Prenatal Exposure to Diethylstilbestrol: Ovarian-Independent Growth of Mammary Tumors Induced 7,12-Dimethylbenz[a]anthracene

The effects of ovariectomy on the growth of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors were investigated after rats had been exposed prenatally to diethylstilbestrol (DES). Pregnant rats were inoculated with either DES (total dose: 1.2 μg) in sesame oil or with the vehicle alone on days 10 and 13 of gestation. Female offspring were given 2 gastric intubations of DMBA (10 mg each) 1 week apart beginning at 50±1 days of age. When the average diameter of a mammary tumor exceeded 2 em, the animal was ovariectomized. The initial response of most tumors in both the DES-exposed and control groups to ovariectomy was size regression. The growth of 7 tumors that arose soon after DMBA treatment in each group was studied for 12-20 weeks after ovariectomy. Whereas only 1 tumor from the control group resumed active growth after the initial regression period, 6 tumors in the DES-exposed group overcame the initial effects of ovariectomy and began to grow again. Thus ovariectomy appeared to be less effective in producing sustained control of growth in DMBA-induced mammary tumors in rats exposed prenatally to DES.