Dose dependence of immunopotentiation and tumor regression induced by levamisole.

Breast cancer was induced in female Sprague-Dawley rats by 7,12-dimethylbenz(a)anthracene. Once tumors had become established, they were treated with varying doses of the immunopotentiating drug, levamisole. Tumor growth was measured in the various dosage groups, and at 6 months after tumor induction the animals were sacrificed. Their immunological competence at this time was measured by the mitogen responses of splenic lymphocytes. Untreated animals with breast cancer were found to be immunosuppressed compared to normal animals. The drug levamisole resulted in immunopotentiation, but at high doses it was immunosuppressive. Tumor regression was observed at doses that resulted in immunopotentiation, but not at high doses. There was a significant correlation between immune competence and tumor regression. It is concluded that levamisole can cause regression of breast cancer in the rat but that this effect is critically dependent on the dose of the drug; these observations confirm previous studies carried out on human cells in vitro. It is recommended that high doses of the drug be avoided in human clinical trials and that the patients who receive this drug should have their immune responses carefully monitored.