Effect of pregnancy and nursing on the growth of metastases from N-nitroso-N-methylurea-induced mammary carcinomas.

Pregnancy increased the survival times of inbred BUF/N rats bearing occult metastasis of a mammary carcinoma at the time of conception. Nursing following delivery nullified the effect of pregnancy. The similarity of the controlled experimental data with the limited clinical observations is noted. An experimental model of rat mammary carcinoma has been described that possesses a highly metastasizing capacity and can be utilized to study the behavior of clinically silent metastasis.