PVR and neoplasm: Although an increasing number of oncolytic agents have been developed, few reports have elucidated the mechanism(s) of tumor tropism: oncolytic poliovirus recognizes the tumor-overexpressed CD155 [36–38]; reovirus preferentially replicates in cells with activated oncogenic Ras signaling [39–41]; vesicular stomatitis virus (VSV) requires defects in the IFN pathway [42–44]; and M1 requires ZAP deficiency [7, 45].