A genetically stable Salmonella typhimurium strain, attenuated by chromosomal deletion of the purI and msbB genes, with tumor-targeting activity. In rodent models, salmonella VNP20009 has been shown to selectively accumulate and grow in a variety of tumor types, inhibiting the growth of primary and metastatic tumors. This agent may be genetically engineered to contain transgenes that express therapeutic agents or cell surface tumor-associated antigen-specific antibodies, such as CEA-specific antibodies, which may improve its tumor targeting and therapeutic potential.