RecruitingClinical trialMultimodal Immune Characterization of RAre Soft Tissue Sarcoma - MIRAS Project From SARRA (SARcome RAre) Project of the French Sarcoma GroupThis trial is a translational, open-label, multi-sites, prospective and retrospective cohort study of 500 patients aimed at clinical and biological characterization of sarcoma of rare subtype. 400 patients will be included in this prospective cohort study; they will be identified in the investigating centers in the context of either routine care or a clinical study protocol. Retrospective cases of patients (100 cases in total) will be identified in all centers through the GSF/GETO clinical databases already setted up (including the clinical base Conticabase).