Microbial Biomarkers of Breast Tumor and Mastitis: Deciphering the Delicate Balance between Potentially "Evil" and "Benign" Alliances in Mammary Microbiomes.

Introduction: Breast cancer and mastitis significantly impact women's health and their infants' wellbeing. The advent of metagenomic sequencing technology has opened new avenues to explore the relationships between mammary microbiomes and these diseases. Despite recent extensive studies, detailed understanding of the mammary microbiome-disease relationships remains incomplete. Methods and Results: Here, we apply the Specificity and Specificity Diversity framework (Ma 2024, BMC Biology) to identify unique/enriched species (US/ES) associated with mastitis, breast cancer, or their healthy controls. The US/ES lists contain potential biomarkers and offer fresh insights into the intricacies of mastitis etiology and the relationship between breast tissue microbiomes and breast cancer. Conclusions: (i) The dynamic balance between coexisting alliances of beneficial microbes and harmful microbes (including opportunistic pathogens) holds key to understanding mastitis etiology. (ii) Intra-tumor microbes may serve multiple roles - as oncogenic microbes, neutral bystanders, or tumor suppressors, and their dynamic balance can influence breast cancer onset and progression. (iii) Significant challenges remain in developing effective probiotics, prebiotics and infant formulas due to complex entanglements between beneficial and harmful microbes. This complexity suggests that broad-spectrum or one-size-fits-all probiotic approaches may prove inadequate, pointing instead to the need for personalized prebiotic/probiotic/infant-formula solutions to restore and maintain healthy mammary microbiomes.