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Table 2 Effect of synthetic estrogens and progestins on mammary carcinogenesis

From: Prevention of mammary carcinogenesis by short-term estrogen and progestin treatments

Treatment Duration Mammary cancer incidence Rats with mammary cancer (%) Average number of cancers per rat
Control 3 weeks 9/12 75 1.5 ± 0.3
100 μg eE + 30 mg megesterol 3 weeks 3/13* 23 0.3 ± 0.2*
30 mg tamoxifen + 30 mg progesterone 3 weeks 7/12 58 0.9 ± 0.3
100 μg eE + 30 mg megesterol 1 week 5/13 38 0.4 ± 0.1*
100 μg eE + 30 mg norethindrone 1 week 3/12* 25 0.2 ± 0.1*
  1. 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 1 or 3 weeks. Control rats received empty silastic capsules. eE, 17α-ethynyl estradiol. *P < 0.05 compared with controls.