Response to heat treatment (42.5 degrees C) in vivo and in vitro of five human melanoma xenografts.

The response to heat (42.5 degrees C) of five human melanoma xenografts was studied. Tumours grown subcutaneously in the hind leg of athymic mice were heated in a water-bath and specific growth delay was used as a measure of response. In other experiments, cells from the same xenografts were heated in vitro and the colony-forming ability was assayed in soft agar. The slopes of the in-vivo dose-response curves (specific growth delay versus heating time) varied within a factor of about three among the five melanomas. The Do values of the in-vitro heat survival curves ranged from 44 +/- 3 to 123 +/- 15 min. The response to heat in vivo was not positively correlated with the tumour volume-doubling time, the growth fraction, the cell loss factor or the intrinsic heat sensitivity of the tumour cells, i.e., the Do values of the in vitro heat survival curves. If the results obtained in the present work are representative for clinical practice, they indicate that the response to heat may vary considerably among tumours in different patients. This variability can probably not be predicted from measurements of cytokinetic parameters of the tumours. The lack of correlation between the response to heat in vivo and in vitro demonstrates that extrapolations of results from studies in vitro to tumours are highly speculative and, when attempted, should be executed only with extreme caution.