Does Lactobacillus Exert a Protective Effect on the Development of Cervical and Endometrial Cancer in Women?

Cervical cancer is a significant health problem with increasing occurrence and mortality. This infection-associated tumour is caused by the human papillomavirus (HPV). HPV infection is cleared by the immune system within 6-18 months in most patients; however, persistent high-risk HPV (hrHPV) infections can lead to the development of cervical cancer. Virus persistence is promoted by immunodeficiency, Chlamydia trachomatis infection, smoking, and age, as well as the imbalance of cervicovaginal microbiota and inflammation. The abundance of bacteria in the vagina favours the maintenance of a dynamic balance; their coexistence influences health or disease states. The eubiotic vaginal microbiota of reproductive-aged women is composed mostly of various Lactobacillus species (spp.), which exert protective effects via the production of lactic acid, bacteriocins, polysaccharides, peptidoglycans, and hydrogen peroxide (H2O2), lowering pH, raising the viscosity of cervicovaginal mucus, and hampering both the adhesion of cells to epithelial tissue and the entry of HPV. The depletion of beneficial microorganisms could increase the risk of sexually transmitted infections. Emerging therapies involve mucosal, intranasal vaccines, which trigger systemic and mucosal immune responses, thus protecting against HPV-induced tumours. The use of probiotics has also been suggested to affect various biological processes associated with tumourigenesis (inflammation, oxidative stress, apoptosis, proliferation, and metastasis).