Enhanced thermal response of a rat sarcoma by Corynebacterium parvum

Corynebacterium parvum was investigated in the response of rat Mc7 sarcoma to local waterbath hyperthermia. Heat treatment of 1-1.5 cm3 foot tumors at 43 degrees C for 2 h resulted in complete regression of 71% of the tumors. The Mc7 cure was reduced to 31% when the tumors were heated at 43 degrees C for 1.5 h. C. parvum (700 micrograms, i.v.) when given 1-3 days before tumor heating at 43 degrees C for 1.5 h increased the host phagocytic activity, and the tumor regression from 31% to 65% (P less than 0.05). C. parvum by itself had no curative effect on the tumor, and it did not enhance the thermal response of normal rat foot to hyperthermia. These findings suggest that host response to tumor heating may be 'non-specific' in nature involving phagocytes of the reticulo-endothelial system.