Growth, cell proliferation and morphological alterations of a mouse mammary carcinoma after exposure to X-rays and hyperthermia.

A C57 mouse mammary carcinoma was irradiated with 10, 20 or 30 Gy of X-rays or heated to 43 degrees C for 30 min preceded or not by exposure to 10 Gy. Tumour growth, cell proliferation kinetics, induction of micronuclei and morphological changes in necrosis and vascular density were simultaneously determined. Treatment with radiation and/or hyperthermia produced only a delay in tumour growth of between 1 and 3.8 days. However, the effects of the treatments became more apparent when the amounts of muscle and necrosis were deducted from the originally measured tumour volume. Radiation-induced G2 block of the cells was observed at 12 h after irradiation alone. After the combined treatment, however, the G2 block was delayed beyond 12 h. Moreover, 24 h after the various treatments, the proportion of S-phase cells decreased considerably although the formation of micronuclei showed only a marginal increase. However, the ratio of S-phase cells to micronuclei was significantly reduced during this period. Whereas the amount of necrosis was markedly enhanced 5 days following treatment with 10 Gy plus heat, as well as after 30 Gy, no alterations in the density of small blood vessels could be observed during this period. These results clearly demonstrate that the apparent changes in tumour volume after X-rays and hyperthermia do not truly reflect the response of the constituent cells and that there are many other factors, for instance cell proliferation and morphological alterations, that influence the effects of radiation and hyperthermia on tumours.