(P 302) PREDICTORS AND OUTCOMES OF RECURRENT RETROPERITONEAL SARCOMA: A SINGLE-CENTER LATIN AMERICAN COHORT STUDY

Objective: Retroperitoneal sarcomas (RPS) are rare mesenchymal tumours arising in the retroperitoneal space, accounting for approximately 15% of all soft-tissue sarcomas and characterised by diverse histologic subtypes and typically large tumour size. Tumour-specific factors—most notably high histologic grade, increasing tumour size, and specific subtypes such as leiomyosarcoma and dedifferentiated liposarcoma—have been consistently associated with an elevated risk of distant recurrence, which negatively impacts long-term survival. Despite advances in surgical technique, systemic recurrence rates remain substantial and portend a poor prognosis.

Methods: We performed a retrospective cohort analysis of 142 adult patients (mean age 51.7 ± 14.0 years; 54.2% male) with histologically confirmed primary (n = 103) or recurrent (n = 39) RPS who underwent curative-intent resection between January 2019 and December 2024 at a single high-volume tertiary referral centre in Latin America. Baseline data included demographics, histologic subtype, FNCLCC grade, maximum tumour diameter, margin status, and presence of histologically confirmed vascular invasion. Systemic recurrence–free survival (SRFS) and overall survival (OS) were estimated by Kaplan–Meier methods.

Results: Median follow-up was 39 months (IQR 22–63). Systemic recurrence occurred in 17 patients (12.0%) at a median interval of 40 months (IQR 28–62). In univariate analysis, FNCLCC grade III (vs I–II), recurrent presentation, and tumour size > 20 cm were associated with shorter SRFS. In multivariate analysis, only high histologic grade remained an independent predictor of systemic recurrence (hazard ratio [HR] 3.12, 95% CI 1.45–6.71; p = 0.003), with the highest recurrence rates observed in leiomyosarcoma (15.6%) and dedifferentiated liposarcoma (13.8%) subgroups. Histologic subtype per se was not predictive of systemic recurrence unless coupled with high grade, and organic invasion was not associated with recurrence risk in our cohort (p = 0.56). Five-year OS was 67%.

Conclusion: In this single-centre Latin American cohort, high histologic grade—but not histologic subtype alone—was the principal determinant of systemic recurrence in RPS, particularly in leiomyosarcoma and dedifferentiated liposarcoma. Histologically confirmed organic invasion did not predict recurrence.