Menopause Hormone Therapy: Not Proven to Increase Breast Cancer Risk

A photo of a sheet of menopause hormone treatment pills beside a cancerous cell, depicting that the treatment course is not linked to increased risk for breast cancer

Many women are fearful of menopause hormone treatment (MHT) believing that they cause breast cancer. This is not correct.

In 2002, there was a large study called the Women’s Health Initiative. The goal of this study was to determine if hormone therapy reduced the risk of cardiovascular disease. The study was intended to last 8 years. As the end point was cardiovascular disease, an older population was chosen (average age 63). 

The study, however, was prematurely stopped after 5 years as the investigators reported an increased risk of breast cancer in the estrogen/progestin arm of the study. Once the study was reported on, the prescriptions for hormone therapy declined by 79%.

There are some noteworthy flaws with the study that fail to establish solid evidence of MHT’s links to breast cancer risk. Let’s discuss this below.

Flawed Study Designs and Inconclusive Findings

 A woman in her late 50s happily receiving a sheet of menopause hormone treatment pills from her doctor

First, the study was not designed to investigate the risk of hormones for breast cancer so therefore the groups were not matched based on breast cancer risks. Remember, the original question of the study was about cardiovascular risk. So therefore, it is difficult to interpret data regarding breast cancer. 

Subsequent reanalysis of the data has shown that the placebo group (those who did not get any hormones and were therefore the control group) actually had a lower than average risk of breast cancer because many of those women had previously been on hormone therapy. So ultimately, there was not actually an increased risk in the estrogen plus progestin arm of the study.

The estrogen only arm of the study (for those women who had a prior hysterectomy) showed a trend towards decreased breast cancer risk and a statistically significant reduction in breast cancer mortality.

Furthermore, the formulations used in that study are not typical hormones that we use today.  They used conjugated equine estrogen and medroxyprogesterone acetate. There are now FDA approved bioidentical medications (similar to what the body produces) that are typically prescribed first line.

The True Impact of Hormonal Therapy

We have also learned that when you start hormones matters. For those women who start within 10 years of their final menstrual period, the benefits generally outweigh the risks. Hormone therapy is associated with a:

  • Reduced all cause mortality (meaning anything that can cause death)
  • Reduced risk of osteoporosis
  • Reduced risk of colon cancer
  • Reduced risk of type 2 diabetes
  • Reduced risk of insulin resistance

Transdermal estrogen (through the skin – gel or patch) has a neutral effect on the risk of blood clots. Oral estrogen does increase the risk of blood clots.

There is also data to support that hormones, when started within 10 years of the final menstrual period, improve cardiovascular health. This was a Danish study (Danish Osteoporosis Prevention study) that found that women taking hormone therapy experienced significantly lower rates of heart attack, heart failure and death. This study used estradiol (bioidentical estrogen) as compared to conjugated equine estrogen. The Danish study was terminated early as the WHI findings were released.  

Estrogen (specifically estradiol that our bodies make) plays an important role in maintaining the health of our blood vessels. Estrogen improves the ability of the blood vessels to relax and dilate. Estrogen has anti-inflammatory and antioxidant effects.  

There is also data to suggest that estrogen plays a vital role in cognition and brain health.

Current estimates are that 5 to 10% of women use menopausal hormone therapy. Classic symptoms (hot flashes/night sweats) are present in 75-80% of women. The symptoms last on average 5-7 years. All women will experience bone loss (10% in the first 5 years post menopause) and most women (80-90%) will experience changes in the vulva and vagina (dryness/discomfort with intercourse/urinary symptoms).

You have a choice – this information is intended to help you make the best choice for yourself. Armed with the most updated knowledge on menopause treatment, our specialists at Northside/Northpoint OB-GYN are always ready to give you the answers you’re looking for.

Additional resources:

NY times article which was then read as a podcast – “Women have been misled about menopause”

Article in Ms Magazine which was a response to a series of articles published in the medical journal Lancet

Website for the menopause society

Website for the SWAN study (study of women across the nation)

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