Table 2.

Effect of estradiol (E) plus progesterone (P) treatment on MNU-induced mammary carcinogenesis

Treatment	Mammary cancer incidence	Percent of rats with mammary cancer	Average number of cancers per rat
Control	18/20	90	2.3  ±  0.4
30 mg of E plus 30 mg of P*	1/11§	9	0.1  ±  0.1§
Control	9/9	100	2.8  ±  0.1
30 mg of E plus 30 mg of P*	5/10‡	50	0.6  ±  0.2§
Control	9/9	100	2.8  ±  0.5
30 mg of E plus 30 mg of P*	0/8	0	0§
Control	10/10	100	2.8  ±  0.6
30 mg of E plus 30 mg of P†	1/9	11	0.1  ±  0.1§
Control	9/9	100	2.7  ±  0.5
200 μg of E plus 30 mg of P*	1/10§	10	0.1  ±  0.1§

Rats were treated with MNU at 7 weeks of age. 

^*Rats treated 2 weeks later with E plus P for 3 weeks. 

^†Rats treated 4 weeks later with E plus P for 3 weeks. 

^‡P = 0.05 compared to control. 

^§P < 0.005 compared to control.