Today, despite vast advances in cancer diagnosis and treatment, breast cancer is still the leading cause of cancer-related deaths in women. Various factors such as race, age, family history, mutation in the BRCA1/2 gene, diet, inactivity, alcohol consumption, and estrogen levels have been identified as risk factors for breast cancer. In recent years, microbiota has also been recognized as a new risk factor in breast cancer. In fact, the change in the microbial balance that occurs due to many environmental and internal factors of the body can be effective in the spread of cancer by affecting the intracellular pathways and signals. Studies have shown that intestinal dysbiosis affects the spread of breast cancer by affecting the metabolism and production of estrogen, or mechanisms unrelated to estrogen, such as the production of microbial metabolites that affect the immune system and lead to chronic inflammation. In addition, it has been proven that the breast tissue also has its microbiota, the types of which are different in healthy people, patients, even in different stages of breast cancer, and its subgroups. In such a way that a large amount of Proteobacteria, Firmicutes, Lactobacillus, and Actinobacteria are observed in healthy breasts, while their ratio changes in cancerous tissues. Considering the relationship between microbiota and breast cancer, maintaining a healthy microbiota is a new and significant approach to reducing the risk of developing, spreading, and managing this cancer. In this regard, compounds such as probiotics that can affect the balance of intestinal microbiota are considered as an effective approach to prevent and treat breast cancer. Probiotics can stimulate the growth of beneficial bacteria and inhibit the growth of harmful bacteria by causing physicochemical changes and affecting the metabolism of the intestinal microbiota. Furthermore, the consumption of probiotics can prevent the proliferation of cancer cells and reduce the tumor size by balancing the immune system, reducing inflammation, and inducing apoptosis in the cancer cells. This study describes the importance of microbiota in breast cancer, the difference between microbiota in a healthy person and a sick person, and the role of probiotics in the treatment of breast cancer.
