Delayed tumors of mice immunized against the ehrlich ascites tumor

It was found that delayed tumors appear in more than 60% of mice which had if been immunized against the Ehrlich ascites tumor. The animals had been immunized as young adults and as early as 9 months later—when they are approximately 1 year old—adenocarcinomata begins to appear in the lungs and other viscera as well as in the subcutaneous tissue and muscle. Some of these tumors simulate mammary tissue. It is believed that these delayed tumors are derived from progeny of the ascites cells rather than as spontaneous neoplasms. If this conclusion can be accepted, the tumor cell genome must have retained the “memory” of its breast‐like ancestor through hundreds of transplant generations in ascites form. In the immunized mice some of the injected cells must have been maintained under systemic control for a prolonged period, presumably until there is some regression in immune competency. After this time viable cells become distributed to sites where they can establish progressive tumors which differ histologically from the cells used for inoculation.