Therapeutic and Adjuvant Effects of Probiotics in the Management of Oral Cancer: A Scoping Review of Preclinical and Clinical Evidence

Background/Objectives: Oral cancer remains a major global health challenge, with persistent limitations in treatment efficacy and significant therapy-related morbidity. Probiotics, owing to their immunomodulatory, anti-inflammatory, and microbiota-regulating properties, have emerged as potential therapeutic and adjuvant agents. This scoping review aimed to systematically map and critically appraise preclinical and clinical evidence regarding the therapeutic and supportive effects of probiotics in oral cancer. Methods: A comprehensive literature search was conducted across PubMed, Scopus, Web of Science, and Google Scholar without temporal restrictions, including studies published up to February 2026. Eligible studies comprised in vitro, in vivo, and clinical investigations evaluating the effects of live or non-viable probiotic interventions on oral cancer biology and related clinical outcomes. Results: Twenty-one studies were included: 13 in vitro, 3 in vivo, and 6 clinical studies. Preclinical evidence indicates that strains such as Lactiplantibacillus plantarum, Lactobacillus acidophilus, and Lacticaseibacillus paracasei exert selective antiproliferative effects (up to 85% inhibition) via apoptosis induction, modulation of PTEN/MAPK and NF-κB signaling, and reduction in pro-inflammatory mediators. In vivo models demonstrated tumor growth suppression and improved survival without significant toxicity. Clinically, probiotics reduced treatment-induced oral mucositis, improved salivary function, and enhanced microbiota stability and patient-reported outcomes. However, evidence on direct oncological endpoints remains limited. Conclusions: Probiotics demonstrate biologically plausible, strain-specific antitumor and supportive effects, with the strongest evidence supporting their role as adjunctive agents, particularly in managing treatment-related complications. Further well-designed in vivo and clinical studies are required to define optimal strains, dosing strategies, and integration with standard oncologic treatments.