoma (61 patients) or MFH (25 patients) underwent surgery at Institut Bergonie in Bordeaux, France. Histologic review was performed and tumors reclassified as WDL or DDL were retained for further clinicohistologic study. Subsequently, initial presentation and all recurrences were analyzed. RESULTS. The 61 liposarcomas consisted of 21 WDLs and 35 DDLs; 17 MFHs were reclassified as DDL. In all, approximately half of the retroperitoneal liposarcomas and MFHs were found to be DDLs. The DDLs presented with a smaller size (20 cm vs.30 cm; P = .05) but a lower rate of complete resection (72% vs.90%; P = .015) and remission (72% vs. 100%; P = .0015). Dedifferentiated recurrence was evidenced in 7 WDLs. Ten DDLs presented with metastatic evolution. DDLs demonstrated a tendency toward lower rates of 5-year overall survival (55% vs. 82%; P = .075). CONCLUSIONS. Most occurrences of retroperitoneal liposarcomas and MFHs are in fact DDLs and dedifferentiated recurrence of WDLs is frequent. Retroperitoneal DDLs present a lower rate of complete remission than WDLs and a risk of metastatic recurrence. Therefore, extensive histologic analysis of WDLs is required to identify an undifferentiated component and avoid misdiagnosis of DDL.