Early Growth of Experimental Lung Metastasis in Mouse

A radiobiological method was developed to measure the initial growth of clonogenic tumor cells metastasizing to the lung. The thoraxes of mice were externally irradiated by g rays after an intravenous transplantation of syngeneic fibrosarcoma cells. The lung colonies which developed 11 days after irradiation were counted and provided surviving fractions. Survival curves moved downward when the time interval between transplantation and radiation was delayed from 1 to 21 hr, but shifted upward at 48 hr or later. Survival ratios at given doses and the extrapolation number of survival curves fitted to multi-target model were calculated, and plotted against time after the intravenous transplantation. Doubling times of 13.3 and 13.1 hr were obtained by use of the survival ratio and of the extrapolation number, respectively. This method is useful to measure the growth dynamics of clonogenic tumor cells at the site of a metastasized organ.