REtroperitoneal SArcoma Registry (RESAR): Prospective Collection of Primary Retroperitoneal Sarcoma Patient's Data, Radiological and Pathological Material for the TransAtlantic Retroperitoneal Sarcoma Working Group

Surgery is currently the only potentially curative treatment modality for localized retroperitoneal sarcoma (RPS). Available studies regarding oncologic outcomes are mainly retrospective in nature, and RPS are recognized as a rare disease. Therefore, prospective analysis of high quality data is a top priority. Primary Objectives of this study are: * to prospectively collect standardized clinical data and radiological and pathological material from primary RPS patients treated with surgery at reference centers. * patient outcome will be evaluated in terms of overall survival (OS), disease-free survival (DFS), crude cumulative incidence (CCI) of local recurrence (LR) and distant metastasis (DM). Secondary Objectives: * to estimate the efficacy and safety of surgical treatment, including extended surgical approach to primary RPS; * to prospectively evaluate the impact of multimodality therapy, including radiation therapy and chemotherapy; * to identify clinical, radiological and pathological characteristics that may influence the oncological outcome or may be used as predictors of LR/DM/OS. These may be important biomarkers of disease; * to utilize collected pathological material for research collaborations.