The purpose of this work was to carry out preclinical toxicity and bio-distribution studies required for regulatory approval of a clinical trial application for Phase I clinical studies of ONCOS-102 (Ad5/3-D24-GM-CSF) for therapy of advanced cancers (NCT01598129). The study design, route of administration and dosage differs from the clinical protocol and in more detail, investigate bio-distribution and toxicological profile of ONCOS-102 treatment in animal model. The study was carried out in 300 hamsters divided into nine test groups-three bio-distribution groups and six groups for analysis of toxicity. Hamsters received ONCOS-102 by intracardial, intraperitoneal or subcutaneous injections. Additionally, one group was administered twice a week with intraperitoneal injections of Cyclophosphamide. The control animals were administered with NaCl solution without ONCOS-102 in the same volume and the same way. No adverse effects of repeated administration of ONCOS-102 including body weight, food consumption, hematology and clinical chemistry parameters, histopathology and bio-accumulation were observed in the course of 6-month administration and following 3- month recovery period. All obtained findings indicate the treatment clinically safe.