The Influence of Vaginal, Intestinal, and Tumor Tissue Microbiota on Selected Malignant Tumors in Women

Gynecological malignancies and breast cancer impose substantial health and economic burdens. This review examines how local and systemic microbiota may affect epithelial integrity, inflammation, estrogen metabolism, and immunity. The vaginal ecosystem is the most extensively studied female microbial niche. Cervical cancer serves as the most illustrative clinical example: loss of stable Lactobacillus crispatus dominance and increased prevalence of anaerobic bacteria (anaerobic dysbiosis) are associated with persistent HPV infection, which directly elevates the risk of cervical precancerous lesions. The estrobolome is particularly relevant in endometrial cancer, where intestinal bacterial beta-glucuronidase activity may increase estrogen reabsorption, particularly in obesity and metabolic disease. In ovarian cancer, microbiota is being studied as a possible risk modifier in BRCA1 carriers, but the evidence remains exploratory. In breast cancer, intratumoral bacteria may shape the immune microenvironment, particularly in triple-negative disease. The primary limitation of current research is methodological heterogeneity. Low-biomass samples, such as those from the ovary or endometrium, are highly susceptible to technical contamination. Most studies are cross-sectional and cannot establish causality. Current evidence supports microbiota as a modifier, not a standalone marker or a substitute for standard diagnosis and treatment. Its most plausible near-term role is in multiparameter risk or response models, pending standardized prospective validation.