WELL-DIFFERENTIATED LIPOSARCOMA OF THE RETROPERITONEUM - A CLINICOPATHOLOGICAL ANALYSIS OF 20 CASES, WITH PARTICULAR ATTENTION TO THE EXTENT OF LOW-GRADE DEDIFFERENTIATION

Dedifferentiated liposarcoma (DDL) has been defined as a tumor compose d of well-differentiated liposarcoma (WDL) associated with or progress ing to a nonlipogenic, high-grade sarcoma. One might expand this defin ition of DDL to include low-grade dedifferentiation (LGDD), because tu mors with LGDD alone are capable of metastasizing. We studied 20 cases of retroperitoneal WDL with or without LGDD and/or high-grade dediffe rentiation (HGDD) to semiquantitate the amount of WDL, LGDD, and HGDD in each case and to correlate the amounts of these components with cli nical outcome. For each case, a composite estimate of each of these co mponents was obtained. Thirteen patients (65%) of 20 had an adverse ou tcome (AO). Within this group, metastatic disease developed in 3 patie nts, 2 of whom had areas of HGDD (40% and 20%) in their initial excisi ons, whereas 1 patient had 30% LGDD and 0% HGDD. Of the patients with AOs, 12 (92%) had LGDD areas, 4 (31%) had HGDD areas, and 1 (8%) had p ure WDL. Of the seven patients without AOs, three had recurrences, but metastatic disease did not develop in any. All of these seven patient s had some element of WDL, five (71%) had LGDD areas, two (29%) had HG DD areas (20% in both cases), and two (29%) had pure WDL. There was no significant difference in clinical outcome between those patients wit h WDL and those with WDL/LGDD or WDL/LGDD/HGDD. We conclude that recur rences develop in most patients with retroperitoneal WDL and that most of these patients die as a result of local effects of the tumor. Meta stases are rare and may occur in patients with tumors with either LGDD , HGDD, or both but do not occur in pure WDL. Neither the amount of LG DD nor HGDD correlates with clinical outcome. LGDD areas, as defined i n this study, are commonly seen in de novo retroperitoneal WDLs.