ABSTRACT
BACKGROUND/AIMS: Electrochemotherapy, which uses two parallel electrodes for delivery of electric pulses, may be useful for treatment of tumor nodules. However, in clinical fields, tumors that are larger than the distance between the two electrodes are frequently observed, and it would be difficult in such cases to deliver electric pulses to the tumor. This study was done to define how host antitumor immunity is generated by repeated electrochemotherapy treatments, and whether it is associated with regression of even large tumor nodules. METHODOLOGY: Balb/c mice and Balb/c nude mice were inoculated subcutaneously with colon 26. Electrochemotherapy using bleomycin and electroporation (CUY21) was administered as a treatment for tumor nodules that were larger than the distance between the electrodes. RESULTS: In Balb/c mice, growth of large tumors at the start of treatment is not inhibited by a single electrochemotherapy treatment. However, complete tumor regression was obtained through repeated electrochemotherapy treatments. No tumor cure was observed among Balb/c nude mice under the same therapeutic conditions. Inflammatory cells were accumulated in the tumor tissue seven days after the third electrochemotherapy treatment. CONCLUSIONS: Repeated electrochemotherapy is a promising treatment, even for large tumors, such as are usually encountered in clinical practice, by generating T-cell dependent, antitumor immunity.