Differential Response to Heat of Metastatic and Non-Metastatic Rat Mammary Tumors

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Abstract
Interest in the use of heat for cancer treatment has increased markedly in recent years (1–4). Information has accumulated that such hyperthermia causes a selective and irreversible inhibition of metabolism in certain animal and human tumors correlated to cell killing (5–8). It remains uncertain, however, whether and under which conditions heat exerts a specific influence on tumor tissue since much of the information available is based on cells cultured in vitro. Nevertheless, the potential application of hyperthermia in the treatment of cancer is extremely attractive since, with the exception of systemic chemotherapy, which is a notoriously blunt weapon, regional and whole body hyperthermia are the only treatment modalities presently available which could address the major problem of human cancer: the metastatic lesion. It is not known, however, whether metastasizing tumors are more susceptible to hyperthermic treatment than non-metastasizing ones, although in vitro studies are consistent with this possibility (9). The metastatic capacities of a tumor cell are related to its surface (10, 11) and one of the major mechanisms of action of hyperthermia is thought to act via the membrane (12, 13). It, therefore, was of interest to compare the membrane properties and heat sensitivity in two closely related tumor strains of which one metastasizes whereas the other does not.