The Development of Multiple Tumors in Tarred and Radiated Mice: Part II

Abstract

In an earlier paper (1) the preliminary results of a study of the effect of radiation on the subsequent development of tar tumors were given. The present paper deals with the final results of this experiment. As outlined previously, the experiment consisted of painting with a sample of coal tar of unknown carcinogenic power, the interscapular region of 139 albino mice, chosen from an inbred strain. This strain, called strain 3, developed by the biologist of the State Institute, Mr. Marsh, is a high-cancer strain, in which upwards of 80 per cent of the bred females develop spontaneous mammary cancer, while the unbred females have a cancer incidence which is slightly lower and somewhat retarded. The mice used in this experiment were unbred females and therefore belong in the latter group. The tar was applied twice weekly, one group receiving 8 applications, another 16 applications, and a third group 24 applications. Following the tarring, each large group was divided into two subgroups, one of which was radiated with heavy doses of gamma rays, while the other was held as a control group. Approximately six months after cessation of tarring, when the mice were ten to eleven months old, all of the animals still alive (103 in number), irrespective of the grouping, showed widely distributed multiple tumors on the skin (Figs. 1–4). The location of these tumors bore no relation to the site painted; in fact, this site rarely showed any tumor formation. The widespread occurrence of the tumors is indicated by the fact that 26 separate and distinct nodules were counted on one animal.