Measuring if Immunotherapy Plus Chemotherapy is Better Than Chemotherapy Alone for Patients With Aggressive Poorly Differentiated Sarcomas

Inclusion Criteria: * Patient must be \>= 18 years of age * Patient must have a confirmed histopathologic diagnosis of dedifferentiated liposarcoma (DDLPS), undifferentiated pleomorphic sarcoma (UPS) or a related poorly differentiated sarcoma. Because UPS can sometimes exist in a spectrum among related diagnoses, the following additional diagnostic will be allowed, but not limited to: * Pleomorphic sarcoma with inflammation or with limited areas of differentiation * Pleomorphic sarcoma with giant cells * Malignant fibrous histiocytoma (including storiform-pleomorphic and inflammatory subtypes) * Myxofibrosarcoma * Poorly differentiated sarcoma not otherwise specified (NOS) * Undifferentiated spindle cell sarcoma * Poorly differentiated spindle cell sarcoma NOS Any of these subtypes may have areas of focal myogenic differentiation * Patient must have metastatic or unresectable sarcoma * Patient must not be pregnant or breast-feeding due to the potential harm to an unborn fetus and possible risk for adverse events in nursing infants with the treatment regimens being used. All patients of childbearing potential must have a blood test or urine study within 14 days prior to randomization to rule out pregnancy. A patient of childbearing potential is defined as anyone, regardless of whether they have undergone tubal ligation, who meets the following criteria: * Has achieved menarche at some point * Has not undergone a hysterectomy or bilateral oophorectomy; or …