Methods are provided for treatment of cancer in a subject's body by intraluminal delivery of oncolytic viruses through a balloon catheter or alternative mechanism inserted in a blood vessel or duct leading to a target site of the cancer tissue, or for somatic cell gene therapy of single defective gene-caused other diseases or disorders by similar intraluminal delivery of non-oncolytic viruses to a target site of affected tissue and cells of the disease or disorder, wherein during delivery of the oncolytic or non-oncolytic virus, the designated vessel or duct is selectively occluded at both ends of the target site by two spaced-apart inflated balloons of the catheter to block perfusion therethrough and allow control of the volume of virus delivered to the target site so as to increase concentration and pressure of the virus thereat sufficient to enable viral penetration of an endothelial barrier of the vessel or duct without compromise thereof and into diseased cells in the vicinity of the target site toward achieving a desired therapy.
