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Estrogen & Breast Cancer: Controversies and Risks You Aren't Told - M

Estrogen & Breast Cancer: Controversies and Risks You Aren't Told

Reviewed by Michael Hua, Pharm D
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When a woman enters an age when her natural hormones start to decline, most doctors today will recommend some type of hormone replacement therapy (HRT). As effective as this treatment is and as reliable the outcome may be, many women faced with the decision of undergoing HRT treatment are hesitant. Unfortunately, over the years there have been instances of conflicting information regarding hormone replacement and the risk of breast cancer. If you are a woman who is considering HRT and worried about inadvertently heightening your own risks of breast cancer, you may want to take a closer look.

Estrogen & Breast Cancer: Controversies and Risks You Aren't Told

The widespread misunderstanding is that all types of hormone replacement therapy are linked to a higher risk of breast cancer, but research shows otherwise. The actual risks of breast cancer are determined not by the fact that you are on HRT, but according to the type of hormone-replacement medications you are taking. In short, and it may come as a bit of a surprise, your risks are only heightened if you are taking synthetic hormones instead of natural, bioidentical hormones.

Synthetic vs Bioidentical Hormones

Synthetic and bioidentical hormones are both essentially man-created, but with one very important caveat. Synthetic hormones are created from chemicals that mimic some of the biological actions of human hormones, but they don't offer the same effectiveness and are not identical. Bioidentical hormones are synthesized from hormones found in plants. These plant-based hormones are exactly like those found in the natural human body and they function in much the same way.

Synthetic Hormones

  • Premarin (conjugated hormones)

  • Provera

  • Progestins

Bioidentical Hormones

  • Estradiol

  • Progesterone

  • Estriol

With HRT, the goal is to replace the hormone levels that may be lacking in your system. Therefore, bioidentical hormones offer the body hormone forms closer to what is missing; the hormones are easier used by the body for better effects.

What types of estrogen cause breast cancer?

Conjugated estrogens and synthetic estrogens have been linked to higher risks of breast cancer. Likewise, synthetic progesterone, like Provera, is linked to higher rates of breast cancer.

In all truth, the risks of breast cancer associated with HRT may not be as big as what even some physicians suggest they are. So, where did this misinformation begin? Much of the misunderstanding is related to bioidentical hormones being lumped together with synthetic hormones, specifically in regard to one large-scale study.

Throughout the 1960s, doctors prescribed estrogen therapy to millions of women with hormonal deficiencies. Back then, the medication used was Premarin—conjugated estrogens from horses. Conjugated estrogen actually made up 50 to 70 percent of the total content of the medication. By the 1970s, scientists had found that conjugated estrogens were associated with higher rates of endometrial cancer at a rate of fivefold higher than non-users. Therefore, doctors transitioned to adding other synthetic hormones like Provera and synthetic progestins to protect the endometrium. Unfortunately, over the next two decades, studies found that women taking the two synthetic hormones together experienced a 4-5X increased risk of developing breast cancer with 5-10 years of use, increased blood clots, and a 50% increase risk of heart disease in the first year.

In 2002, the Women's Health Initiative (WHI) tackled one of the largest preventative studies with more than 160,000 women. The research effort determined that women who took synthetic hormones had heightened risks of breast cancer after five years of use. The problem with the WHI study was this: Bioidentical estrogen and progesterone were lumped together with synthetic progesterone and equine-derived estrogen to determine risks. Upon closer examination, the women who were taking bioidentical estrogen only, who had undergone a hysterectomy, actually had a 21 percent decrease in instances of breast cancer.

For many years, doctors have referenced the WHI study when explaining breast cancer risks to women in need of HRT. The study truly bred severe confusion in the medical community and among women who could absolutely benefit from hormone therapy. Bioidentical hormones may actually be one of the best preventative strategies when it comes to breast cancer, and several studies have indicated this to be true:

1990 - The E3N Cohort Study of more than 80,000 women between 40 and 65 found that natural estradiol and progesterone did not heighten the risks of breast cancer, but synthetic progesterone increased risks by 69% with long-term use and 36% in short-term use.

2008 - A Danish study of 698,098 women found that females that were given cyclical HRT made up of bioidentical estrogen and progesterone for 10 years had no increased risk of breast cancer

2013 - The Kronos Early Estrogen Prevention Study (KEEPS) of 727 women found that low-dose estradiol and cyclic progesterone did not increase rates of breast or endometrial cancer at all

While the debate is still ongoing, numerous medical researchers have pointed out that HRT should remain the primary standard of care for women during menopause.

To have a greater understanding of how risks are determined with any form of medicinal therapy, you must understand relative risk versus absolute risk. Relative risk is considered a measure of the risk of something taking place in one group compared to the risk of the same thing happening in a different group. For instance, a relative risk may be used to explain how women who smoke have a greater chance of developing breast cancer compared to (relative to) women who don't smoke.

Absolute risk is more absolute—you have a straightforward risk of developing a disease no matter what other factors may be involved. For example, one in every eight women will develop breast cancer in their lives.

So, what is the biggest risk for developing breast cancer? Let's break the risks down by absolute versus relative risks for a closer look.

Absolute Risk of Breast Cancer by Age

The overall lifetime risk for women to develop breast cancer varies by age. Here is a look at how absolute risks of breast cancer can change depending on your age.

  • 20 yo - 1 in 1,429

  • 30 yo - 1 in 208

  • 40 yo - 1 in 65

  • 50 yo - 1 in 42

  • 60 yo - 1 in 27

  • 70 yo - 1 in 25

  • 80 yo - 1 in 33

Relative Risk for Breast Cancer

Relative risks are the risks that may not necessarily apply to all women, but they are just as important to consider when making decisions about your health. While not exhaustive, here is a brief overview of some of the relative risks that may heighten the chances you will develop breast cancer as a woman.

Highest Relative Risk

  • Dense breast tissue

  • 2 or more immediate relatives were diagnosed with breast cancer early in life

  • Inherited gene mutations (PALB2, CHEK2, and BRCA)

  • Personal history of breast cancer by age 40

  • Over the age of 65

Medium Relative Risk

  • One immediate relative was diagnosed with breast cancer

  • Sedentary lifestyle

  • Prior high-dose radiation therapy to chest area

  • First pregnancy over the age of 40

  • Personal history of breast cancer over the age of 40

Some Relative Risk

  • Alcohol use before pregnancy

  • First period before the age of 12

  • Never breastfeeding

  • Long-term use of HRT with synthetic progestins

  • Tobacco use

  • Menopause beyond the age of 55

  • Personal history of reproductive or colon cancer

More and more prescribers have actually transitioned to bioidentical hormone replacement therapy (BHRT) for patients, making this the modern standard of care for women experiencing hormone decline due to menopause. However, some data actually shows that bioidentical hormones may offer both anti-cancer and protective advantages for the organs in the female body. So, could BHRT actually reduce the risks of breast cancer? Maybe, especially through secondary means.

Several consequences of low hormone levels or lacking HRT can heighten the risks of breast cancer all on their own. Insomnia and sleep disturbance, for example, is common with menopause. Studies suggest that women with poor quality sleep are more likely to develop more aggressive forms of breast cancer. Even more disturbing, prescription sleeping pills, often prescribed to menopausal women to help them sleep, are also linked to heightened risks of cancer.

Likewise, stress raises the risk of breast cancer, increases metastasis, and increases the possibility of breast cancer recurrence. And, depression increases the risk of breast cancer by 380%. Estrogen improves natural serotonin levels, and prescription SSRIs (selective serotonin reuptake inhibitors) may be linked to higher rates of cancer.

Does estrogen replacement actually directly lower your risks of breast cancer? Research has shown that estrogen-only HRT actually reduced breast cancer risks by about 20 percent. Also, those risk reductions seemed to carry over for a few years after treatment had stopped.

Even though misinformation about hormone replacement has been rife for a lot of years, new studies are consistently showing that the benefits of HRT far outweigh the risks involved. Women who need hormone replacement should not be misled by the idea that all replacement hormones are the same because they can be far different and all carry different risks.

If you suspect you have low hormone levels due to menopause, talk to a hormone specialist openly about your options. Each woman's situation can vary, but bioidentical hormone replacement can target so many of those unwanted symptoms associated with declining estrogen. There is no reason to delay treatment that could help due to the misconception that you are putting yourself at risk. Plus, BHRT may directly and inadvertently lower your risks of developing breast cancer.

To find out more about BHRT or risks of breast cancer associated with HRT, reach out to one of our friendly staff members at Harbor Compounding Pharmacy for advice.

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