CINSARC and Sarculator in Patients with Primary Retroperitoneal Sarcoma: A Combined Analysis of Single-Institution Data and the EORTC-STBSG-62092 Trial (STRASS).

Purpose: The Complexity INdex in SARComas (CINSARC) predicts the metastatic risk in patients with soft-tissue sarcoma. The aims of this study were to provide the first independent validation of CINSARC in patients with retroperitoneal sarcoma (RPS) and evaluate whether CINSARC could enhance the performance of Sarculator.

Experimental Design: A retrospective cohort included patients with primary localized RPS resected with curative intent (2011-2015) at a single institution. The STRASS cohort comprised patients from the surgery-only arm of the EORTC-STBSG-62092 (STRASS) trial who had undergone CINSARC categorization. Patients were classified as CINSARC low-risk (C1) versus high-risk (C2). Primary study endpoints were overall survival (OS) and disease-free survival (DFS). Sarculator performance was assessed in terms of discrimination (the Harrell C-index) and calibration (calibration plots and the Brier score) before and after adding CINSARC.

Results: The study cohorts included 104 and 69 patients, respectively, with similar OS. In a pooled cohort, in multivariable analysis for OS considering Sarculator and CINSARC, only Sarculator was significantly associated with OS [HR, 1.93; 95% confidence interval (CI), 1.35-2.74; P < 0.001]. In multivariable analysis for DFS, both Sarculator (HR, 1.51; 95% CI, 1.09-2.09; P = 0.013) and CINSARC (HR, 2.01; 95% CI, 1.26-3.23; P = 0.004) were significantly associated with DFS. However, the addition of CINSARC did not improve Sarculator's discrimination or calibration for either OS or DFS.

Conclusions: This study validates CINSARC as a prognostic predictor for OS and DFS in patients with primary RPS. CINSARC did not improve the performance of Sarculator, suggesting that its addition to the Sarculator may not provide added clinical benefit.