The breast has its own microbiome of bacteria, and new research has shown it can be influenced by diet, as can breast cancer tumours.
In 2018, scientists at Wake Forest School of Medicine, part of Wake Forest Baptist Health, showed that diet, just like the gut microbiome, can influence the breast microbiome.
Now, new research shows that diet, including fish oil supplements, can alter not only the breast microbiome, but also breast cancer tumours. The findings were published online in Cancer Research.
To untangle the relationship between microbiome, diet and cancer risk, researchers undertook a multi-pronged approach to study both animal models and breast cancer patients.
“Obesity, typically associated with a high-fat diet consumption, is a well-known risk factor in postmenopausal breast cancer,” said Katherine L. Cook, PhD, assistant professor in the surgery – hypertension and cancer biology departments at Wake Forest School of Medicine. “But there’s still a lot we don’t know about the obesity link to microbiomes and the impact on breast cancer and patient outcomes.”
In the first part of the study, mice susceptible to breast cancer were fed either a high-fat or a low-fat diet. Mice consuming the high-fat diet had more tumours, which were also larger and more aggressive than the tumours in the low-fat diet group.
Next, to study the microbiome, researchers performed faecal transplants. Mice consuming the low-fat diet received the high-fat diet microbiome transplant, and mice consuming the high-fat diet received the low-fat diet microbiome transplant. Unexpectedly, mice that consumed the low-fat diet and received a high-fat diet microbiome had just as many breast tumours as mice on the high-fat diet.
“Simply replacing the low-fat diet gut microbiome to the microbiome of high-fat diet consuming animals was enough to increase breast cancer risk in our models,” Cook said. “These results highlight the link between the microbiome and breast health.”
Researchers also conducted a double-blind placebo-controlled clinical trial with breast cancer patients, with patients either receiving placebo or fish oil supplements for two to four weeks before lumpectomy or mastectomy.
Results showed that fish oil supplementation significantly modified the breast microbiome in both non-cancerous and malignant breast tissue. For example, scientists found longer-term administration of fish oil supplements (four weeks) increased the proportional abundance of Lactobacillus in the breast tissue near the tumour. Lactobacillus is a genus of bacteria shown to decrease breast cancer tumour growth, suggesting potential anti-cancer properties of this intervention. Researchers also found decreased proportional abundance of Bacteroidales and Ruminococcus microbes in the breast tumours of patients taking the supplements, though the significance of this is not understood.
“This study provides additional evidence that diet plays a critical role in shaping the gut and breast microbiomes,” concluded Dr Cook. “Ultimately, our study highlights that potential dietary interventions might reduce breast cancer risk.”
Dr Cook’s team is also conducting further studies to see if probiotic supplements can affect microbiome populations in mammary glands and in breast tumours.
