The effect of hyperthermia 42.5 degrees C on the incorporation of 3H-thymidine into the DNA of solid tumours in childhood.

Supranormal temperatures inhibit selectively the growth of malignant cells more than that of normal cells. The autoradiographic determination of the 3H-thymidine-labelling-index (LI) in vitro is a suitable method for the examination of thermosensitivity of individual human tumours. 44 solid tumours of children (Wilms' tumours, neuroblastomas, osteogenic sarcomas, non-Hodgkin-Lymphomas and other tumours) were studied by the temperatures 37.5 and 42.5 degrees C/120 min, with this method. 90% of the histologically undifferentiated tumours showed a highly significant inhibition of the 3H-thymidine incorporation between 28.6 and 79.9% with an average of 51.1%. In 4 histologically mature tumours (carcinoma of the adrenal cortex, malignant hepatoblastoma, fibrosarcoma, hamartoblastoma) no significant decrease of the LI was present. The inhibition of incorporation with hyperthermia cannot be correlated with the primary magnitude of the LI with normothermia. In 1 neuroblastoma a 75% rise of the LI was found possibly due to exogenic caused thermotolerance. The individuality of the reaction towards heat may contribute to the biological characterization of tumours.