In a study of over 80,000 postmenopausal women, the following breast cancer risk was observed:
- Women who used estrogen only were found to have a 29% increased risk of breast cancer compared to women who had never used Hormone Replacement Therapy (HRT)
- Women who used estrogen plus a synthetic progestin were found to have a 69% increased risk of breast cancer compared to women who had never used HRT
- Women who used estrogen plus progesterone were found to have no increased risk for breast cancer
“These findings suggest that the choice of the progestagen component in combined HRT is of importance regarding breast cancer risk; it could be preferable to use progesterone.” (Progestagen – also spelled progestogen – is the class of hormones that includes progesterone and progestins.)
Breast Cancer Res Treat. 2008; 107(1):103-111.
The Developmental Endocrinology Branch, National Institutes of Health, had previously shown that the addition of natural testosterone (not METHYLtestosterone) to conventional hormone therapy for postmenopausal women does not increase and may indeed reduce the risk of breast cancer.
Menopause. 2004 Sep-Oct;11(5):531-5.
A study of the influence of topically administered estradiol and progesterone on human breast tissue concluded that progesterone administration decreases estrogen-induced breast cell proliferation by 400%.
Fertil Steril. 1995;63(4): 785-791.