Oral microbiome and mucosal trauma as risk factors for oral cancer: beyond alcohol and tobacco. A literature review

Oral and oropharyngeal cancer represents the sixth more common type of cancer affecting the worldwide population. It has been estimated the number of 650,000 new cases per year globally and a greater prevalence has been registered among men. The main risk factors for oral cancer such as tobacco smoking and alcohol are uncontroversial and have been deeply investigated and evidenced in the scientific literature. Recently, viral infections related to Human Papilloma Virus (HPV), with the genotype 16 and 32, have shown a correlation mainly with oropharyngeal cancer (OPC) especially in the non-smoking and non-drinkers young adults. Its transmission is mainly related to sexually transmitted diseases (STDs) although its involvement in oral squamous cell carcinoma (OSCC) is still unclear. This review aims to explore the hypotheses of the OSCC etiology and other possible risk factors, such as chronic traumatisms, chronic periodontitis, and poor oral hygiene that affect directly the oral mucosa and might trigger the carcinogenesis process that should not be underestimated. Furthermore, in the last 10 years, the role of oral microbiome gained attention as a predicting biomarker, for a possible bacterial, viral, and fungal involvement in tumorigenesis.