A method of treating cancerous tumors is presented herein. The method includes injecting an effective dose of a plasmid encoded for IL-12, B7-1 or IL-15 into a cancerous tumor and subsequently administering at least one high voltage, short duration pulse to the tumor. The electroporation pulses may be administered at at least 700V/cm for a duration of less than 1 millisecond. The intratumor treatments with electroporation may be administered in at least a two-treatment protocol with the time between treatments being about 7 days. The intratumor treatments with electroporation may be administered in a three-treatment protocol with a time of four days between the first and second treatments and a time of three days between the second and third treatments. It was found that the intratumor treatments using electroporation not only resulted in tumor regression but also induced an immune memory response which prevented the formation of new tumors.