A method of comparing differences in tumour growth rates applied to a study of the increasing growth capacity of mouse carcinomata.

A method of comparing differences in growth rates of tumours in small groups of animals is described. A common slope can be fitted to the growth curves of a given tumour in a group of isogeneic animals. Differences between growth potentials can be demonstrated by comparing the common slope for a given tumour against that of another tumour (or the same tumour at a later stage of development).A highly significant difference is shown between the growth potential of an A-strain mammary carcinoma after 7 or after 28 days' growth in isogeneic animals. Since this increase in autonomy is reflected in the tumour's subsequent growth rate in secondary hosts, it is suggested that it involves adaptation of the tumour rather than progressive immunodepression of the primary host.