HRT and Breast Cancer

The WHI study added to the evidence that at least some types of HRT are associated with an increased risk of breast cancer. Other studies have found an increased risk of breast cancer in women who take estrogen for 5 or more years, the risk rising with longer duration of HRT use. Use of a progestin along with estrogen in these studies did not seem to reduce that rising risk and may even have increased it.

In the WHI study, the combination of the progestin medroxyprogesterone acetate (MPA) with estrogen in a daily pill appears to be responsible for the increased risk of breast cancer. The estrogen-only (Premarin) arm of the study is continuing and has not yet found an increased risk of breast cancer in the women taking unopposed estrogen. To read the latest information about the WHI studies on HRT, its risks, benefits and side effects, visit the National Heart, Lung and Blood Institute's web site.

There is evidence that micronized progesterone and progestins have differing effects on breast tissue, and that the regimen used plays a role. For example, taking both estrogen and the progestin medroxyprogesterone acetate (MPA) every day (continuous combined regimen) is known to cause increased breast density and is associated with an increased risk of breast cancer. Regimens that involve taking estrogen daily and progestin or progesterone for only part of each month (cyclical combined regimen) are less likely to cause increased breast density. Micronized progesterone used cyclically may actually help protect against breast cancer.

More research is needed about the varying effects of different formulations, doses, and regimens of HRT on the breast.

For more information and resources about breast cancer, please see this page at ProjectAWARE.

Please read on...
	What Is Hormone Replacement Therapy (HRT) and Why Would I Need It?
	What Hormones Are Used in HRT? and How Is HRT Taken?
	About Estrogen
	About Progesterone
	Benefits, Risks and Side Effects of ERT, HRT, and NHRT
	HRT and Breast Cancer
NEXT:	Androgens, SERMs and Other Drugs for Menopause
	What Are Some Alternatives to Standard HRT?
	Resources and References

Page uploaded September 2002

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Progesterone FAQ

Synthetic Progestins and Natural Progesterone, Differences

Natural Progesterone, What Role in Women's Healthcare

Tamoxifen for Prevention of Breast Cancer

Testosterone and Its Benefits to Women

Testosterone's Impact on Postmenopausal Women...

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Typical HRT Products

Where to get Natural Hormones

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Alternative Remedies for Menopausal Symptoms

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Updated 09/29/2010