(P 332) SURGICAL OUTCOMES OF RETROPERITONEAL LIPOSARCOMA - SINGLE INSTITUTIONAL STUDY N JAPAN -

Objective: Liposarcoma (LPS) is the most common histologic type of retroperitoneal sarcoma, accounting for 50-60% of all cases. Complete tumor resection is the only promising strategy associated with survival benefits. Although the survival outcome of dedifferentiated liposarcoma (DDLPS) is worse comparing to well-differentiated liposarcoma (WDLPS), surgical outcomes of those are not described precisely.
The aim of this study is to determine whether surgical outcomes differ between DDLPS and WDLPS.

Methods: We retrospectively examined 192 patients with primary retroperitoneal liposarcoma who underwent initial surgery at the National Cancer Center Hospital in Japan between April 2011 and March 2022. Clinicopathological and surgical information were analyzed using the χ2 and Mann-Whitney tests. Survival analyses with overall survival (OS) and disease-free survival (DFS) were performed using the Kaplan-Meier method. Prognostic factor analysis for survivals was performed using Cox regression analysis.

Results: The histological subtypes included DDLPS (n=121; 61.7%) and WDLPS (n=71; 36.2%). Median follow-up time of all patients was 47 months (range: 3–155 months). Median age at diagnosis was 63 years old (17–82 years old) and 56.6% (n=111) of patients were male. Median operation time was 281 minutes (68–942 minutes) and median blood loss was 658 ml (0–9,524 ml). In 157 cases (80.1%), concomitant organ resection with tumor was performed, with nephrectomy being the most common surgery. DDLPS was characterized by longer operative time (314 vs. 234 minutes, P< 0.001), more blood loss (815 vs. 447 ml, P< 0.001), and more frequent concomitant organ resection (86.8% vs. 73.2%, P=0.003) than WDLPS. Median OS was not reached, the 2-, 5-, and 7-year OS were 89.6%, 77.7%, and 74.6%, respectively. Median DFS was 32 months (95% CI: 5.75-16.24 months), and DDLPS showed worse survival (21.8 months vs. 77.9 months, p< 0.001). The 2-, 5-, and 7-year DFS rates were 62.2%, 32.0%, and 24.3%, respectively. Multivariate analysis for OS demonstrated that a positive margin was at a higher risk of recurrence.

Conclusion: Reviewing the surgical treatment of primary retroperitoneal liposarcoma at our hospital, we found that OS date was good and comparable to the reports of former various authors. This study showed that when LPS was treated by surgery alone, surgery for DDLPS was more invasive that that for WDLPS.