Oral mucositis (OM) is a common and impactful toxicity of standard cancer therapy, affecting up to 80% of patients. Its aetiology centres on the initial destruction of epithelial cells and the increase in inflammatory signals. These changes in the oral mucosa create a hostile environment for resident microbes, with oral infections co-occurring with OM, especially at sites of ulceration. Increasing evidence suggests that oral microbiome changes occur beyond opportunistic infection, with a growing appreciation for the potential role of the microbiome in OM development and severity. This review collects the latest articles indexed in the PubMed electronic database which analyse the bacterial shift through 16S rRNA gene sequencing methodology in cancer patients under treatment with oral mucositis. The aims are to assess whether changes in the oral and gut microbiome causally contribute to oral mucositis or if they are simply a consequence of the mucosal injury. Further, we explore the emerging role of a patient’s microbial fingerprint in OM development and prediction. The maintenance of resident bacteria via microbial target therapy is under constant improvement and should be considered in the OM treatment.

Purpose of review: A growing number of studies demonstrate the oral bacterial shift in cancer patients and the enrichment of oral bacteria in distant tumours. During the oncological treatment, opportunistic oral bacteria correlate with oral toxicities. This review focused on the most recent studies to identify which genera are the most mentioned and deserved further investigation. Recent findings: This review evaluated bacterial changes in patients with head and neck, colorectal, lung and breast cancer. Greater composition of disease-related genera (e.g., Fusobacterium, Porphyromonas, Lactobacillus, Streptococcus, and Parvimonas) are present in the oral cavity of these groups of patients. The tumour specimen characterisation of head and neck, pancreatic and colorectal cancer also describes the presence of oral taxa. No evidence indicates that commensal oral bacteria have protective roles in distant tumours. Regardless, oral care is critical to prevent the growth of oral pathogens and reduce infection foci. Summary: Recent evidence suggests that oral microbiota is a potential biomarker for oncological clinical outcomes and oral toxicities. Currently, the literature presents a remarkable methodological variety - from the sample collection site to the preference of the data analysis tools. For the oral microbiome to achieve the stage of being used as a clinical tool in the oncological context, more studies are necessary.

Autops Case Rep, vol.10, n2, e2020160, 2020

Radiotherapy-related caries (RRC) is an aggressive and debilitating oral toxicity that affects half of the patients who undergo radiotherapy for head and neck cancer. However, the etiology of RRC is not fully established, and there are no clinically validated methods for preventing it. To gain a better understanding of the risk factors and the microbiome’s role in causing RRC, we compared clinicopathological characteristics, oncological treatment regimens, oral health condition, and the oral microbiota at three different oral sites of radiotherapy-treated patients with (RRC+) and without radiotherapy-related caries (RRC−). We observed no significant differences between these groups in the clinicopathological characteristics and treatment regimens. However, RRC+ patients were older and had poorer oral health conditions at the start of the radiotherapy treatment, with a lower number of teeth and a higher proportion of rehabilitated teeth. RRC+ patients had lower microbiota diversity and the dental biofilm of RRC+ patients displayed striking alterations in microbiome composition compared to RRC− patients, including enrichment of acidogenic species and altered metabolic potential, with a higher abundance of genes linked to energy-related pathways associated with the synthesis of amino acids and sugars. We also compared the microbiota of RRC+ tissue with conventional caries tissue, revealing lower bacterial diversity and enrichment of Lactobacillaceae members in RRC+. The insights into the irradiated oral microbiota enhance the understanding of RRC etiology and highlight the potential for microbial-targeted therapies in its prevention and treatment. IMPORTANCE: This study focuses on a dedicated collection of diverse oral sites to comprehensively investigate microbial differences between patients who develop RRC and those who do not. RRC is a severe oral disease that profoundly impacts on the oral health and overall quality of life of cancer survivors. Leveraging shotgun metagenomics, we characterize the unique microbial variations in in vivo irradiated dental biofilms, unveiling novel insights into the microbial ecology of radiotherapy-treated patients. Furthermore, this research integrates extensive data on oral health and oncological profiles, providing a comprehensive understanding of the intricate relationship between oral microbial communities and the outcomes of radiotherapy-induced toxicity.