Methods for treating tumors and malignant tumors in regions that are adjacent to the gastrointestinal tract are provided. Therapeutically effective amounts of transformed bacteria are administered to subjects in need of treatment. Bacteria are transformed to produce proteins exhibiting therapeutic effects. These therapeutic effects can be the production of an enzyme that catalyzes the conversion of a prodrug into a drug and/or a protein that has therapeutic activity on its own. Bacteria may be provided to the gastrointestinal tract of the subject in need of treatment or preventative measures. In some cases, a prodrug is additionally administered.
