A Window-of-opportunity Study of Pelareorep in Early Breast Cancer

This is a window of opportunity non-randomized exploratory study to evaluate the safety and anti-tumor immunogenicity of pelareorep -/+ atezolizumab in five different cohorts in women with operable early breast cancer. After enrollment, pelareorep will be administered at 4.5 × 1010 TCID50 intravenously on days 1, 2, 8 \& 9. Other therapies will be administered according to the assigned treatment cohort. After an initial biopsy (diagnostic biopsy in most cases), a second biopsy will be performed on Day 3. Patients will continue the planned treatment until day 21(±5), when a third biopsy will be performed. This third biopsy can be the surgical specimen if patient was scheduled for primary surgery, or a core biopsy if patient will undergo neoadjuvant treatment. Blood samples will be collected throughout the study at three time points, Day 1, Day 3, and End of Treatment. Patients will receive treatment for 3 weeks prior to surgery or neoadjuvant therapy. Thereafter, patients will either be considered for definitive surgery or primary medical treatment (e.g. neoadjuvant chemotherapy) at the discretion of the treating physician. Surgery or biopsy prior to neoadjuvant chemotherapy should be done within 3 weeks (±5 days) from the start of the study treatment. The end of study visit will be performed at the day of surgery. A safety follow-up, the end of study visit, will be done at 28 days (± 7 days) after the last dose of treatment received