Autoradiographic study on the effect of hyperthermia (42.5 degrees C) on the proliferation kinetics of solid tumors in children.

Supranormal temperatures between 40 and 43 degrees C are not necessarily lethal to tumor cells, but lead to characteristic changes of the cell cycle. The parameters of the proliferation kinetics were studied in 35 solid tumors of children at a temperature of 42.5 degrees C with an autoradiographic in vitro method, in comparison to normothermia: 9 Wilms' tumors, 10 neuroblastomas, 8 osteogenic and soft tissue sarcomas, 6 non-Hodgkin-lymphomas, and 3 other tumors. 28 tumors showed significant prolongation of DNA synthesis times by an average factor of 1.27 (1.10--3.12). Mitosis times undergo an average prolongation by the factor 2.75 (1.07--8.87). Together with significant decrease of the 3H-thymidine labeling index the prolongation of the cell cycle time amounts to an average of 2.67 (1.05--8.30). The cause of the changes of the cell cycle are discussed. Probably, the heat sensitivity of tumors is correlated with the proliferation rate and with the degree of histological differentiation; but this cannot be confirmed statistically due to the small number of cases. 2 cases responded with a decrease of the duration of the cell cycle; in one case this was probably due to an exogenic thermotolerance. The changes of the cell cycle are of a particular importance for the therapeutic combination with radio- or chemotherapy. These relations are discussed.