A comparison of cryodestruction with excision or infarction of an implanted tumor in rat liver

In this study a malignant tumor was implanted in rat livers and treated by infarction, excision, or cryodestruction. Survival and the pattern of metastases was studied in each group. Walker carcinomas were induced by the inoculation of a tumor cell suspension into the livers of male Sprague-Dawley rats. Ten days after inoculation a solitary tumor had formed. This was treated by (i) mobilization of the tumor-bearing lobe (controls); (ii) ischemic infarction by ligation of the vascular pedicle to the lobe; (iii) excision of the tumor-bearing lobe; or (iv) cryodestruction of the tumor and surrounding liver using a clinical liquid nitrogen probe. A double freeze/thaw cycle to - 180 degrees C at a mean cooling rate of 94 degrees C/min was performed. Autopsy was performed at death or after 110 days, when the experiment was terminated. In general, deaths within 5 weeks of treatment were from recurrent tumor growth in the liver and, after this time, from metastatic disease. A statistically significant increase in survival was noted in the cryotherapy group when compared with the other treatment groups (P less than 0.01 logrank ) and controls (P less than 0.001 logrank ). No real difference in local tumor control was noted between the groups. The improved survival in the cryotherapy group was attributed to a statistically significant reduction in deaths from metastatic disease (P less than 0.05 Chi-square). This finding may be related to an immunological response and warrants further study.