EFFECT OF HYPERTHERMIA 42.5-DEGREES-C 120 MIN ON 3H-THYMIDINE INCORPORATION IN DIFFERENT TISSUE-COMPONENTS OF WILMS-TUMORS - AN IN-VITRO STUDY

Background Survival rates of Wilms' tumors are correlated to tumor his tology. Clinical studies and histological investigations have shown th at different histological tumor components of Wilms' tumors also revea l different sensitivities to cytostatic agents and ionizing radiation. The aim of this study is to examine the effect of hyperthermia to Wil ms' tumors, generally, and to the different tumor tissues composing ne phroblastomas. Material and method The 3H-thymidine labelling indices (LI) of 23 Wilms' tumors and one renal rhabdomyosarcoma were studied b y an autoradiographic in vitro method at temperatures of 37.5 degrees C/120 min and 42.5 degrees C/120 min. The LI of each tumor was measure d and likewise the LI of all histological tumor components defining st andard risk and high risk. The effect of hyperthermia was calculated a s the percentage of inhibition of 3H-thymidine incorporation. Results Labelling indices between 22.4% and 46.3% (mean 33.2%) characterized W ilms' tumors as highly malignant and fast growing tumors. The LI of Wi lms' tumors of standard risk and high risk did not differ significantl y (33.8% vs. 30.4%). Also, epithelium and blastema of the same groups showed comparable high LI of 31.4% and 34.4%,respectively, and of 32.1 % and 26.8%, respective ly. The LI of stroma was significantly lower ( 11.9% and 10.9%). The mean LI of fetal-like rhabdomyoblastic cell elem ents of ten tumors was 24.5%. These tumor cells revealed a significant ly higher LI than rhabdomyosarcomatous cells in one Wilms' tumor and o ne renal rhabdomyosarcoma (10.2% and 9.0%, respectively). The LI of an aplastic structures of one tumor was more than twice as high as the LI of surrounding tumor tissue. In vitro hyperthermia significantly inhi bited 3H-thymidine incorporation into all nephroblastomas. Inhibition ranged between 13.7% and 84.6%, at an average of 47.3%. Four high risk tumors, as well as the single anaplastic and rhabdomyosarcomatous cel ls responded significantly stronger to heat than standard risk tumors (mean inhibition of 62.6% vs. 42.1%). Hyperthermia was more effective for blastema compared to epithelium and stroma. There was no correlati on between the effect of hyperthermia and the amount of the 3H-thymidi ne LI at normothermia. Conclusion The tremendous inhibition of DNA syn thesis by hyperthermia particularly in high risk tumors and highly mal ignant tumor components is of clinical interest for children with Wilm s' tumors resistant to conventional therapy.