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How Does Estrogen Cause Breast Cancer

Other Factors Which Influence Decision Making

Does Hormone Replacement Therapy Cause Breast Cancer? Estrogen Effects on Women!

The two most recent studies of HRT and breast cancer risk suggest that only thin patients experience an increased risk of breast cancer from either estrogen alone or the combination of estrogen and a progestin . When limiting analysis to thin women, only those taking HRT long term had a statistically significant increase in breast cancer risk. Obese women did not have an increased risk of breast cancer attributable to HRT. A family history of breast cancer, early age of menarche, late age of child bearing, a high-fat diet, obesity, increased breast density on mammograms, and certain benign breast lesions increase the underlying risk of developing a breast cancer. Finally, several studies suggest that the breast cancers that develop in women receiving HRT are less aggressive in type and are associated with a better prognosis .

Data Linking Estrogens With An Increased Breast Cancer Risk

Before examining the effects of progestins, it is first necessary to question whether estrogen alone increases the risk of breast cancer. Substantial data from animal and human studies provide support for a link between estrogen use and breast cancer risk. Administration of exogenous estrogen to rodents results in a high incidence of breast cancer . The use of antiestrogens or blockers of estrogen biosynthesis abrogates the development of breast tumors that occur spontaneously or are induced by carcinogens in rats . In women, early menarche, late menopause, and increased endogenous circulating estrogen levels increase the RR of developing breast cancer . Removal of both ovaries before age 35 lowers the risk of breast cancer by 75% over a 25-yr period of observation . Finally, antiestrogens such as tamoxifen and raloxifene reduce the incidence of newly diagnosed breast cancer as demonstrated by randomized, placebo-controlled trials in women .

Does Estrogen Cause Breast Cancer The Opinion Of Avrum Bluming And Carol Tavris

In an earlier article on this website, we pointed out the importance of estrogen and the perils of postmenopausal hormonal profile:

the dominant opinion among the researchers in cancer is that even slightly higher levels of estrogen in postmenopausal women cause an increased risk of breast cancerThus, it would seem that if we restore estrogen levels in postmenopausal women to the levels necessary to prevent osteopenia and osteoporosis, the risk of breast cancer would also increase.

It is therefore very interesting to learn the arguments of those who oppose the dominant opinion and argue against the causal link between estrogen levels and breast cancer.

Avrum Bluming, MD, and Carol Tavris, PhD in social psychology, recently appeared on different podcasts where they talked about their book Estrogen Matters.

One of the screenshots below shows the credentials of the authors. Before reading the credentials , note the following survival rule:

Survival Rule: In the modern world, credentials do not guarantee intelligence or competence.

  • Does estrogen cause breast cancer? The opinion of Avrum Bluming and Carol Tavris.

Instead of being mesmerized by credentials, to assess a presumed expert, you need to analyze thoroughly what he or she says and writes. Look for the presence of common sense, pattern recognition, capacity to think logically. Analyze how the person spends his or her career, how the person deals with the dominant dogmas and The Party Line.

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Does Hrt Increase The Risk Of Womb Cancer

The risk of womb cancer depends on the type of HRT.

Oestrogen-only HRT increases the risk of womb cancer. The longer this type of HRT is used, the bigger the risk. Thats why oestrogen-only HRT is usually only offered to those who have had their womb removed as they have no risk of womb cancer to begin with.

Combined HRT can reduce womb cancer risk. But combined treatment causes the biggest increase in breast cancer risk. So, its important to talk to your doctor about the balance of possible benefits and risks for you.

Similar to oestrogen-only HRT, tibolone also increases the risk of womb cancer.

What Is A Hormone Receptor

Progesterone and Breast Cancer

In breast cancer, hormone receptors are the proteins located in and around breast cells. These receptors signal cells both healthy and cancerous to grow. In the case of breast cancer, the hormone receptors tell the cancer cells to grow uncontrollably, and a tumor results.

Hormone receptors can interact with estrogen or progesterone. Estrogen receptors are the most common. This is why ER-positive is the most common form of breast cancer.

Some people are diagnosed with progesterone receptor-positive breast cancer. The key difference is whether cancerous cells are getting growth signals from estrogen or progesterone.

Testing for hormone receptors is important in treating breast cancer. In some cases, there are no hormone receptors present, so hormone therapy isnt a good treatment option. This is called hormone receptor-negative breast cancer.

According to, about 2 out of 3 people with breast cancer have some form of hormone receptors present. This makes them candidates for hormone therapy.

Read Also: What Doctor Checks Your Hormone Levels

Also Check: When Can Breast Cancer Occur

Risk Factors You Can Change

Weight. Being overweight after menopause increases your odds.

Drinking alcohol.Alcohol is linked to breast cancer. Compared with nondrinkers, women who drink one alcoholic drink a day have a very small increase in risk, and those who are moderate drinkers have about a 20% higher risk.

Hormone replacement therapy . Long-term use of estrogen and progesterone increases the risk of breast cancer. This risk seems to go away if you’ve stopped using them for 5 years or longer.

Being inactive. Your odds go up if you donât exercise.

Reproductive history. Having your first child after age 30 or never having a full-term pregnancy puts you at higher risk. So does not breastfeeding.

How Breast Cancer Forms And Multiplies

Cancer cells are triggered when a mutation in normal cells occur. This can happen due to well-known problematic lifestyle factors like living on junk food, chronic sunburn and cigarette smoking, but hormones can also play a big role. Once cancer cells are born they grow and divide to make more cancer cells, which form a tumor that may contain millions of cancer cells.

Cancers need a blood supply to provide them the oxygen, nutrients and hormones like estrogen, which help them grow and multiply. But as they get bigger they are often further away from the blood vessels so they need to set up their own supply. They do this by sending out signals that tell your body to grow new blood vessels like capillaries. This process is called angiogenesis. And it is ongoing, so once it occurs the cancer keeps getting bigger and then may start to spread to organs like your liver . Thats why scientists are working on cancer vaccines and drugs to try to halt the process of angiogenesis.

Breast cancer is often caused by cancer cells growing in the lobules, where milk is produced or the ducts, where the milk travels to the nipple. Breast cancer cells may then spread to surrounding breast tissue, then move to the lymph nodes under the arms and migrate to other parts of the body.

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Epigenetics And Cancer Risk

Many inborn risk factors for cancer are epigenetic. Epigenetics refers to physical modifications to DNA that do not alter the DNA material itself but affect how cells interpret the data contained within. The interpretation of genes in the conduct of day-to-day physiological functions is called gene expression. Epigenetic mutations are often passed from parent to child. Scientists now better understand the dynamic relationship between epigenetic mutations and cancer growth.

For example, tumor-suppressor genes perform important work in the body by as the name suggests fighting the growth of cancerous tumors. In patients whose TSGs have been suppressed or otherwise inhibited by epigenetic changes, the stage is set for cancer growth. Therefore, maintaining awareness of who, if anyone, has been affected by cancer in your family is crucial to determining your risk factor. This is why most primary care physicians and oncologists request a thorough review of cancer incidence among family members in their initial evaluation process.

Effects On Other Target Organs

38. Does Estrogen Cause Breast Cancer?

Tamoxifen and raloxifene have effects on other target sites that may affect the balance of clinical benefits and risks.


Tamoxifen has an agonist effect on bone and promotes a gain in bone density at least in post-menopausal women . Raloxifene also has estrogen agonistic activity in bone and increases bone mineral density . Raloxifene also decreases the risk of vertebral fractures in post-menopausal women with osteoporosis .

Cardiovascular system

Both tamoxifen and raloxifene have estrogen agonist effects on serum lipids with an increase in high density lipoprotein and a decrease in low density lipoprotein cholesterol and total cholesterol. Raloxifene decreased cardiovascular events by 40% in the MORE trial . Tamoxifen has been associated with a reduction in coronary artery disease in some but not all adjuvant or prevention trials . It is of interest that estrogen also increases high density lipoprotein cholesterol concentration, but does not decrease coronary artery disease events .


Tamoxifen has agonist effects on uterine endothelium and is associated with an increased risk of endometrial cancer in adjuvant trials . In contrast, raloxifene appears to have neutral actions on uterine endothelium and is not associated with an increased risk of endometrial cancer.

Central nervous system

Breast cancer prevention

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The True Risk Factors For Breast Cancer

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 women who don’t smoke.

Absolute risk is more absoluteyou 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.

Be Smart With Smartphones

Please, do NOT keep your cellphone in your bra. Cellphones may cause negative changes to tissues of our body. While there arent yet any studies on cell phones and breast disease, cancer expert, Robert Nagourney of the Nagourney Cancer Institute, shared a case of a young woman who regularly carried her cell phone in her bra and later developed multiple breast tumors in that exact spot. Of course, thats one person whose story was actually recorded, but its better to be safe than sorry.

Read Also: How To Tell If Your Hormones Are Off Balance

Also Check: Which Type Of Breast Cancer Has The Poorest Prognosis

Attributable Risk Of Breast Cancer From Hrt With Estrogens Plus A Progestin

Epidemiological data examining the risk of breast cancer from HRT report relative risk statistics to determine statistical significance . This methodology provides substantial statistical power to detect the effects of these agents that might be quite small in magnitude. As discussed extensively in a prior publication , the lay press, patients, and many physicians confuse the term relative risk with attributable risk. An understanding of the precise definitions of these terms, as detailed below, is important to judge the actual magnitude of risks involved.

Taking Estrogen With A Progestin Vs Estrogen Alone

Does estrogen cause breast cancer? The opinion of Avrum ...

Treating menopausal symptoms with estrogen and progestin together is known as estrogen-progestin therapy or combined hormone therapy. Although estrogen alone improves the symptoms of menopause, it increases the risk of cancer of the uterus . Adding a progestin to the estrogen lowers the risk of endometrial cancer back to normal. Because of this, EPT is given to women who still have a uterus . EPT can be given 2 ways:

  • Continuous EPT means the same dose of estrogen and progestin is taken each day. Women often prefer continuous EPT because it rarely leads to menstrual-like bleeding.
  • Sequential EPT means different amounts of each hormone are taken on specific days. There are different ways to do this. For example, estrogen can be taken by itself for 14 days, then estrogen plus progestin for 11 days, then neither hormone for 3 to 5 days. Other schedules involve taking progestin only every few months. This lowers the amount of progestin that you are exposed to. Monthly regimens are also thought to result in hormone levels that are more like the natural menstrual cycle. Cyclical EPT can produce bleeding like a menstrual period, but it can occur less often than monthly.

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Hormones And Breast Cancer Development

Cancer is generally believed to arise when dividing cells undergo mutations and these genetically damaged cells become susceptible to unrestrained division. Thus, female hormones and other hormones that affect growth of the mammary gland are potential risk factors for breast cancer. In contrast, factors that induce differentiation in the mammary gland, such as pregnancy and lactation, are likely to reduce the risk of breast cancer. The baseline risk is influenced, however, by higher mammary gland mass and several observations provide indirect evidence of the association between mammary gland mass and breast cancer risk : first pregnancy induces terminal differentiation of the breast epithelium and reduces breast cancer risk dense mammographic patterns reflecting the dominance of epithelial tissue over fatty tissue are associated with higher risk of breast cancer adult height and the attendant higher mammary gland mass is a significant risk factor women have more mammary gland mass than men and they experience a 100-fold higher breast cancer risk Caucasian women have more mammary gland mass than oriental women, who have a lower breast cancer risk the left breast is slightly larger on average than the right breast, and more likely to sustain breast cancer.

What Is Unique About The Young Mammary Gland That Makes It So Susceptible To Cancer Induction And Protection

The fact that two crucial reproductive events, menarche and young age at parity, have the greatest effect on lifetime breast cancer risk suggests that the young mammary gland represents a crucial window in tumorigenic susceptibility. Why this is the case is less clear. Based on the epidemiological evidence for this, a few hypotheses have been generated, but again few have been tested experimentally, and this work is largely restricted to rodent models.

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Tips To Help Prevent Estrogen Dominance A Risk For Breast Cancer In Women And Men

Low estrogen levels in women can cause weight gain, mood swings and headaches. It also raises the risk for cardiovascular disease, osteoporosis and dementia. And in men it may raise body fat, lower sex drive and contribute to erectile dysfunction.

Seems awful. But there is one bright spot lower levels of estrogen also lower your risk for breast cancer as well as other estrogenic cancers such as ovarian, uterine, thyroid and prostate. A pooled analysis involving nine studies suggested that having high levels of the estrogen estradiol doubles your risk for breast cancer, according to the Susan G. Komen Foundation.

There are different types of estrogen, says Dr. Andrea Klemes, endocrinologist and chief medical officer, MDVIP. Low levels of one type can lead to a host of health issues, while high levels of another type raise the risk for cancer.Estrogen is a group of female hormones comprising estrone, estradiol, estriol:

Genetics are involved in breast cancer but not as much as you might think. Less than 15 percent of breast cancer cases have familial ties, according to Hormones play a role in at least some types of breast cancer.

However, estrogen also plays a critical role in the development of breast cancer, according to a study published in Cancer Letters. Researchers found that cells involved in estrogen-receptor positive breast cancer cells one of the most common forms of breast cancer â need estrogen grow.

Breast Cancer Risk In Relation To Childbearing And Breastfeeding

Which Cancer is CAUSED by Estrogen? Uterine or Breast? – 102

Although childbearing protects against later development of breast cancer, it has been difficult to isolate the impact, if any, of breastfeeding because it is closely related to other aspects of childbearing. For example, women breastfeed only after they have had a livebirth, and the earlier they commence childbearing, the more children they tend to have and the longer their lifetime duration of breastfeeding. Also, patterns of childbearing and duration of breastfeeding vary and few of > 40 studies to date had sufficient power to detect small or moderate effects.

The Collaborative Group on Hormonal Factors in Breast Cancer published findings from a collaborative reanalysis of data from 47 epidemiological studies conducted in 30 countries which examined the role of both childbearing and breastfeeding on breast cancer risk. This summary of the current evidence on the relative contributions of childbearing and breastfeeding on breast cancer risk is based on the collaborative report .

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The Root Of Misinformation On Estrogen And Breast Cancer Risk

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 Premarinconjugated 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.

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.


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