Oral microbiome alterations after cancer treatment: a scoping review and analysis

Cancer therapies impact the oral cavity. Oral microbial changes occur following cancer therapy, but the nature, duration, and implications of these shifts are not well understood. Exposure to radiation, chemotherapy or cellular therapies has been associated with oral microbiome shifts toward dysbiosis and increased frequency of pathogenic species in the microbiome. Despite these findings, much remains unknown about cancer-therapy-related changes in the oral microbiome following specific therapies, and what the associated long-term oral health implications may be for cancer survivorship. We therefore conducted a scoping review of oral microbiome studies in patients undergoing cancer therapy to broadly synthesize the literature on the oral microbiome in the context of cancer therapy, categorize findings, and identify research gaps to inform future projects. This scoping review of the literature describes substantial changes in the oral microbiome during cancer treatment, specifically chemotherapy, radiation therapy, and stem cell transplantation. Across 62 studies, chemotherapy, radiation therapy, and stem cell transplantation were associated with substantial changes in oral microbial communities. Among studies that assessed alpha diversity, the richness of species that comprised the oral microbiome often increased, encompassing more microbial taxa, while the evenness of species decreased, suggesting that community change was dominated by a few species. Frequently observed changes included decreases in commensal taxa such as Streptococcus and Prevotella and increases in opportunistic organisms such as Candida albicans and Staphylococcus aureus. While mucositis was often studied, consistent microbial predictors of this outcome were not identified The present study lays the groundwork for future research on the unique oral microenvironment and health needs in cancer survivors. The alterations in microbiome composition associated with specific cancer treatment categories add to our limited understanding of the key role of cancer therapy modalities on the oral microbiome.