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

Must have received: cytotoxic chemotherapy

Patients must have received standard of care chemotherapy. No limits to prior lines of therapy.

Cannot have received: checkpoint inhibitor

Exception: Prior PD-1 and/or PD-L1 directed therapies are permitted.

Any patient who has experienced unacceptable toxicity on prior checkpoint inhibitor therapy as detailed below: 1. ≥ Grade 3 AE related to checkpoint inhibitor. 2. Ongoing ≥ Grade 2 immune-related AE associated with checkpoint inhibitor with the exception of endocrine toxicities as detailed below. 3. CNS, ocular or cardiac AE of any grade related to checkpoint inhibitor. * NOTE: Patients with a prior or ongoing endocrine AE are permitted to enroll if they are stably maintained on appropriate replacement therapy and are asymptomatic.

Cannot have received: investigational agent

Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 weeks of the first dose of treatment.

Cannot have received: chemotherapy, immunotherapy, targeted small molecule therapy, or radiation therapy

Has had prior chemotherapy, immunotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1

Cannot have received: allogeneic stem cell or solid organ transplantation

Prior allogeneic stem cell or solid organ transplantation