Inhibition of Lewis lung tumor growth and metastasis by Ehrlich ascites tumor growing in the same host.

A double tumor model (3LL and EAT) was established in C57BL/6 mice. The primary 3LL tumor was growth-inhibited by EAT inoculated into the same host. Growth inhibition of the 3LL primary tumor depended on the number of EAT cells injected. Inhibition of the growth of the primary 3LL tumor was also observed after injection of the optimal number (10(7)) of EAT cells 24 h to 7 days before or after inoculation of 3LL cells. In contrast, metastasis of the 3LL tumor was only inhibited after simultaneous inoculation of 3LL and ETA cells. Moreover, EAT cells inhibited the growth of preformed 3LL-derived metastases after resection of the primary 3LL tumor. Although the EAT-induced stimulation of a host defense system is not excluded, the results are consisted with the continued release of growth inhibition factors from EAT cells acting on 3LL cells in the primary tumor and in lung metastases.