PVR and breast cancer: Although CD155 is constitutively expressed at a low level in different tissues including vascular endothelial cells, spinal cord motor neurons, dendritic cells (DC), and macrophages [4,5,6], its overexpression correlates with poor prognosis in human malignancies of different origins such as non-small cell lung cancer (NSCLC), pancreatic cancer, sarcoma, melanoma, breast cancer, colorectal cancer, and multiple myeloma (MM) [7,8,9,10,11,12,13,14,15].