RecruitingPhase 1Drug trialEvaluation of Abemaciclib and Radiation Therapy Before Surgery for the Treatment of High-Risk Adipocytic Retroperitoneal SarcomaThis phase I trial tests the safety, side effects, and best dose of abemaciclib and how well it works with radiation therapy before surgery in treating patients with high-risk adipocytic retroperitoneal sarcoma. Abemaciclib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. Giving abemaciclib together with radiation therapy before surgery may shrink tumors in patients with high-risk adipocytic retroperitoneal sarcoma.