The aim of gene therapy is to alter the tumor or the patient such that the cancer can be eliminated more easily. Many types of gene therapy have been tried. At The Toronto Hospital we have used a virus to transport a gene (IL2) into the prostate before radical surgery in patients who have a likelihood of failing surgery. One injection in the prostate is given 4 weeks before surgery. Early results suggest that this treatment may stimulate the body to kill small amounts of cancer cells that may have escaped from the prostate. One hopes that this or other treatments like this might convert a failed operation into a successful treatment.