Abstract
Dysbiosis in the oral environment may play a role in the etiopathogenesis of oral squamous cell carcinoma (OSCC). This review aims to summarize the current knowledge about the association of oral microbiota with OSCC and to describe possible etiopathogenetic mechanisms involved in processes of OSCC development and progression. Association studies included in this review were designed as case–control/case studies, analyzing the bacteriome, mycobiome, and virome from saliva, oral rinses, oral mucosal swabs, or oral mucosal tissue samples (deep and superficial) and comparing the results in healthy individuals to those with OSCC and/or with premalignant lesions. Changes in relative abundances of specific bacteria (e.g., Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus sp.) and fungi (especially Candida sp.) were associated with OSCC. Viruses can also play a role; while the results of studies investigating the role of human papillomavirus in OSCC development are controversial, Epstein–Barr virus was positively correlated with OSCC. The oral microbiota has been linked to tumorigenesis through a variety of mechanisms, including the stimulation of cell proliferation, tumor invasiveness, angiogenesis, inhibition of cell apoptosis, induction of chronic inflammation, or production of oncometabolites. We also advocate for the necessity of performing a complex analysis of the microbiome in further studies and of standardizing the sampling procedures by establishing guidelines to support future meta-analyses.
Highlights
Oral squamous cell carcinoma (OSCC) is the most common malignancy in the head and neck region
Hopper et al reported the existence of viable bacteria in deep parts of OSCC; some species were isolated only from either tumorous or nontumorous tissue samples [13]
This implies that bacteria, especially facultatively anaerobic and anaerobic bacteria, may survive in the tumor microenvironment
Summary
Oral squamous cell carcinoma (OSCC) is the most common malignancy in the head and neck region. In 2020, the number of new cases of OSCC worldwide was 377,713, and the number of deaths in the same year was 177,757 [1]. Patients with this diagnosis have a low survival rate and poor prognosis. Oral carcinogenesis is a multifactorial process involving the effect of the exposome and subsequent cytogenetic and epigenetic changes in keratinocytes. The effects of oral microbiota, i.e., internal exposome, are intensively studied in association with the initiation and progression of OSCC
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