Tamoxifen for Breast Cancer and the Gut Microbiome’s Impact on Effectiveness

Tamoxifen is a drug that is designed to prevent and treat hormone receptor-positive breast cancer. Hormone receptor-positive breast cancer requires one or two hormones, either progesterone or estrogen, to grow.

While tamoxifen breast cancer treatment has been approved by the U.S. Food and Drug Administration (FDA) and has been available since 1998, more recent research has focused on how tamoxifen’s efficacy is impacted by the gut’s microbiome.

According to a study found in the journal mBio, which is published through the American Society for Microbiology, patients who have specific bacteria in their gut may see better results from this medication. A stool sample test can give better insight on if this is an appropriate drug for preventing and treating hormone receptor-positive breast cancer in some women.

What Does Tamoxifen Do To Your Gut?

When you take tamoxifen, it’s in the form of a pill. That pill will pass through your stomach and into your intestines where it’s broken down and absorbed into the blood.

To be effective in fighting breast cancer, the drug has to get to the liver. There, it’s converted into another form, and that form has a direct impact on hormone receptor-positive cancer.

If a sugar molecule attaches to the tamoxifen in the body, then the drug will be moved back into the intestine and flushed out of the body rather than moving into the blood stream. This problem is avoided in some people, as their microbiome has enough beta-glucuronidase in its gut bacteria to eat the sugar and release the drug into the blood stream where it can do its job.

According to Yasmine Alam, the lead study author and a Ph.D. candidate at the Department of Biological Chemistry, University of California Irvine, gut bacteria plays a significant role in the effectiveness of tamoxifen and has to be carefully considered.

“Specifically, we found that certain enzymes produced by gut bacteria, called β-glucuronidase, play a role in how tamoxifen is broken down. These enzymes help recycle tamoxifen back into the bloodstream, which can make the drug more effective. We discovered that a particular type of bacteria, Bacteroides fragilis, was strongly linked to the ability of these enzymes to affect tamoxifen levels in the blood in a positive way. This suggests that the gut microbiome plays an important role in how tamoxifen works in the body.”

Tamoxifen FAQs

Why Do Breast Cancer Patients Take Tamoxifen?

Tamoxifen is used to both prevent and treat hormonal breast cancer. By using tamoxifen, it’s possible to reduce the risk of breast cancer developing in the opposite breast and the chance of recurrence by up to 50%. It can also reduce the risk of an initial breast cancer diagnosis by 40%.

How Does Tamoxifen Work in the Body?

Within the body, Tamoxifen works by absorbing into the bloodstream and converting into a form that can occupy estrogen receptors. After it passes through the liver, it occupies estrogen receptors on breast cancer cells, which hinders estrogen’s ability to drive the growth and multiplication of cancer cells. It is effective only for hormone receptor-positive breast cancer and is not used for other forms.

What Does Tamoxifen Deplete?

Tamoxifen is designed to block estrogen activity in the body, which can help prevent the growth of cancerous tumors that require estrogen as a part of the growth process.

What Is the Best Five-Year Drug for Breast Cancer?

While no drug is the “best” because there are many factors to consider during treatment, Tamoxifen has been called the best five-year drug for breast cancer because of its usefulness for risk reduction in patients who adequately absorb it into the bloodstream.

It can be used to reduce risk by taking it once daily over a five-year period. After the initial five-year course of the drug, you will benefit from a reduced risk of breast cancer for another five years.

What Are the Negative Side Effects of Tamoxifen

Like other chemopreventative and hormone therapies, Tamoxifen does have some potential side effects. If you experience these side effects, you may want to talk to your medical provider about different treatment options. The most common side effects of this medication include:

  • Menopause-like symptoms, such as night sweats, vaginal dryness, and hot flashes.
  • Leg swelling
  • Skin rashes
  • Fatigue
  • Headaches
  • Nausea
  • Irregularity or loss of menstrual periods
  • Fluid retention
  • Weight gain

What Is the Biggest Risk With Tamoxifen?

The greatest risk of taking tamoxifen is the potential for rare side effects such as:

  • Deep vein thrombosis (DVT)
  • Strokes
  • Eye problems, such as cataracts
  • Endometrial (uterine) cancer

Where Can I Learn More About Tamoxifen Hormone Therapy?

For more in-depth discussion about breast cancer drug tamoxifen and how it is used in breast cancer treatment, you can explore these resources:

 

This article has been reviewed by Dr. Charles Weaver, Medical Advisor for Learn Look Locate and Medical Oncologist.

Learn Look Locate is proud to present expert insights from Dr. Charles Weaver, founder of Cancer Connect and a key contributor to our mission at Learn Look Locate. Dr. Weaver’s expertise is an integral part of our joint newsletter with Cancer Connect, which has been empowering breast cancer patients for over a decade. The newsletter is distributed monthly to over 30,000 women who have opted in and will support them from diagnosis through treatment and survivorship. You can sign up for the newsletter by scrolling to the top of the page and submitting your email.

Dr. Weaver’s involvement in Cancer First Calls and our Community Page reflects our commitment to providing comprehensive support and information to those affected by breast cancer. He continues to remain dedicated to the mission of educating and informing patients of their options. Read more about Dr. Weaver’s breast cancer insights here.

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