(P 330) TREATMENT VARIATIONS, OUTCOMES AND PATTERNS OF RECURRENCE AFTER CURATIVE INTENT TREATMENT FOR PRIMARY RETROPERITONEAL SARCOMAS IN LATIN AMERICA. FIRST COLLABORATIVE LATAMSARC STUDY

Objective: Retroperitoneal sarcomas (RPS) are rare tumors composed of several well-defined histologic subtypes. The objective of this study was to assess the epidemiology, treatment patterns, and outcomes of patients with retroperitoneal sarcoma in Latin America. The aim of this study was to analyze patterns of recurrence and treatment variations in a large population of patients treated at reference centers.

Methods: This retrospective descriptive study utilized an electronic database of medical records from LATAMSARC (a group studying sarcomas consisting of different centers in various countries in Latin America, including Argentina, Chile, Costa Rica, Mexico, and Peru). Adult patients (≥18 years) with retroperitoneal sarcoma who underwent surgery at six cancer centers in Latin America were included. Key outcomes were practice patterns, overall survival (OS), and progression-free survival (PFS).

Results: Three hundred patients with retroperitoneal sarcomas met the inclusion/exclusion criteria. The mean age was 53 years (SD 13.37), with 53% being male and 47% female. Out of these, 272 (90.7%) were located in the extrapelvic retroperitoneum, and 28 (9.3%) were in the pelvic retroperitoneum. The tumor size was 23.53 cm (SD 13.8 cm). The most common subtypes were well-differentiated liposarcoma (30.5%), dedifferentiated liposarcoma (24.6%), leiomyosarcoma (10.8%), malignant peripheral nerve sheath tumor (6.2%), solitary fibrous tumor (1.5%), and other or non-classifiable (8.4%). Compartmental resection was performed in 34.7% of cases, involved organ resection in 26.3%, simple resection in 32.7%, 6% were deemed unresectable, and 0.3% had missing data. Tumor rupture was reported in 15 cases (5%). The kidney was the most frequently resected organ, with 123 cases (41%), followed by the right colon in 52 cases (17.3%) and the left colon in 46 cases (15.3%). Complications with Clavien-Dindo scale >3 occurred in 56 cases (18.7%), with bleeding being the most frequent in 28 cases. Sixty-two patients required intensive care unit stay, the duration of surgery was 240 minutes (SD 131 minutes), and the hospital stay was 11.9 days (SD 9.6). The median follow-up was 26 months (Interquartile range: 11-39). Median overall survival (OS) was 52.20 months [95% confidence interval (CI): 44.95-59.44]. The local recurrence (LR) rate was 54.3 % with a median of 47.012 months (95% CI: 40.33, 53.69) in this cohort of patients.

Conclusion: This study provides information on the epidemiology, treatment patterns, and outcomes of retroperitoneal sarcomas in a group of reference centers in Latin America. These results represent the largest body of evidence on retroperitoneal sarcomas in Latin America.