Growth and regression of the Rous sarcoma as a function of the age of the host.

Although there is extensive information con cerning regression of the Rous sarcoma, the sub ject was restudied by us when it became clear that regression of the tumor was closely conditioned by the age factor—a factor which, as previously shown (11, 12), exerts such important effects on the tumor as masking its causative virus and sup pressing its transmissibility by cells and its power to induce métastases.This paper reports the re sults of the study, together with other pertinent data. Regression followed by varying degrees of im munity in several transplanted chicken tumors has been observed to occur spontaneously (2, 3, 5-7, 9, 16-19) or as a result of various treatments (4, 14, 15). No such regressions have been noted in young hosts, Gye and Purdy (13) observing only one case out of 6,000 young chickens bearing tumors. It has also been reported (1, 8, 14) that extirpation of a growing tumor is not followed by immunity.