Sintilimab for the Treatment of Locally Advanced, Metastatic, Recurrent, or Unresectable Undifferentiated Pleomorphic Sarcoma, SiARa Cancer Study

PRIMARY OBJECTIVE: I. To evaluate the efficacy of sintilimab in subjects with undifferentiated pleomorphic sarcoma (UPS) (overall response rate \[ORR\] at 12 weeks \[12W\] by Response Evaluation Criteria in Solid Tumors \[RECIST\] 1.1). SECONDARY OBJECTIVE: I. To evaluate the ORR (RECIST 1.1) and disease control rate (DCR), PFS, overall survival (OS), safety and duration of response (DOR) of sintilimab in subjects with UPS. EXPLORATORY OBJECTIVES: I. To evaluate the correlation between biomarkers in tumor tissue and efficacy, including but not restricted to PD-L1 expression level, tertiary lymphoid structures (TLS) transcriptome sequencing, single-cell sequencing, and multicolor immunohistochemistry (IHC) analyses. II. To evaluate the correlation between biomarkers in peripheral blood and efficacy, including but not restricted to soluble PD-L1, circulating tumor deoxyribonucleic acid (DNA) (ctDNA), identification/quantification of immunologic changes, and cytokine analyses. OUTLINE: Patients receive sintilimab intravenously (IV) over 30-60 minutes on day 1. Cycles repeat every 3 weeks for up to 24 months in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30 days and then every 60 days for 3 years.