Perturbation of the growth kinetics of C3H mouse mammary carcinoma by irradiation of tumour and host and by attempted pre-immunization of host.

The kinetics of development and subsequent growth of a C3H mouse mammary tumour after implantation of 10(6) cells was quantified by observation and statistical analysis of latent period and growth rate for different categories of tumour. These comprised control tumours, tumours recurring after large single doses of X-rays alone and in combination with misonidazole, tumours developing from cells implanted both outside and within the sites of tumours previously cured by irradiation, tumours developing from cells implanted in heavily irradiated skin, and tumours developing from cells taken from tumours recurring after irradiation and re-implanted in untreated skin. The kinetics of development and growth of tumours in host animals previously treated by i.p. injection of killed tumour cells was also quantified. The results confirm that tumour development and growth is significantly perturbed by irradiation of host tissues both before and after tumour transplantation, and that this perturbation involves an extended latent period, a slower average rate of growth and a less uniform pattern of growth. These effects result from localized radiation damage to host tissues, are not attributable to residual damage to irradiated tumour cells, and are not markedly dose-dependent within the dose range 25--80 Gy. These results are consistent with the complete sterilization of host endothelial cells by doses of 25 or more. In marked contrast to the growth-slowing effect of irradiation, the treatment of host animals by previous injection of radiation-killed tumour cells led to a reduced latent period and a faster average rate of growth.