The microorganisms flora that live symbiotically in human beings, known as “microbiota” or “microbiome” of the individual, are increasingly recognized as important players in health and disease. Microbial changes (dysbiosis) could contribute to the risk of developing health problems. Historically, the association of bacteria is seen with several human cancers. For example, gastric cancer is linked to Helicobacter pylori infections. Salmonella typhi is linked to some forms of gallbladder cancer. S. typhi is also a promising carrier of therapeutic agents for melanoma, colon, and bladder cancers. Various bacterial genes which produced estrogen-metabolizing enzymes have been identified. Accordingly, gut microbiota can modulate estrogen serum levels. On the other hand,proliferation of certain species of bacteria can be promoted by estrogen-like compounds. Hence, a crosstalk in both endogenous hormones and estrogen and microbiota -like compounds might synergize to provide protection from disease but also to increase the risk of developing hormone- related diseases.
Research in recent time suggests that the microbiota of women who has breast cancer varies from that of healthy women, indicating that certain bacteria may be associated with cancer development and assert different responses to therapy.
Breast cancer is the commonest cancer and the leading cause of cancer death among women globally. In India, 1 in 22 women will be diagnosed with breast cancer. Treatment approaches include surgery, chemotherapy, immunotherapy, radiation therapy. The breast microbiome may play a major role in the effectiveness of such therapies. For example, antibiotics can impact the effectiveness of chemotherapy, and some cancer drugs, such as cyclophosphamide, may depend on healthy gut flora. Microbes can have a systemic impact, in that they influence the induction, training and function of the immune response and can cause postsurgical infections. Bacterial dysbiosis may also be associated with breast cancer recurrence, particularly in women who are undergoing breast reconstruction or those who develop post-surgery infections. Some endotoxins such as tumor necrosis factor (TNF), have also been linked to metastatic spread. Therefore cancer susceptibility and recurrence may be influenced by breast microbiome, and commensal bacteria may influence response to therapy by modulating the tumor microenvironment.
Diverse types of bacteria can be found in the breast tissue, and this diversity is present irrespective of a history of lactation. In a study undertaken for 81 women in Canada and Ireland, Proteobacteria was the most abundant phylum in the healthy breast microbiome. The comparison of normal adjacent tissue from women with breast cancer and tissue from healthy women showed significantly higher relative abundances of Prevotella, Lactococcus, Streptococcus, Corynebacterium, and Micrococcus in healthy patients, and Bacillus, Staphylococcus, Enterobacteriaceae, Comamondaceae, and Bacteroidetes in breast cancer patients. These bacteria were capable to cause DNA damage in vitro. Moreover, decrease in some lactic acid bacteria, known for their beneficial health effects, including anti-carcinogenic properties was seen.
Women with breast cancer have a higher abundance of Enterobacteriaceae, Staphylococcus, and Bacillus when compared to women without breast cancer. E. coli, a member of the Enterobacteriaceae family, is common hospital-borne infectious agent that has multiple links to breast cancer. E. coli and Staph. epidermidis isolated from breast cancer patients induced DNA double-stranded breaks in HeLa cells. These changes due to bacteria can cause DNA damage in breast cancer patients. Metabolites of certain bacteria may also be capable of damaging DNA and leading to cancer, but this has not yet been shown in breast cancer.
A familiar probiotic which is found in yogurt and kimchi, Lactobacillus acidophilus, can reach the mammary gland and has a number of anti-cancer effects. Women who consume fermented milk products may see protective antioxidant effects. Lactobacillus and Lactococcus species are more common in healthy breast tissues than in cancerous tissues, and may have a role in breast cancer prevention. For example, Lactobacillus is known to upregulate the immune system and helps to decrease the abundance of C-reactive protein and IL-6, which are pro-inflammatory factors.
According to researchers, breastfeeding women who develop lactation mastitis from Staphylococcus may also benefit from Lactobacillus supplements. For women who undergo mastectomy or breast- conserving surgery, there may also be a role for probiotics in the therapy of postsurgical infections.
Whether supplementation with Lactobacillus directly prevents breast cancer has yet to be studied. Probiotic treatment is correlated with a significant decrease in the abundance of Escherichia coli and a significant increase in Bifidobacterium, a beneficial gut bacterium. The interplay between gut microbiomes and breast microbiomes have important consequences for breastfeeding—studies suggest that a breastfeeding mother’s gut microbiome has an important role in immune education in her infant. While much is known about breast milk microbiomes, separate sites within the breast (including breast skin tissue, breast skin swabs, and cheek swabs) have unique microbiome signatures. As mentioned previously, the microbes reside inside the breast tissue regardless of a history of infection or lactation.
RNA extracted from patient saliva samples can provide medically relevant information about the oral microbiome, oral carcinoma, breast cancer, and pancreatic cancer, and salivary RNA assays are therefore a promising tool for medical diagnosis. Under oral cancer, presence of specific salivary microbes (such as Prevotella melaninogenica, Capnocytophaga gingivalis and Streptococcus mitis) can be diagnostic markers. Whether or not certain microbes are coincidental or diagnostic for breast cancer is currently unknown.
The American Association for Cancer Research compared the oral and gut microbiomes in a correlative study of patients with and without breast cancer, and concluded that patients with periodontal disease were at an increased risk of postmenopausal breast cancer. As we continue to learn more about the breast microbiome, it’s important to consider the interactions between various organs and microenvironments within the human body. Characterizing the human microbiome throughout the body may play an important role in calculating cancer risk, diagnosis, and prognosis.