A Study to Assess Overall Response Rate by Inducing an Inflammatory Phenotype in Metastatic BReast cAnCEr With the Oncolytic Reovirus PeLareorEp in CombinaTion With Anti-PD-L1 Avelumab and Paclitaxel - BRACELET-1 Study

This is an open-label randomized Phase 2, 3-cohort study to evaluate the safety and efficacy of pelareorep, paclitaxel and avelumab in Hormone Receptor+ (HR+)/Human Epidermal Growth Factor Receptor 2 negative (HER2-) with endocrine-refractory metastatic breast cancer. Patients will be randomized to one of three treatment cohorts: paclitaxel alone, pelareorep + paclitaxel, or pelareorep + paclitaxel + avelumab. A three patient safety run-in will be conducted in the cohort for pelareorep + paclitaxel + avelumab prior to beginning randomization into all three cohorts. Patients will give mandatory blood samples and optional tumor biopsies, which will be analyzed for biomarkers to determine the immunological changes within the tumor microenvironment and peripheral blood in patients treated with paclitaxel alone, in combination with pelareorep, and in combination with pelareorep and avelumab.