What You May Not Know About Breast Cancer

1 in 8 women in the US will develop breast cancer in their lifetime

As the second most frequently diagnosed cancer* among women worldwide, breast cancer affects everyone. (*Second only to non-melanoma skin cancer.) If you haven’t had it yourself, it’s extremely likely that you know someone who has. The more women you know who have breast cancer, the more you begin to see that you may be at risk as well. 

As an Ob/Gyn I have seen many patients who had been diagnosed with breast cancer and came to me for help.  I always ask a patient with a new diagnosis, “Why or how did you get breast cancer?”  

It nearly always turns out that the underlying issue was never addressed. 

And let me tell you, when we identify the underlying issues that caused my patient’s breast cancer, it changes everything. She becomes empowered; she no longer feels like a victim. This is why I encourage all my patients to look at their risks, long before there’s ever a diagnosis of breast cancer.

The problem is that most women don’t know what they can do to reduce their risk. 

While there is certainly a genetic component to being diagnosed with breast cancer, and there are some well-understood lifestyle and environmental factors that can play a role, much of the “why” behind a breast cancer diagnosis is still somewhat elusive for any given woman. For a vast majority of breast cancer cases (estimated to be as high as 70%) precise causes remain unknown although there is a growing list of possible contributing factors. (1) 

I think about the patients I've had over the years who have come to me seeking help with their diagnosis of breast cancer. Because many of these women could no longer use estrogen hormone therapy to address menopausal or vaginal health symptoms, I frequently prescribed bioidentical hormones.

I would talk to them about potential underlying root causes that might have contributed to their breast cancer, or that might be a risk factor moving forward in their breast cancer treatment.

Many have been surprised that there are a number of risk factors over which we do have control (beyond the generally known lifestyle factors such as not smoking, etc.). It’s empowering to know there are things you can do! If you have already had breast cancer, it helps to realize you no longer have to wait for the second shoe to drop, or to hear the next diagnosis, because you can feel strong in taking action, and better protected by the discoveries that are being made regularly.

Today I want to talk about one potential risk factor associated with breast cancer that you may not know about: the health effects related to the trillions of microbes found throughout your body. These individual microorganisms include a diverse community consisting of viruses, bacteria, archaea, parasites and fungi.

It sounds yucky, I know, but thankfully they are mostly good guys. You need to take care of them because when they are out of balance or otherwise negatively affected, they may affect cancer development, its progression and aggressiveness. Studies suggest that microbes may contribute 16-18%, or even more, of worldwide malignancies across multiple cancer types. (2)  

There are distinct species of microbes, each populating different areas of the body (gut, mouth, urogenital, vagina, skin, and even breast tissue, etc.). Some microbes are protective, others increase the risk for infections, inflammation and even cancer. Particular microbial communities may even affect how a woman responds to different cancer treatments or drug therapies.

Some microbes affect how estrogen is metabolized and whether it is safely detoxed or recirculated in a woman’s body. These hormone-driven microbes have been associated with other breast cancer risk factors, as well as those found with aging (over 50 in particular) and obesity.

Emerging research highlights that there is, in fact, a mammary microbiome (breast tissue and nipple) that may be related to a woman’s risk of breast cancer.

In today’s article we’ll be discussing,

  • Your modifiable breast cancer risks
  • The world of the oncobiome (microbes and their influence on cancer)
  • The estrobolome (microbes and their influence on estrogen)
  • Breast cancer, obesity, insulin control and the microbiome
  • Defenses against breast cancer

Your modifiable breast cancer risks

One in eight women will develop breast cancer over their lifetime. One in 883 men will as well. (3) 

But how do you understand and modify your risks?

There are some risks you can’t really circumvent (including gender, age, high breast density, family and reproductive history, and genetic “susceptibility”). 

But there are many other modifiable risks you can mitigate by making intentional lifestyle changes. I’ll talk about some of these in this article; the good news is that focusing on reducing overall inflammation and strengthening your immune system can reduce your risks for all disease, including breast cancer. 

Let’s briefly look at what you can and can’t change in terms of your breast cancer related risk factors.

Genetics, family and reproductive history:

Your genetic makeup and overall family history relating to breast cancer can impact your risk of being diagnosed with breast cancer. This earlier article on  breast cancer prevention points out the various family associations that may increase your risk, such as having a mother, sister or daughter with the disease.

While genetic “susceptibility” does increase your risk, it is important to note that most women who get breast cancer do not have a family history of the disease. True, having a close relative with breast cancer does increase your risk (about 15% of women with breast cancer have a family member who has had it), (4)  but genetic expression can be modified. How you live your life can impact how genetic risks are turned on or off (this is called epigenetics).  

Think of epigenetics as different interpretations of a given set of genetic code, one ending in increased breast cancer risk, the other not. Through epigenetics, factors such as diet, exposure to heavy metals and other endocrine disruptors, smoking, heavy alcohol use, and stress (among others), all can affect a very technical genetic process called DNA methylation, leading to a different expression of inherited genes.

Also, there are some factors of a woman’s reproductive history that do influence her risk of breast cancer, but you can’t really modify your reproductive history. These factors include things such as your age when you first menstruate (earlier has higher risk) or having a later menopause (there is a higher risk due to a lengthier period of estrogen exposure over the course of a woman’s life).

There are other family and reproductive attributes that can impact risk as well. More extensive information on how to assess your risk based on genetics, family and reproductive history can be found on any number of cancer-related medical sites such as the  Susan G. Komen website. 

But it is empowering to understand the potential risk factors you can control; you just need to take action.

Environmental and lifestyle factors (modifiable risk factors):

Environmental and lifestyle factors you can either eliminate or change include: smoking heavy use of alcohol, poor diet, obesity (and insulin control), sedentary lifestyle, chronic stress, periodontal disease, radiation, oral contraceptive use, oral hormone replacement therapy (HRT), and exposure to hormone disruptors such as parabens and other chemicals in the environment, food and your personal care products. All of these factors can add to your overall risk…but remember, you can make decisions to completely remove them from your life.

Emerging factors influencing a woman’s risk for breast cancer:

Recent research adds new areas of research focus:  how the body’s microbes affect overall inflammation and immune system health, and in particular how that has been linked to breast cancer. You can modify your risks that are associated with an impaired microbiome.

Let’s start by reviewing what microbes and the microbiome are, and how they and cancer are interlinked.

The world of the oncobiome

Your body consists of trillions of microbes, with differing species and phenotypes living in different areas and organs (collectively called your  microbiome). As mentioned earlier much of your microbiome consists of microbes that are pro-health; they ensure nutrient absorption, support immune system health, and are needed for various metabolic processes that keep you healthy. They protect you from invading pathogens and modulate inflammatory responses. They are most often “good guys.”

Having genetic susceptibility and/or environmental impacts (due to a poor diet, drug/antibiotic use, food sensitivities, excess estrogen, obesity, stress, insulin resistance, etc.), however, can affect the positive pro-health nature of different populations of microbes. It can result in microbial dysbiosis (imbalance or dysfunction), leaky gut (when the intestinal barrier breaks down), systemic inflammation and aberrant immune responses. These types of lifestyle and environmental interrupts can also result in a reduction in microbial diversity, which is shown to result in a pro-inflammatory state, as well as increased estrogen metabolism and levels (all having been associated with increased cancer risk).

Research has found gut and breast microbiome associations with breast cancer

Research shows that both post-menopausal women and cancer patients have less diverse microbiomes (in what is called the enteromammary pathway, which is the gut to mammary gland pathway in the body). They also have greater numbers of particular species of microbes. (5) 

Breast tissue has also been found to have a unique microbiome with differences when comparing paired normal tissue with breast tumor tissues (within a given woman) as well as when comparing breast microbes found in women with and without breast cancer. (6, 7) 

The female breast, with its widespread vasculature, duct system and lymphatics is highly conducive to the growth of diverse microbial communities. Different types of microbes in breast tissue have been found to actually correlate with different breast cancer subtypes.

Nipple aspirate (fluid) in women who have had breast cancer (versus healthy controls) has found different populations of microbes than found in the normal controls. (8) 

Some studies have found less compelling differences, pointing to the difficulties, I think, associated with measuring microbial make-up across larger populations of women (think about how challenging it is to quantify patterns of microbial populations in certain tissue or the gut when each woman in the study brings with her so many variations in her genetic and lifestyle profile).

But this is the new world of the  oncobiome, where researchers study  how the microbiome and cancer affect each other. Scientists use next-generation sequencing techniques to measure the effects of differing microbial communities on resultant healthy or pathological states such as cancer; they can also use these cutting-edge techniques to identify microbe species diversity.

To date they have found, (9) 

  • Certain “harmful” microbes are associated with cancer tissue (some have been identified and correlated with specific cancers; others are suspected)
  • These “harmful” microbes induce immune system changes or chronic inflammation, resulting in cancer growth
  • Harmful microbes may be found in the gut and in localized tissue (so, in both the gut and in breast tissue in the case of breast cancer)
  • Certain “beneficial” microbes appear to stimulate the immune system, thereby suppressing cancer activity and providing a localized protective effect
  • Loss of “beneficial” microbes, or causing their dysfunction, results in loss of immune stimulation and causes potential cancer growth
  • Certain microbes may influence the effectiveness of different anticancer treatments and drugs
  • Some microbes - or a reduction in microbial diversity - may contribute to the development of hormone-driven (estrogen) malignancies such as breast cancer

This last point introduces us to the  estrobolome. This is the term used to refer to hormone-driven microbes, estrogen being of primary concern. 

The estrobolome

Breast cancer has been shown to be directly related to higher levels of circulating endogenous estrogens as well as changes in normal estrogen metabolism (especially among postmenopausal women). (10) 

Where is all of this estrogen coming from? 

The use of hormonal contraceptives, the hormone imbalances of pregnancy and menopause, and hormone replacement therapy (HRT) can all exert effects on circulating estrogen by increasing levels or length of estrogen exposure. (11) Obesity, as well as other underlying metabolic states (such as insulin resistance) has been shown to be a risk factor for increased estrogenic effects and for breast cancer. (12-14) Endocrine disrupting products in your food, personal care products and environment can mimic estrogen’s effects in your body.

Research has found associations between the estrobolome and breast cancer

An increasing number of studies are also implicating involvement of the microbiome in the metabolism and recirculation of estrogen.

Species of gut microbes (the estrobolome) capable of producing estrogen-metabolizing enzymes have been identified, with clinical studies showing associations between those microbes and the levels of estrogen metabolites found in the body. (15)  It may be that estrogen-like compounds in the body can also increase the proliferation of certain species of harmful microbes as well.

So why doesn’t the body simply detox all of this excess estrogen? 

While normal conjugated (chemically combined for transport and detox) estrogens are generally excreted in the bile (and then into feces), certain bacterial species of microbes found in the gut can deconjugate (strip apart) these tightly packed estrogens. 

This leads to estrogen being reabsorbed into the circulatory system rather than detoxed and eliminated. These recirculating estrogens can then exert their effects on tissues such as breast tissue, stimulating growth and proliferation of hormone-driven malignancies either directly or indirectly (by impacting the immune system). Thus the estrobolome can affect estrogen metabolism as well as both the excretion and the recirculation of estrogens.

Such troublesome microbes found in the estrobolome have been found to be shaped in many cases by external factors (remember, these are modifiable factors over which we have control!) such as poor diet, a sedentary lifestyle, heavy alcohol use, obesity, etc. (16, 17) 

In particular there have been studies that have found a typical “Western diet” to be associated with higher estrogen metabolism and levels. (18, 19) Foods found in the Western diet such as refined grains and processed meats have been associated with inflammation.

On the other hand, one study found that a Mediterranean Diet (high in vegetables and fruits, oils and having foods with higher proportion of unsaturated fats versus saturated fats) instead showed anti-inflammatory properties as well as some anti-estrogenic properties. The diet resulted in a 40% decrease in total urinary estrogen levels in postmenopausal women. Anti-inflammatory foods have been inversely associated with breast cancer. (20) 

Other factors have additionally been shown to impact estrogen metabolism, such as the lack of physical activity. One study found that physical activity participation resulted in reduced adiposity and reduced estrogen metabolism. (21) 

Having a poor diet, a sedentary lifestyle, obesity or insulin control issues increases one’s risks for having breast cancer. Many microbe species found enriched in obesity are similar to those observed in breast cancer samples when compared to normal breasts. Let’s talk a bit more about this.

Breast cancer, obesity, insulin control and the microbiome

There are many linkages between breast cancer, gut microbiome health, insulin control and obesity. Obesity has been found to be partially influenced by specific microbial communities in the gut, likely in part due to long-term dietary choices. An impaired gut microbiome affects processes such as gut barrier integrity (keeping leaky gut and systemic inflammation at bay), the production of hormones affecting satiety (and appetite/food intake) and insulin control, glucose/lipid metabolism, and changes in metabolic signaling; these can all contribute to obesity and inflammatory disease. (22)  

Another role of the gut microbiome is in regulating fat storage (referred to as energy harvest). Distinct microbial communities found in obese individuals may be more efficient at harvesting and extracting energy from a given diet than that of lean individuals. For example, gut microbiome impairment/dysbiosis has been associated with an increase in microbes that encode enzymes specific to carbohydrate metabolism, encouraging excessive fat accumulation. (23) Different species of microbes have been found to be more (or less) abundant in obese animals in lab studies. There is actually quite a bit of research relating to this topic of body fat, obesity and their impact on inflammation and a whole host of negative health conditions.

In women, where does all of this fat storage go? 

Well, most of us would say it goes to our bellies, and it does. But it also goes to our breasts. 

The fatty acid-rich environment of breast tissue is one major location for adipose tissue, where fat is stored in your body. The concern? Adipose tissue is not just a storage location but is an active organ with important metabolic and endocrine functions. Estrogen accumulates in the adipose tissue of the breast as well as other tissues and there are a number of positive associations between such estrogen accumulation and breast cancer; in particular, estrogen receptor (ER)-positive breast cancer.

Finally, newer research is pointing to the gut microbiome as a key player in the development of chronic low-grade inflammation, which can result in metabolic diseases such as insulin resistance, obesity, hyperglycemia development and even Type 2 Diabetes. (24) 

An impaired microbiome – overall risks

Here’s a graphic that encompasses many of the elements of an impaired microbiome relating to breast cancer risk. Don’t let the graphic overwhelm you. Focus on the causes up on the right…these are all modifiable. 

Defenses against breast cancer

So can women improve their gut or breast microbiome in order to prevent breast cancer?

Well, not by simply taking a single pill or probiotic (although pre- and probiotics can be helpful).

While studies have shown some associations, such as the consumption of kefir and fermented foods, with a lower risk of breast cancer; or that Lactobacillus may have a protective role, it is only one preventive step. And it certainly can’t be the only step. You may need to tackle many of the causes listed on the earlier graphic in order to support a healthier microbiome and optimize  your risk reduction for breast cancer and other inflammatory diseases.

So what are the specific health goals you need to address and what specifically should you do?

Based on the research you want a diet and lifestyle protocol that will

  • Be anti-inflammatory
  • Boost your immune system
  • Reduce your overall acidity
  • Provide ongoing and healthy detoxification
  • Be supportive of gut microbial diversity
  • Maintain your gut intestinal barrier to prevent infections and inflammation
  • Reduce estrogen metabolism and levels
  • Provide insulin control
  • Balance hormones
  • Help maintain a healthy BMI
      • Consist of a proven anti-cancer diet (high vegetable, high fiber, no sugar, low refined carbs, no processed “white” foods, no reactive foods such as gluten, and supportive of producing short chain fatty acids) and anti-cancer lifestyle (moderate exercise, no smoking, improved stress management, limited alcohol, reduce exposure to endocrine disruptors, etc.)
  • Provide antioxidants and other superfoods shown to have anti-cancer properties
  • The good news?

    My Keto-Green® Diet and Lifestyle Program addresses all of these goals.

    Dr Anna Cabeca's diet tips for better breast health

    It is anti-inflammatory and provides the  many health benefits of alkalinity which include reducing pro-inflammatory states such as insulin resistance, metabolic syndrome and obesity. (25, 26) 

    It provides all the best of the traditional ketogenic diet (the  health benefits of ketones including supporting a healthier weight, reduced body fat, and improved insulin control) but addresses some of the traditional limitations of that diet, including typical keto diets being highly acidic (which is pro-inflammatory) as well as being known to reduce gut microbiome diversity. (27) 

    My Keto-Green diet is based on ketogenic principles that result in producing short chain fatty acids (SCFA), which are healthiest for the microbiome. SCFAs support the integrity of the intestinal lining (protective against leaky gut) and promote the activity of Treg cells (Treg cells support immune tolerance of “good” microbes so your immune system doesn’t attack good guys or even you, which can trigger auto-immune conditions).

    Alternatively, the typical “Western” diet results in a reduction in short chain fatty acids, increasing metabolic processes that result in the expansion of bacteria and chronic inflammation.

    My Keto-Green diet also incorporates  intermittent fasting which further supports gut microbiome diversity, insulin control, reduced body fat (potentially reducing unhealthy estrogen levels) and improved circadian rhythm. (Did you know the body’s microbiome actually has its own circadian clock, and fasting helps optimize the microbiome’s metabolic functions and keeps them healthy?) (28) 

    Intermittent fasting provides a reduced risk of breast cancer. In a study examining the self-reported duration of overnight intermittent fasting and breast cancer incidence, a prolonged overnight fasting period of ≥12.5 hours correlated with  reduced breast cancer risk. Researchers concluded that intermittent fasting likely improves insulin sensitivity as well as having anti-inflammatory effects due to improved sleep (given your digestive system can relax and repair itself).

    Intermittent fasting also supports a cellular “cleaning” process called autophagy, getting rid of garbage cells that have a greater risk of becoming cancerous.

    Finally let’s talk about leaky gut.

    You could already be suffering from leaky gut. Because it is the result of many of the earlier-noted causes for having an impaired microbiome, it is pervasive in many populations.  One of the chief culprits can often be reactive foods such as dairy. (Unfortunately dairy is my kryptonite; eating even a tiny bit will leave me with drainage in my ears and digestive symptoms that will last for days). Eating Keto-Green removes most of these microbiome offenders, including refined carbs, sugar, unhealthy fats and gluten. Another culprit for leaky gut, by the way, is the overuse of artificial sweeteners (so remove those from your grocery list)! It is vital to keep your intestinal barrier intact or you will experience both chronic and localized inflammation (potentially in your breasts!)..

    My Keto-Green program is not just about diet (nor is leaky gut simply the consequence of eating a poor diet); it also incorporates many external lifestyle and environmental interventions. Improving stress management is another part of the program. Stress, and the accompanying elevated levels of cortisol, make the body acidic, impair the microbiome and can result in leaky gut. Sleep hygiene is another part of the program. I talk about these, and many other lifestyle interventions in my book,  The Hormone Fix as well as here on my blog.

    Keto-Green diet and the microbiome- infographic

    Bugs as drugs: Along with my Keto-Green diet and intermittent fasting I always suggest we use “bugs as drugs.” (Well, at least the healthy, friendly bugs!) As mentioned above, prebiotics and probiotics help keep your gut microbiome healthy and diversified. 

    By supporting your gut microbiome, certain probiotic bacterial strains may both prevent and treat breast cancer growth and metastasis. As one example, studies have found that Lactobacillus reuteri, a bacterium found in breast milk, has immunomodulatory effects and has been shown to inhibit the proliferation of breast cancer cells. (29) You can now purchase many probiotic drinks and foods containing many strains of bacteria that have been shown to support the gut in one way or another.

    Try fermented foods such as kefir, sauerkraut, pickles, and yogurt with active probiotic cultures. Take supplemental probiotics daily. I like Gut Thrive which contains 30 billion CFUs (colony-forming units) of four different beneficial strains of bacteria. I use this daily.

    And pay attention to your stool. You should be having one good bowel movement a day (good means it is brown and banana-shaped…not greasy, splattered, etc.). If you are constipated you are not detoxing well! That needs to be resolved. Check out this podcast, “Are you paying attention to what your poop is telling you?” 

    Other supplement suggestions for healthy breasts:

    • Mighty Maca®Plus Superfood green drink, because of its anti-inflammatory ingredients and its ability to alkalize and detoxify
    • Pura PPR cream which is a natural progesterone and pregnenolone combination cream.  Bioidentical progesterone has been shown to support breast health and improve symptoms of estrogen dominance. 
    • Zenful provides a targeted blend of vitamins and other ingredients that promote estrogen detoxification, provide antioxidants and cellular support, and often ease common PMS and menopause symptoms
    • Vitamin D, as found in Ray of Strength, supports strong bones, cardiovascular health, and healthy blood clotting 

    Microbiome health affects breast cancer treatment, too

    The gut microbiome appears to also influence how well anti-cancer drugs and therapies may work. It also metabolizes at least forty chemotherapy drugs and influences the response many women have to both immunotherapy and radiation treatments. (30, 31) 

    What I find exciting about this research is that it points to the premise that one’s microbiome may be used in the future to provide targeted, patient-centered breast cancer treatments...or perhaps even patient-specific prevention of breast cancer. 

    But even today we understand that a healthy microbiome provides you with enhanced protection and defenses against many inflammatory diseases including breast cancer.

    I hope you have found this informative. As always I welcome feedback and questions. That’s why I am the Girlfriend Doctor; you can ask me anything!


    (1)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121903/

    (2)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121903

    (3)  https://www.mdpi.com/2073-4409/9/5/1091

    (4)  https://www.cancer.org/cancer/breast-cancer/risk-and-prevention/breast-cancer-risk-factors-you-cannot-change.htm

    (5)  https://cancer.ucsf.edu/podcasts/2017/04/12/the-human-microbiome-and-breast-cancer.8272

    (6)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017946/

    (7)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6534876/

    (8)  https://pubmed.ncbi.nlm.nih.gov/31456069/

    (9)  http://www.albiogen.ru/upload/documents/ngs-oncobiome-application-note-1170-2017-003.pdf

    (10)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121903/

    (11) https://pubmed.ncbi.nlm.nih.gov/25555473/

    (12) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5088296/

    (13) https://pubmed.ncbi.nlm.nih.gov/17981890/

    (14) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121903/

    (15) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121903/

    (16) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3264051/

    (17) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017946/

    (18) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017946/

    (19) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6019153/

    (20) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6019153/

    (21) https://pubmed.ncbi.nlm.nih.gov/15286467/

    (22) https://pubmed.ncbi.nlm.nih.gov/31087391/

    (23) https://www.frontiersin.org/articles/10.3389/.

    (24) https://www.frontiersin.org/articles/10.3389/fendo.2019.00029/full

    (25) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3571898/

    (26) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2982796/

    (27) https://ucsdnews.ucsd.edu/feature/whats-in-your-gut

    (28) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560

    (29) https://www.mdpi.com/2073-4409/9/5/1091

    (30) https://www.mdpi.com/2073-4409/9/5/1091/htm#B196-cells-09-01091

    (31) https://pubmed.ncbi.nlm.nih.gov/31456069/



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    Dr. Anna Cabeca

    Dr. Anna Cabeca

    Certified OB/GYN, Anti-Aging and Integrative Medicine expert and founder of The Girlfriend Doctor. During Dr. Anna’s health journey, she turned to research to create products to help thousands of women through menopause, hormones, and sexual health. She is the author of best-selling The Hormone Fix, and Keto-Green 16 and MenuPause.

    Learn more about my scientific advisory board.