Local control and distant metastases in primary canine malignant melanomas treated with hyperthermia and/or radiotherapy

Forty-three dogs with primary malignant melanoma were randomized to receive radiotherapy alone (XRT) or hyperthermia plus radiotherapy (δ + XRT). Tumour responses were analysed in terms of complete response rates, rate of one year disease free survival and the incidence and time to develop distant metastasis. The frequency of complete responses (CR) was greater with adjuvant heat (76 per cent vs 21 per cent for XRT; P = 0.001). A trend towards an improvement in one year disease free survival was observed with δ + XRT (23.8 per cent) as compared with XRT (7.7 per cent), but the difference was not statistically significant. The frequency of distant metastases was not different between the two treatments. Descriptors of intratumoural temperatures achieved during therapy indicated that higher CR rates could be achieved with higher minima. When minima were less than and greater than 20 Equivalent minutes at 43°C (Eq43) the CR rates were 64 and 90 per cent, respectively. One year disease free survival rates and frequencies of distant metastases seemed to be correlated with the intratumoural temperatures as well. This was reflected in analyses examining temperature minima and maxima. Examination of patterns of failure suggested that the most plausible explanation for the correlation between intratumoural temperature and metastases was the high local failure rate (70 per in the heated group). The results of this study emphasize the need for further investigation of the influence of local hyperthermia as a part of curative therapy on the frequency of distant metastases.