In 2000, Gordon et al. developed and investigated the physiological performance of a retroviral expression vector as a tumor-targeted gene delivery system, expressing a cytocidal dominant-negative construct of cyclin G1 (dnG1) in a metastatic liver model in nude mice [17], and in 2001, Gordon et al. showed that intravenous delivery of the mutated CCNG1 gene vector induced shrinkage of tumors in a nude mouse model of metastatic cancer, confirming cell death via apoptosis-mediated pathways [18]. This evidence concerns the gene CCNG1 and metastatic malignant neoplasm.