RB1 and breast cancer: CG0070, a genetically engineered oncolytic adenovirus was designed to selectively replicate in BC cells with defects in the retinoblastoma (Rb) tumor suppressor pathway, and concurrently produce granulocyte-macrophage colony-stimulating factor (GM-CSF) to stimulate immune-mediated anti-tumor effects (Burke et al., 2012).It uses the human E2F-1 promoter, which is active in cells with a compromised Rb pathway, to drive the expression of the key viral gene E1A, thereby ensuring that viral replication occurs selectively in tumor cells lacking functional Rb.