Study of All-Trans Retinoic Acid (ATRA) and Cemiplimab in Patients With Advanced Leiomyosarcoma

PRIMARY OBJECTIVES I. To determine the efficacy of the combination of ATRA and Cemiplimab in patients with metastatic/locally advanced -unresectable LMS by assessing objective response (ORR), Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 and immune mediated Response Evaluation Criteria for Solid Tumors (iRECIST). SECONDARY OBJECTIVES I. To study the efficacy of the combination of ATRA and Cemiplimab in patients with advanced LMS, including progression-free survival (PFS), disease control rate (DCR), and overall survival (OS) based on modified RECIST version 1.1 and iRECIST. II. To determine the safety and tolerability of the combination of ATRA and Cemiplimab in patients with metastatic/locally advanced -unresectable LMS based upon the Common Terminology Criteria for Adverse Events (CTCAE) version 5 criteria. EXPLORATORY OBJECTIVES I. To study the effect of ATRA on the levels of myeloid-derived suppressor cells (MDSCs) in the peripheral blood of study patients OUTLINE: Patients receive ATRA orally (PO) on days -2 to 0 followed by cemiplimab intravenously (IV) on day 1 of each cycle. ATRA treatment is given for 3 cycles. Cycles repeat every 21 days in the absence of disease progression or unacceptable toxicity. Patients undergo urine sample collection during screening, and computed tomography (CT) scan/magnetic resonance imaging (MRI) and blood sample collection throughout the study. After completion of study treatment, patients are followed up every 12-16 weeks. .