Cecal microbiota and mammary gland microRNA signatures are related and modifiable by dietary flaxseed with implications for breast cancer risk.

Breast cancer is a leading cause of cancer mortality worldwide. There is a growing interest in using
dietary approaches, including flaxseed (FS) and its oil and lignan components, to mitigate breast cancer
risk. Importantly, there is recognition that pubertal processes and lifestyle, including diet, are important
for breast health throughout life. Mechanisms remain incompletely understood. Our research uncovers
a link between mammary gland miRNA expression and the gut microbiota in young female mice. We
found that this relationship is modifiable via a dietary intervention. Using data from The Cancer Genome
Atlas, we also show that the expression of miRNAs involved in these relationships is altered in breast
cancer in humans. These findings highlight a role for the gut microbiome as a modulator, and thus a
target, of interventions aiming at reducing breast cancer risk. They also provide foundational knowledge
to explore the effects of early life interventions and mechanisms programming breast health.