RecruitingPhase 3ProcedureSurgery With or Without Neoadjuvant Chemotherapy in High Risk RetroPeritoneal SarcomaThis is a multicenter, randomized, open label phase lll trial to assess whether preoperative chemotherapy, as an adjunct to curative-intent surgery, improves the prognosis of high risk DDLPS (dedifferentiated Liposarcoma) and LMS (Leiomyosarcoma) patients as measured by disease free survival. After confirmation of eligibility criteria, patients will be randomized to either the standard arm or experimental arm.