Protocol and procedure of the “GFP-CTC Assay”. Each 7.5-ml peripheral vein blood sample was obtained from patients before surgery and from volunteers. The samples were drawn into tubes containing citric acid, phosphoric acid and dextrose. The samples were centrifuged and the plasma phase was removed. After cell washing using PBS and Roswell Park Memorial Institute medium, the samples were infected with 4 × 108 PFU of OBP-401 virus. OBP-401 virus was inactivated and cells were fixed with 2% paraformaldehyde (PFA). The samples were treated with a surface-active agent to degrade red and white blood cells. Two glass slide samples from 7.5 ml blood were prepared for microscopic analysis. All GFP-positive cells on the two slides were counted using a computer-controlled fluorescent microscope.