Validation of Updated Sarculator Nomogram for Primary Retroperitoneal Sarcoma in the United States

The Sarculator nomogram for retroperitoneal sarcoma (RPS) was recently updated to include the variable 'hospital volume', validated using primarily non-U.S.-based patient data. We sought to validate the updated nomogram using U.S. data, examine various cutoffs for high-volume center (HVC) designation (≥ 13 cases per year), and investigate factors that may further improve the nomogram.

A nationwide retrospective analysis using the National Cancer Database evaluated patients with RPS from 2010 to 2021. The Cox proportional hazards model was used to evaluate the impact of treatment at HVCs on overall survival (OS) using multiple case/year definitions. A model mimicking Sarculator's parameters was constructed then compared against sequential additions of variables found to be predictive in the initial analysis.

A total of 4537 patients were included, 352 of whom were treated at HVCs. Treatment at an HVC using this cutoff was associated with improved OS (hazard ratio [HR] 0.62; 95% confidence interval [CI] 0.43-0.90), whereas there was no association with OS using cutoffs of 10, 7, or 5 cases per year. Female sex (HR 0.81; 95% CI 0.69-0.94) and Charlson Comorbidity Index (CCI) score (HR 1.23; 95% CI 1.02-1.49) predicted improved survival. The addition of the HVC variable to the baseline model improved the fit of the model (likelihood ratio 10.23; p < 0.01) with the C-index going from 0.7126 to 0.7138. The inclusion of sex and CCI score further improved the fit of the model (likelihood ratio 44.41; p < 0.01) and increased the C-index to 0.7187.

The updated Sarculator with HVCs defined as ≥ 13 cases per year was validated using U.S.-only patients. The fit of the model was improved with the addition of sex and CCI score variables, and this should be explored in future studies of the Sarculator model.