The relationship between the unmodified initial tissue pH of human tumours and the response to combined radiotherapy and local hyperthermia treatment

Abstract

The relationship between unmodified tumour pH before treatment and tumour response was investigated in patients receiving combined radiotherapy and local hyperthermia treatment. Tumour pH showed a statistically significant positive correlation with the response rate (Spearman correlation coefficient 0.31, n = 50, 2P < 0.05). The mean pH of tumours showing a complete response (CR) was significantly higher than that of tumours showing a partial response (PR) as well as those showing no change (NC). As the means of the PR and NC groups were not significantly different from each other, these groups were combined for further analysis. The pH of the CR group was also significantly different from that of the NC + PR group (CR: 7.36 ± 0.05, median 7.36, n = 18, NC + PR: 7.16 ± 0.06, median 7.21, n = 32); Mann-Whitney test: 2P < 0.05). Stratification of the data with respect to radiotherapy dose, hyperthermia dose or tumour volume showed that these factors were not associated with tumour pH to such a degree that they might have seriously biased the results. The results suggest that enhancement of the cytotoxic effects of hyperthermia by low pH known from experiments with cell cultures is not observed in tumours which are treated with radiotherapy and hyperthermia, and that even the converse may occur. The reasons for this are discussed at length and it is suggested that sudden modification of the tumour pH directly prior to or during treatment is imperative to obtain any sensitizing effect.