Effective hepatic cryoablation: does it enhance tumor dissemination?

This experimental study was designed to investigate the risk of tumor dissemination by hepatic cryosurgery and to determine the final subzero temperature required for effective hepatic tumor cryoablation. Although cryosurgery is now one of the established modalities for the treatment of some liver tumors and has been used for two decades, controversy remains regarding the final subzero temperature needed to destroy tumor masses. One experimental report has indicated that hepatic cryosurgery may enhance tumor dissemination. For this study, rat hepatic tumors were produced by direct injection of rat colonic carcinoma cells (DHD/K12/TRb). The control untreated animals (n = 12) were sacrificed after induction of liver tumors at 4 and 6 weeks. The animals in the treatment group (n = 16) underwent cryosurgery 2 weeks after tumor induction and were allowed to recover before sacrifice 2 and 4 weeks later. Pulmonary metastases were identified in 9 of 12 (75%) control animals at postmortem examination (2 and 6 weeks after tumor inoculation) and in 6 of 16 (38%) rats in the treatment group at sacrifice 2 and 4 weeks after cryosurgery (p = 0.11, Fisher's test for unpaired analysis). Peritoneal deposits were observed in 5 of 12 (42%) control animals at postmortem examination and in 8 of 16 (50%) of the treated animals at the time of cryosurgery (p = 0.95, Fisher's test for unpaired analysis). Two other study animals developed deposits after cryosurgery. The prevalence of peritoneal deposits in the study group was not altered by cryosurgery (p = 0.5, McNemar's test for paired analysis). The importance of the final subzero temperature at the edge of the iceball during tumor ablation by cryosurgery was confirmed by the histologic findings. Complete ablation with no residual viable tumor was obtained only when the subzero temperature had reached -38 degrees C or below. The results of this study do not support the suggestion that hepatic cryosurgery enhances tumor dissemination. The findings also confirm that a subzero temperature at the edge of the iceball of -38 degrees C or lower is necessary to ensure complete ablation of tumor.