Table 3.

Effect of estrogen metabolites on mammary carcinogenesis

Treatment	Duration	Mammary cancer incidence	Rats with mammary cancer (%)	Average number of cancers per rat
Control	3 weeks	9/12	75	1.3 ± 0.5
2 mg 2-hydroxy estradiol	3 weeks	8/10	80	1.4 ± 0.3
2 mg 2-hydroxy estradiol + 30 mg progesterone	3 weeks	6/10	60	1.5 ± 0.5
2 mg 2-methoxy estradiol	3 weeks	6/10	60	0.7 ± 0.2
2 mg 2-methoxy estradiol + 30 mg progesterone	3 weeks	3/10*	30	0.4 ± 0.2

Rats were treated with N-methyl-N-nitrosourea at 7 weeks of age. At 9 weeks of age, the rats were treated with hormones for 3 weeks. Control rats received empty silastic capsules. *P < 0.05 compared with controls.