Sintilimab for the Treatment of Locally Advanced, Metastatic, or Recurrent Angiosarcoma, the SiARa Cancer Study

Inclusion Criteria: * Histopathologically confirmed unresectable, locally advanced, recurrent or metastatic angiosarcoma * Intolerant to or progressed on at least one line of systemic chemotherapy. Patient ineligible for cytotoxic chemotherapy are eligible * Aged \>= 18 * Can provide archival or fresh tissues for optional correlative analysis * Have at least one measurable lesion as per RECIST version (v)1.1 * Eastern Cooperative Oncology Group (ECOG) performance status =\< 1 * Absolute neutrophil count (ANC) \>= 1.0 x 10\^9/L * Platelet (PLT) count \>= 75 x 10\^9/L * Hemoglobin (HGB) \>= 8.0 g/dL * Total bilirubin (TBIL) =\< 1.5 x upper limit of normal (ULN) * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =\< 2.5 x ULN in subjects without hepatic metastasis; ALT and AST =\< 5 x ULN in subjects with hepatic metastasis, gamma-glutamyl transferase (GGT) =\< 10 x ULN * Urine protein \< 2+ from random sample or \< 1 g from 24-hour urine collection * Serum creatinine =\< 1.5 x ULN or calculated creatinine clearance rate (Ccr) \>= 50 mL/min by Cockcroft-Gault formula * Adequate coagulation function, defined as international normalized ratio (INR) =\< 1.5 or prothrombin time (PT) =\< 1.5 x ULN; if the subject is receiving anticoagulant therapy, the results of coagulation tests need to be within the acceptable range for anticoagulants * Expected survival \>= 12 weeks * Subject (female subjects of childbearing age or male subjects whose partners are of childbear…