(P 301) RETROPERITONEAL SARCOMA: SINGLE CENTER EXPERIENCE IN LATIN AMERICA. DO WE HAVE DIFFERENT SARCOMAS WHEN COMPARED TO THE REST OF THE WORLD?

Objective: Retroperitoneal sarcomas are rare tumors and international collaborations have been the main instrument for understanding tumor biology and prognosis. In this study we aim to describe the characteristics of patients with retroperitoneal sarcomas at our institution and compare them to those reported around the globe.

Methods: This is an observational retrospective study of retroperitoneal sarcoma patients who were surgically treated at Fundación Colombiana de Cancerología Clínica Vida in Medellín, Colombia, from 2016 to 2025. Categorical variables: absolute/relative frequencies. Numerical variables: medians, interquartile ranges [IQR]. 5-year overall survival (OS) and relapse-free survival (RFS) estimated via Kaplan-Meier. Cox proportional hazards regression identified OS/RFS-associated factors. A nonsystematic review of the literature was performed, and data from around the globe was compared to the present data.

Results: Seventy-four patients were included: 63.5% women, median age 61 [IQR: 50.2–69] years. Median size is 15 [IQR: 11.7–20] cm. Most frequent histological subtypes: dedifferentiated liposarcoma (37.8%), well-differentiated liposarcoma (36.5%), and leiomyosarcoma (12.2%). Histological grade I was 32.6%, grade II 18.3%, and grade III 48.9%. Median follow-up 24 [IQR: 11-47] months. 5-year OS: 54% (95% CI: 42–70); RFS: 44% (95% CI: 31–62). Histology other than well-differentiated liposarcoma and intraoperative blood transfusions were associated with worse OS and RFS.

Conclusion: When compared to The Transatlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG) and other European and North American databases, we have more women with retroperitoneal sarcomas but a similar proportion when compared to a recently published report from Brazil. The histological distribution is similar to TARPSWG, but we have fewer leiomyosarcomas when compared to North America. We had a proportion of grade III sarcomas close to 50%, higher than TARPSWG and other European series but similar to Latin and North American reports. We have a lower median follow-up time compared to most series and lower OS when compared to TARPSWG but similar to the USA, UK, and Mexico.