Probiotic bacteria may enhance the anti-cancer activities of breast cancer drug tamoxifen and other endocrine-targeted therapies, which could help reduce the risk of estrogen-positive (ER+) breast cancer, suggests a new study presented Monday at ENDO 2022, the Endocrine Society’s annual meeting in Atlanta, Ga.
While the majority of bacteria in the body are found in the intestinal tract, bacteria have been identified in other parts of the body, including the breast. Bacteria are part of the breast microbiome – the collection of all microbes such as bacteria, fungi, viruses and their genes. Studies have shown that breast tissue has a distinct microbiome, which changes in the presence of tumors or diet, according to lead researcher Katherine L. Cook, Ph.D., of Wake Forest University School of Medicine in Winston-Salem. , North Carolina.
Tamoxifen is a drug given to women to prevent a recurrence of ER+ breast cancer. Breast cancer is ER+ if it has estrogen receptors. This suggests that cancer cells, like normal breast cells, may receive signals from estrogen that tell the cells to grow. Tamoxifen is also given to reduce the risk of breast cancer in women at higher than average risk of the disease who have not been diagnosed. Tamoxifen is in a class of drugs called endocrine therapies. Other drugs of this type include aromatase inhibitors and Faslodex.
The new study had three parts. First, a preclinical mouse model was fed a healthy diet or a western diet and treated with tamoxifen for three months. They then assessed the bacteria in the breast tissue. They found high levels of Lactobacillus in animals given tamoxifen. Lactobacillus is a type of bacteria known as gram-positive. It is best known for its probiotic and anti-inflammatory activities.
The researchers then injected Lactobacillus in the mammary glands of mice that spontaneously develop breast tumors and found Lactobacillus the treated animals showed a decrease in the formation of mammary tumors. “This shows that the increase Lactobacillus in breast tissue decreases the risk of breast cancer,” Cook said. This suggests a potential role for Lactobacillus and other bacterial species to improve patient response to treatment and reduce the risk of breast cancer.
In the second part of the study, researchers looked at a large animal model in which the ovaries were removed to simulate menopause and subjects were treated with tamoxifen for 2.5 years. The researchers found that they too had high levels of Lactobacillus in breast tissue.
In the third part of the study, the researchers examined tissue from ER+ breast tumors of women who had been treated neoadjuvantly with one or two targeted endocrine therapies, aromatase inhibitors or Faslodex. After their breast cancer surgery, the tumors were analyzed. Women with high levels of Gram-positive bacteria in their tumors had lower levels of cancer cell growth.
“Taken together, our new research suggests that probiotic bacteria may enhance the anticancer activities of tamoxifen and other targeted endocrine therapies to reduce the risk of ER+ breast cancer,” Cook said.
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Journal of the Endocrine Society
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