Prevention of rat colon cancer metastases by perioperative immunostimulation.

Major intra-abdominal operations result in profound immunodepression. In addition, manipulation of malignant tumors may release tumor cells into the systemic and portal circulations. The additive effects of immunodepression and tumor cell release may enhance the metastatic potential of tumors. Perioperative correction of immune depression by levamisole can restore lymphocyte proliferation levels in rats. We have developed a model in which rat colon carcinoma cells transplanted into the portal venous system consistently induce hepatic metastases by 4 weeks and death within 9 weeks. Rats pretreated with levamisole (4 mg/kg administered intraperitoneally) the day before and the day of tumor implantation developed fewer metastases (41% of animals treated with levamisole compared with 6% of animals not treated with levamisole had less than or equal to two metastases per liver). Twenty percent of the rats treated with levamisole developed no hepatic metastases. Comparison of median liver weights between the group treated with levamisole and the nontreated, tumor-bearing group was highly significant (p less than 0.005). We conclude that the perioperative period is critical for the implantation and growth of metastases and that perioperative immunostimulation may be a factor in decreasing the incidence of metastases. This model may have relevance to the adjuvant treatment of human colon cancer.