Comment on "Treatment of retroperitoneal sarcoma in Germany between 2000 and 2022: a retrospective analysis from the German Cancer Registry Group".

The nationwide registry analysis by Beck et al. provides valuable insights into treatment patterns for retroperitoneal sarcoma in Germany over two decades, highlighting increasing use of multivisceral resection and improved survival analyses. While the study establishes an important framework for evaluating rare cancers using registry data, several methodological issues may influence the interpretation of the reported temporal trends and clinical conclusions. First, the observed increase in multivisceral resection may partly reflect progressive improvements in registry documentation and procedure coding rather than a true change in surgical practice. Second, substantial missing data for tumor grade and metastatic status raise concerns regarding potential selection bias in survival analyses performed on complete cases without sensitivity analyses. Addressing documentation completeness and the impact of missing data would strengthen confidence in the reported findings and improve the applicability of registry-based evidence for clinical decision-making and future rare cancer research.