Effects of hyperthermia on primary and metastatic tumor growth and host immune response in rats.

A hot water bath was used to heat locally a metastasizing carcinoma in Wistar/Furth rats. Applying heat such that intratumor temperature is maintained at a mean value of 42.3 degrees for two 90-min sessions results in a decreased growth rate of the primary tumor as well as distant metastases. Heating the primary tumor for only one 90-min session or heating the leg contralateral to the tumor-bearing limb has no effect on the growth rate of either the primary tumor or metastases. Heat therapy has no detrimental effect on the spleen cell-mediated tumor immune response of rats as tested by an in vitro lymphocytotoxicity assay 1 day later. However, heating isolated spleen cells to similar temperatures in vitro reduces their capacity for in vitro tumor cell killing.