This app is meant to be used only by physicians and it is not meant to make clinical decisions (the clinical usefulness of the two models has not been tested) but to be used as an informative tool to improve the predictive capability of a physician. Two kinds of predictions are possible: - RPS: 5-year overall survival (OS) and 5-year disease-free survival (DFS) in primary resected retroperitoneal sarcoma (RPS) patients. . - STS: 5- and 10-year overall survival (OS) and cumulative incidence of