Breast cancer (BC) is the most common cancer in women in the United States. There has been an increasing incidence and decreasing mortality rate of BC cases over the past several decades. Many risk factors are associated with BC, such as diet, aging, personal and family history, obesity, and some environmental factors. Recent studies have shown that healthy individuals and BC patients have different microbiota composition, indicating that microbiome is a new risk factor for BC. Gut and breast microbiota alterations are associated with BC prognosis. This review will evaluate altered microbiota populations in gut, breast tissue, and milk of BC patients, as well as mechanisms of interactions between microbiota modulation and BC. Probiotics and prebiotics are commercially available dietary supplements to alleviate side-effects of cancer therapies. They also shape the population of human gut microbiome. This review evaluates novel means of modulating microbiota by nutritional treatment with probiotics and prebiotics as emerging and promising strategies for prevention and treatment of BC. The mechanistic role of probiotic and prebiotics partially depend on alterations in estrogen metabolism, systematic immune regulation, and epigenetics regulation.

Consumption of dietary natural components such as genistein (GE) found in soy-rich sources is strongly associated with a lower risk of breast cancer. However, bioactive dietary component-based therapeutic strategies are largely understudied in breast cancer treatment. Our investigation sought to elucidate the potential mechanisms linking bioactive dietary GE to its breast cancer chemotherapeutic potential in a special subtype of aggressive breast cancer—triple-negative breast cancer (TNBC)—by utilizing two preclinical patient-derived xenograft (PDX) orthotopic mouse models: BCM-3204 and TM00091. Our study revealed that administration of GE resulted in a delay of tumor growth in both PDX models. With transcriptomics analyses in TNBC tumors isolated from BCM-3204 PDXs, we found that dietary soybean GE significantly influenced multiple tumor-regulated gene expressions. Further validation assessment of six candidate differentially expressed genes (DEGs)—Cd74, Lpl, Ifi44, Fzd9, Sat1 and Wwc1—demonstrated a similar trend at gene transcriptional and protein levels as observed in RNA-sequencing results. Mechanistically, GE treatment-induced Cd74 downregulation regulated the NF-κB/Bcl-xL/TAp63 signal pathway, which may contribute to soybean GE-mediated therapeutic effects on TNBC tumors. Additionally, our findings revealed that GE can modify expression levels of key epigenetic-associated genes such as DNA methyltransferases (Dnmt3b), ten-eleven translocation (Tet3) methylcytosine dioxygenases and histone deacetyltransferase (Hdac2), and their enzymatic activities as well as genomic DNA methylation and histone methylation (H3K9) levels. Collectively, our investigation shows high significance for potential development of a novel therapeutic approach by using bioactive soybean GE for TNBC patients who have few treatment options.

Breast cancer (BC) is among the most frequently diagnosed malignant cancers in women in the United States. Diet and nutrition supplementation are closely related to BC onset and progression, and inulin is commercially available as a health supplement to improve gut health. However, little is known with respect to inulin intake for BC prevention. We investigated the effect of an inulin-supplemented diet on the prevention of estrogen receptor-negative mammary carcinoma in a transgenic mouse model. Plasma short-chain fatty acids were measured, the gut microbial composition was analyzed, and the expression of proteins related to cell cycle and epigenetics-related genes was measured. Inulin supplementation greatly inhibited tumor growth and significantly delayed tumor latency. The mice that consumed inulin had a distinct microbiome and higher diversity of gut microbial composition compared to the control. The concentration of propionic acid in plasma was significantly higher in the inulin-supplemented group. The protein expression of epigenetic-modulating histone deacetylase 2 (Hdac2), Hdac8, and DNA methyltransferase 3b decreased. The protein expression of factors related to tumor cell proliferation and survival, such as Akt, phospho-PI3K, and NF-kB, also decreased with inulin administration. Furthermore, sodium propionate showed BC prevention effect in vivo through epigenetic regulations. These studies suggest that modulating microbial composition through inulin consumption may be a promising strategy for BC prevention.

Background: Breast cancer (BC) is the second most common cancer among women in the United States. It has been estimated that one in eight women will be diagnosed with breast cancer in her lifetime. Various BC risk factors, such as age, physical inactivity, and smoking, play a substantial role in BC occurrence and development. Early life dietary intervention with plant-based bioactive compounds has been studied for its potential role in BC prevention. Sulforaphane (SFN), an isothiocyanate, is an antioxidant and anti-inflammatory agent extracted from broccoli sprouts (BSp) and other plants. Dietary supplementation of SFN suppresses tumor growth by inducing protective epigenetic changes and inhibiting cancer cell proliferation. Inulin, as a dietary fiber, has been studied for alleviating GI discomfort and weight loss by promoting the growth of beneficial bacteria in the gut. Objective: Early-life combinatorial treatment with both phytochemical SFN and potential prebiotic agent inulin at lower and safer dosages may confer more efficacious and beneficial effects in BC prevention. Methods: Transgenic mice representing estrogen receptor-negative BC were fed 26% (w/w) BSp and 2% (w/v) inulin supplemented in food and water, respectively. Results: The combinatorial treatment inhibited tumor growth, increased tumor onset latency, and synergistically reduced tumor weight. Gut microbial composition was analyzed between groups, where Ruminococcus, Muribaculaceae, and Faecalibaculum significantly increased, while Blautia, Turicibacter, and Clostridium sensu stricto 1 significantly decreased in the combinatorial group compared with the control group. Furthermore, combinatorial treatment induced a protective epigenetic effect by inhibiting histone deacetylases (HDACs) and DNA methyltransferases (DNMTs). Intermediates in the AKT/PI3K/MTOR pathway were significantly suppressed by the combinatorial treatment, including PI3K p85, p-AKT, p-PI3K p55, MTOR, and NF-κB. Cell cycle arrest and programmed cell death were induced by the combinatorial treatment via elevating the expression of cleaved-caspase 3 and 7 and inhibiting the expressions of CDK2 and CDK4, respectively. Orally administering F. rodentium attenuated tumor growth and induced apoptosis in a syngeneic triple-negative breast cancer (TNBC) mouse model. Conclusions: Overall, the findings suggest that early-life dietary combinatorial treatment contributed to BC prevention and may be a potential epigenetic therapy that serves as an adjunct to other traditional neoadjuvant therapies.