Doxorubicin Plus Dual Checkpoint Blockade for Soft Tissue Sarcomas

The primary endpoint for the study is PFS6mo by RECIST 1.1. The sample size calculation is based on a Simon Two-Stage design with incorporation of early stopping rules for safety and futility (See section 9 for statistical considerations). The Investigators will enroll up to 35 patients on the study to obtain 28 evaluable patients for the primary endpoint. Safety of the combination will be evaluated after the first six patients complete the DLT observation period of 9 weeks. This lengthy DLT period is designed to capture safety and toxicity profile, understanding that immune-related toxicities from checkpoint inhibitors may not emerge immediately. This will also ensure adequate evaluation of potential cardiac and hepatic toxicity from combination doxorubicin and checkpoint inhibitor therapy. If two or more patients experience DLT in the initial safety lead-in cohort, the regimen will be declared intolerable. Any patients who do not complete study therapy through the 9-week DLT observation period for any reasons other than toxicity will be replaced for safety lead-in assessment. If fewer than two patients experience DLT, the investigators will proceed to expansion to complete enrollment of 15 patients in Stage 1. Following enrollment of stage one, accrual will pause for analysis of efficacy. If 6 or fewer of the 15 patients are progression-free at 6 months, the investigators will halt the study for futility. If 7 or more patients are free from progression, then the investigators will proceed with enrollment of 13 additional patients to complete stage 2. the investigators are powered to detect improvement in 6-month PFS rate to 63.4% with the combination over the 43.4% historical PFS6mo.