Hormone Replacement Therapy and Cancer


When I first started working in the pharmacy as a pharmacy technician, I remember hormone replacement therapies like Premarin (synthetic estrogen) and PremPro (synthetic estrogen and progesterone) were some of the fastest moving medications! We were constantly filling prescription after prescription- they were virtually flying off our shelves- it seemed that every postmenopausal woman was on this medication!

But a few years later, when I was in my first year of pharmacy school that all stopped. The Women’s Health Initiative study came out. This study reported that postmenopausal women who took synthetic hormone replacement therapy had higher rates of breast cancer and stroke compared to postmenopausal women who didn’t!

Overall, the study reported the following outcomes for postmenopausal women who took a combination estrogen/progestin product:

  • Increased risk of heart attack
  • Increased risk of stroke
  • Increased risk of blood clots
  • Increased risk of breast cancer
  • Reduced risk of colorectal cancer
  • Fewer fractures
  • No protection against mild cognitive impairment and increased risk of dementia (study included only women 65 and older)

For postmenopausal women who took an estrogen product only, the following outcomes were reported:

  • No difference in risk for heart attack
  • Increased risk of stroke
  • Increased risk of blood clots
  • Uncertain effect for breast cancer
  • No difference in risk for colorectal cancer
  • Reduced risk of fracture

Women everywhere, as well as their doctors and pharmacists, began panicking. At the pharmacy, we received phone call after phone call from concerned women who had been taking these medications for many years! Can you blame them? These women were following their doctors’ orders, only to find out that something they were told to do to make themselves healthier was potentially making them sicker! I felt awful for dispensing medications to them that could potentially increase their risks of cancer and heart disease and as a pharmacy intern, I was sure to counsel every woman who came in for a prescription for HRT to talk to her doctor about the latest study.

And so eventually, the Premarin prescriptions began to decrease, and the Premarin bottles, once displayed prominently in the middle of the pharmacy in our fast mover section sat on remote shelves in the back of the pharmacy collecting dust. This started back in 2002, and I worked at community pharmacies until the middle of 2008, when I started my public health career. During those six years in community pharmacy, I hardly saw prescriptions for these products dispensed.

However, there are obvious benefits to hormone replacement therapy (HRT) in postmenopausal women. HRT can dramatically ease the symptoms of menopause, such as dry skin, low libido, and hot flashes, making women feel so much better. And of course we know that as with most medications, the side effects are going to vary per individual and not every person will get every side effect. Health conditions and risk factors are also very much associated with genes and lifestyle. So for every woman that developed breast cancer after taking HRT for 10 years, 52 women didn’t…

According to the National Health Service in the UK: “It’s estimated that there will be an extra 19 cases of breast cancer for every 1,000 women taking combined HRT for 10 years. The risk continues to increase slightly the longer you take HRT, but returns to normal once you stop taking it.”

Thus some women continued to stay on HRT and decided to “take their chances.” Some of them sought out bioidentical hormones, with the hope that these types of hormones would be safer. But no one really knew if bioidentical hormones were any safer…

To be completely transparent, hormone replacement therapy is something that has made me very uncomfortable since my first year in pharmacy school. I knew that many women have benefitted from this type of therapy, but I also knew that others were harmed by it. This is true for many drugs, and that’s why health care professionals receive extensive training on the risks, benefits, and contraindications for various medications.

But there was so much confusion and controversy about hormone replacement therapy! And women felt worse when they came off of it. 🙁

Thus I was really excited to learn that Dr. Mache Seibel has studied this controversy extensively and has shared some good news regarding the use of Hormone Replacement Therapy:

  • It was the synthetic progestin (Provera), and not estrogen that caused many of the associated health concerns… Our bodies make progesterone, and progestins are a synthetic “cousin” that can be associated with greater risks. Taking bioidentical progesterone can alleviate those risks!
  • There was also a decade in age difference of women who got placebo vs. the HRT. The women who received HRT were older, and as we know our risks of disease go up with age, this could have been a confounding variable. When the age difference was taken into consideration, the report changed. The rates of breast cancers in women taking HRT were minimal, compared to the initial estimates. And women who took HRT lived longer!
  • Estrogen may actually *reduce* the risk of many cancers!

Dr. Seibel is a medical doctor who has found that women have an “Estrogen Window,” which is a time period where using estrogen will be beneficial, and the associated risks will be minimized.

The “Estrogen window” is a time period between 5-10 years, usually right after a woman begins menopause. This is the optimal time to take estrogen/progesterone (or estrogen only for women who have had a hysterectomy). Taking estrogen past or after the “Estrogen Window” may be associated with greater risks of breast cancer…

Here’s a guest blog post from Dr. Mache Seibel on the Estrogen Window and his new patient guide on the topic, where he addresses how to determine your individual estrogen window.

Why I Needed The Estrogen Window and Why You Do Too

By: Mache Seibel, MD

Early in my career, I was one of the first people to successfully perform in vitro fertilization (IVF) in the United States. It was a very exciting time, and I was able to help so many women achieve their dreams of having a baby after years of infertility.

But after 20 years of huge success, many of my patients were transitioning into menopause and wanted me to continue being their doctor.

Around that same time, a study called the Women’s Health Initiative (WHI) reported that women who took an estrogen-containing medication, PremPro, had an increased risk of developing breast cancer, heart disease, and some other worrisome conditions. Women felt angry and afraid and not surprisingly, hundreds of my patients stopped taking estrogen. Without estrogen, they felt miserable. My initial look at the original data caused me to question the negative findings, but it would take over a decade for new studies to prove how wrong the first WHI study was.

Seven months after that WHO report was published, a new BReast CAncer gene called BRCA was identified that increased the risk of breast and ovarian cancer. My wife, Sharon, had lost many of the women in her family at an early age due to ovarian cancer and had the test done. Unfortunately, it was positive, and at a relatively early age, Sharon had her fallopian tubes and ovaries removed. That sent her into early menopause. Her doctors were fearful of giving her estrogen because of the new WHI study and the fact Sharon had the BRCA gene. I had to know if estrogen was safe for her and my patients.

So I went about it the way I do all my research, fully intent on getting an accurate answer. It wasn’t easy. Have you ever taken something apart and putting it back together found there were a few pieces left over and no logical place to put them?

In the meantime, I started a new online My Menopause Magazine (in the Apple Newsstand and on Google Play). As an editor, I went to all the major meetings and interviewed virtually all the researchers who did the studies on menopause and asked them question after question until I could make all the pieces fit. After all, not only did I need to know for my patients; I had Sharon to advise.

Finally, I had a breakthrough. It clarified how estrogen prevents heart disease and could cause heart disease; how it could lower the risk of breast cancer and increase breast cancer risk; and on and on. The reason was what I call The Estrogen Window.

Estrogen isn’t good or bad. It’s both and neither. It all depends on when it is taken.

If a woman begins estrogen early in her estrogen window, it will lower her risk of breast cancer, heart disease, and type 2 diabetes, and maximize the treatment of symptoms. If begun after the window closes, symptom relief can be reduced, and it can increase the risk of heart disease and have no effect on osteoporosis. It also matters if a woman takes estrogen only or estrogen plus a progestogen, which is required for women who have not had a hysterectomy.

Because this information is essential for women (and many of their doctors) to know to clear up their fear and confusion, I wrote a very easy to read explanation of one of the most complex problems in women’s health.

When you read it, you will be empowered to talk with your healthcare provider to determine if estrogen is right for you: which one, when to start it and when to consider stopping it. You’ll discover the negative impact not taking estrogen had on women’s health, relationships and effectiveness in the workplace. You’ll understand the difference between the various routes of taking estrogen and some critically important facts about the risks and benefits of bioidentical and compounded hormones. And most importantly, you’ll be empowered to make the best choices for your health and be a messenger to help your friends and family. And that will be transformative.

Note from Dr. Izabella
I hope that you find this information helpful in your journey. I had the pleasure of reading a copy of Dr. Seibel’s book and found that it clarified a lot of my questions about hormone replacement therapy and how to advise my clients on the risks/benefits.  If you are going through menopause, taking hormone replacement therapy, or thinking about it, Dr. Seibel’s work will help you get some clarity and will help you determine what your unique estrogen widow may be.


  1. Questions and Answers About WHI Postmenopausal Hormone Therapy Trials, NHLBI, WHI. Nhlbinihgov. 2017. Available at: https://www.nhlbi.nih.gov/whi/whi_faq.htm. Accessed June 29, 2017.
  2. Breast cancer (female) – Causes – NHS Choices. Nhsuk. 2017. Available at: http://www.nhs.uk/Conditions/Cancer-of-the-breast-female/Pages/Causes.aspx. Accessed June 29, 2017.


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