A Study in Advanced or Metastatic Gastrointestinal Cancers Exploring Treatment Combinations With Pelareorep and Atezolizumab

Cohorts 1-5 Inclusion Criteria: * ECOG performance status of 0 or 1 * Have measurable lesions per RECIST v1.1 * Patients must have adequate hematological, renal, and hepatic function * Have recovered to ≤grade 1 or baseline for all adverse events (AEs) due to previous therapies or surgeries. * For female patients of childbearing potential and male patients with partners of childbearing potential, agreement to use a highly-effective form(s) of contraception and to continue its use for 6 months after the last dose of study drug. Exclusion Criteria: * Undergone systemic chemotherapy, radiotherapy, or surgery, \<4 weeks before study treatment. * Received previous treatment with immune checkpoint inhibitors * Uncontrolled or severe cardiac disease * Active, uncontrolled infections * Symptomatic brain metastasis * Interstitial lung disease with symptoms or signs of activity. * Autoimmune disease that has required systemic treatment in the past 2 years with disease modifying agents, corticosteroids, or immunosuppressive drugs. * A seizure disorder that requires pharmacotherapy. * Known hypersensitivity to any of the study drugs, study drug classes, or excipients in the formulation. * A non-healing wound, non-healing ulcer, or non-healing bone fracture within 4 weeks prior to the start of study drug. * Women who are pregnant or breastfeeding. * A diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy * Any vacc…