Combination Radiofrequency Ablation and Local Injection of the Immunostimulant Bacillus Calmette-Guerin Induces Antitumor Immunity in the Lung and at a Distant VX2 Tumor in a Rabbit Model

Purpose: To evaluate whether the combination of radiofrequency (RF) ablation and local injection of the immunostimulant Mycobacterium bovis bacillus Calmette Guerin (BCG) induces systemic antitumor immunity. Materials and Methods: Japanese White rabbits with lung and auricle VX2 tumors were randomized into three groups: control (n = 8; no treatment), RF ablation only (n = 8; RF ablation to the lung tumor), and RF ablation with local BCG injection into the lung tumor (n = 8). Treatments were performed 1 week after tumor implantation. Survival was evaluated with Kaplan Meier method and log-rank test. Weekly mean volume and specific growth rate (SGR) of auricle tumors were calculated, and comparisons were made by Mann Whitney test. Results: Median survival of control, RF-only, and RF/BCG groups were 23, 41.5, and 103.5 days, respectively. Survival was significantly prolonged in the RF-only and RF/BCG groups compared with the control group (P=.034 and P =.003, respectively), but no significant difference was found between the RF-only and RF/BCG groups (P=.279). Only in the RF/BCG group was mean auricle tumor volume decreased 5 weeks after implantation. No significant difference in SGR was found between the control and RF-only groups (P=.959), but SGR in the RF/BCG group, was significantly lower than in the control group (P=.005). Conclusions: The combination of RF ablation and local injection of BCG resulted in distant tumor suppression compared with the control group, whereas RF ablation alone did not produce this effect. Therefore, the combination of RF ablation-and local injection of BCG may induce systemic antitumor immunity.