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Breast cancer and your microbiome

Raise your hand if you've always wanted to be knee deep in bacteria, fungi, viruses and mold.

Turns out, we are.

It's called the microbiome, and there are hundreds of species that we now know of, spanning 3 million genes in our intestine alone. Two-thirds of the species in our gut are unique to us. Nothing is wasted in our microbiota: It provides roughly 10 percent of our calories every day, protects us, strengthens or weakens our immune system, and has an effect on how we respond to medications.

sliced vegetables in jars

What is the microbiome? Our microbiome is the genetic material found in the microbiota. The microbiota is made up of microorganisms that thrive everywhere in our body and on our skin. We've known that microbes are responsible for certain types of cancer, for example, cervical cancer. This knowledge led to a vaccine for HPV, which causes cervical cancer.

God bless the scientists who study these microorganisms, because these bugs are the new frontier in cancer research. And they're not just in our digestive system. Yes, the breast microbiome might yield clues to breast cancer prevention and treatment.

Why is the breast microbiome significant? It has yet to be studied, although we know that breastfeeding reduces the risk of breast cancer—all types—compared to those who never breastfeed. There is increased benefit when women breastfeed for at least a year. The reduced risk is small but statistically significant, about 2 percent over 5 months, and with limited evidence for reduced risk of ovarian cancer as well.

Never having given birth also increases the risk of breast cancer. It's always been assumed that the reduced risk of breast cancer from breastfeeding or giving birth, was due to less exposure to estrogen produced. The benefit from less cumulative exposure to hormones is still true.

But could there be protective bacteria produced by the breast from childbirth and nursing? An amazing fact is that new milk ducts are produced for each birth. Researchers don't even know how many milk ducts women have. And breast cancer always starts in the duct. Once cancerous cells escape the milk ductal system, cancer becomes invasive. (Lobules make breastmilk, while ducts carry the milk.)

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The breast is also currently the focus of an alternative to oral medications. A study now recruiting women will evaluate the effect of Tamoxifen (4-OHT) gel on breast cells in women with ER+ DCIS. As a topical gel doesn't enter the blood nearly as much as the Tamoxifen pill, the hope is that women with DCIS will have an alternative treatment with fewer side effects.

Aside from the microbiome of the breast, the gut microbiome is now seen as important for a better response to cancer therapies. In particular, immunotherapy, a cancer therapy that uses the immune system to beat cancer, seems to be more effective when there is a healthy microbiome. While immunotherapy is used for the treatment of triple-negative, metastatic breast cancer, the effect of the microbiome was seen in patients with melanoma, an aggressive form of skin cancer. A poor microbiome may also affect outcomes of a bone marrow transplant, and is being studied in pancreatic cancer patients.

It's well known that antibiotics can weaken the microbiome. This also means a weakened immune system. In a small study, antibiotics taken by cancer patients, even for a few days, meant dramatically worse survival rates, possibly because the response to immunotherapy was not as effective as it could have been. CT scans showed tumors grew faster in those patients. The effects were seen regardless of the type of cancer, or the antibiotics prescribed.

More studies are needed on the link between antibiotics and immunotherapy, and patients still need to take antibiotics when necessary. What about probiotics? There's conflicting data on whether probiotics may help the gut during cancer treatments. Patients with melanoma who took probiotics had fewer strains of the good bugs necessary for a good response to immunotherapy.

What constitutes a healthy microbiome? The strength of the microbiome is due to the number of microbes and diverse strains. The quality of your diet plays a major role, as does sleep, the environment, reducing exposure to toxins, and moving throughout the day. Fruits, vegetables, whole grains, beans, nuts, herbs, spices, and seeds, are known to strengthen the microbiome.

Fall apples

Increasing fiber is one of the best ways to improve the gut microbiome, and has an added benefit of lowering estrogen levels for breast cancer survivors. In fact, those who ate more fiber and whole grains responded better to specific immunotherapy treatment, possibly due to a healthier microbiome.

But a weakened microbiome has fewer types and number of microbes. High amounts of specific foods, including processed meats (rolled meats such as deli meats, hot dogs, and sausages), and foods with added sugars, can impact and weaken the microbiome.

Can we manipulate the microbiome to respond better to cancer therapy, whether it's in the breast, the skin, or the gut? The short answer is no, we can't tailor the exact number and strains of microbes to a specific cancer therapy yet.

The role of the microbiome in cancer therapy is an exciting area of research, especially for dietitians, who already have an important role in guiding cancer patients with better nutrition during cancer treatments. Now we can also have a major impact on designing individual strategies to strengthen the microbiome, resulting in better cancer outcomes.

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