Effect of estrogens on dmba induced breast tumors

Evidence is presented for the anti-carcinogenic activity of estriol when this hormone is administered to 50–55 day old SD rats prior to treatment with DMBA. In control and estradiol treated animals, 85–100% of animals developed breast tumors regardless of dose of steroid. Low doses of estriol (1 μg/day) offered some protection against tumorigenesis but at levels exceeding 10μg/day only 20–35% of animals developed tumors even when observed for 180 days following DMBA ingestion. Furthermore, the mean time for tumor production is greatly increased in the presence of E₃. Short term (2 weeks) administration offered no protection against tumor formation, suggesting that the effect of estriol probably relates to the promotion stage of tumorigenesis.