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Breast Cancer and Hormone Therapy

Updated: Jan 20

I did then what I knew how to do. Now that I know better, I do better."

― Maya Angelou

Chances are you know someone close to you who has had breast cancer. I know I do. 25 years ago, when my mom started her menopausal symptoms, she was given the usual combination of horse derived Estrogen and synthetic progesterone. She asked her doctor and me how safe hormone therapy was and how long she would need to continue. The doctor told her that her symptoms were severe, plus with a family history of heart disease, she would benefit from hormone therapy. In addition to that, there was no evidence to believe that hormones cause breast cancer. I had a detailed conversation with the drug rep who presented studies showing the benefits of hormones in women. My mom continued taking her pills diligently.

When she found a lump in her left breast and a biopsy confirmed that it was cancerous, we were devastated. Her cancer had spread to her lymph nodes. She went through a double mastectomy and chemotherapy. It was a very difficult time for her but also for me. (See my blog

The day I received a phone call about her diagnosis, was by far one of the worst days of my life. But then, it was also the beginning of my search for answers beyond what I was told by research. That is when I started researching hormone therapy and its consequences with a new magnifying glass. I began to learn about alternatives such as Bio-Identical hormone replacement therapy (BHRT). I was convinced that the hormones that my mom took played a role in her developing breast cancer but couldn’t really prove it. It wasn’t until the Women’s Health Initiative (WHI) study* results came out that we learned more about the effect of synthetic progestins on breast cancer.

Before the WHI study, there had been considerable evidence that estrogen with or without a progestin (synthetic Progesterone) might prevent disease in postmenopausal women. The WHI study was launched in the 1990s. It included 27,347 women between 50-79 years of age. These women were followed during active treatment (5.6 years in the estrogen-plus-progestin trial, 7.2 years in the estrogen-alone trial). In addition, they were followed for an extended period with no treatment, for a total follow-up of 13 years.

The results surprised the researchers as they had to stop the estrogen-plus-progestin arm of the trial because of an increased risk of breast cancer, heart disease, stroke, blood clots, and overall harm. The second arm of the study, the estrogen-alone arm which included women with no uterus, was later stopped early because of increased risk of stroke and no overall benefit. See the table below*; data taken from

During the estrogen-plus-progestin trial, breast cancer risk progressively increased to 24% overall. For every 10,000 women taking estrogen-plus-progestin for one year, there were 9 extra cases of breast cancer. These cancers were at a more advanced stage than in the placebo group. During the post-intervention follow-up period, the risk remained elevated. In the estrogen-alone trial, we observed a reduced risk of breast cancer among women assigned to estrogen compared to placebo. For every 10,000 women taking estrogen-alone for one year, there were 7 fewer cases of breast cancer. The effect was present but not statistically significant during the intervention phase, but it persisted after stopping, and the risk of breast cancer was significantly reduced (by 21%) over the 13-year follow-up.

Now, let us compare the above findings with the most recent published meta-analysis done by the Collaborative Group on Hormonal Factors in Breast Cancer. The study titled “Type and timing of menopausal hormone therapy and breast cancer risk” was published in The Lancet which is the world's leading independent general medical journal, on August 29th, 2019.**

The study was done on 108,647 postmenopausal women who had developed breast cancer at a mean age of 65 years. It showed that 55,575 (51%) had used menopausal hormone therapy. This implies that 49% of women who developed breast cancer had not used menopausal hormone therapy. Here is a summary of the findings from that study, plus other risk factors for developing breast cancer.

Overall % of women diagnosed with breast cancer in their 50’s 3%

The Collaborative Group on Hormonal Factors in Breast Cancer study (1992-2018)

Overall risk of developing breast cancer between 50-69 years of age (for women of average weight) 6.3%

The Collaborative Group on Hormonal Factors in Breast Cancer study (1992-2018)

Total number of Post-menopausal women who developed breast cancer at a mean age of 65 (included in the study) 108,647

The Collaborative Group on Hormonal Factors in Breast Cancer study (1992-2018)

Number of women who had used Menopause Hormone Therapy 55,575

This is 51% of the total number of women who had developed breast cancer

Risk of developing breast cancer for 5-year use of Estrogen only products 6.8%

This is a 0.5% increase compared to the baseline of 6.3%

Risk of developing breast cancer for 5-year use of Estrogen plus intermittent Progestagen 7.7%

This is a 1.4% increase compared to the baseline of 6.3%

Risk of developing breast cancer for 5-year use of Estrogen plus Progestagen daily 8.3%

This is a 2% increase compared to the baseline of 6.3%

Vaginal Estrogen or hormone use of less than 1 yearDid not increase the risk of breast cancer significantlyWomen who consume 3 alcoholic drinks per weekHave a 15% higher risk of breast cancer increase the risk of breast cancer by 2-3% factors: Lack of physical activity, No pregnancy, Not breastfeedingBased on the evidence, these factors may increase the risk of breast cancer

The latest study didn’t really show anything new. Again, the increased risk of breast cancer was more associated with progestagens (mainly synthetic progestins) rather than Estrogen therapy.

With Bio-Identical HRT, you are given natural Progesterone and not synthetic Progestagens. There is no evidence that natural or bio-identical Progesterone is 100% safe, but the molecular structure of it is different from synthetic progesterone (Progestins). Of course, if a cancerous tumor is Estrogen-receptor or progesterone-receptor-positive, these hormones may encourage the growth of that cancer. Over the past 20 years, I have seen thousands of women (and men) with hormonal imbalance. When using hormones, we have to take into consideration the right dose, for the appropriate duration, your past medical history, genetics, alcohol consumption, obesity and other risk factors such as the health of your bones and your heart. You should also have your hormone levels checked periodically, perform breast self-exam and go for mammograms regularly.

In all of these cases, it is crucial to discuss your medical history, conditions, and concerns with your healthcare provider.

Feel free to ask me or one of our knowledgeable pharmacists about the latest news on this subject. We understand that with so many conflicting studies over the past few decades, it can be overwhelming to decide what to do.

Sharzad Green, Pharm.D.

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