Microorganisms and cancer of the oral cavity

Numerous microorganisms, such as bacteria, viruses and fungi, inhabit the oral cavity, and it has been pointed out that poor oral hygiene and chronic periodontitis increase the risk of oral squamous cell carcinoma (OSCC). However, the molecular mechanism whereby the risk of OSCC is increased under such conditions has not yet been clarified. Microbes in the oral cavity may elicit both innate and acquired immune responses, resulting in the establishment of uncontrolled inflammation such as chronic periodontitis. Further microbial attack and various host-derived factors may subsequently contribute to events such as genetic and epigenetic alterations, inhibition of apoptosis, increased cell growth, promotion of invasion and metastasis, and lymphangiogenesis, thus linking the chronic inflammation to OSCC. Here we review the various factors involved in promoting the development and progression of OSCC. The facts suggest the importance of early prevention and treatment of chronic periodontitis to maintain oral health and prevent serious diseases such as OSCC. Introduction Most malignant neoplasms of the oral cavity are squamous cell carcinomas (SCCs) [1], and many factors are involved in the development of oral squamous cell carcinoma (OSCC) [2]. Although the primary causes of OSCC are tobacco and alcohol [1], the malignancy can occur even in individuals who do not smoke and drink [3], suggesting that other factors may also play a role. It has been pointed out that poor oral hygiene [4-8] and chronic periodontitis [9-12] may increase the risk of oral cancer. Numerous microorganisms, inhabiting in the oral region, such as bacteria, viruses and fungi, may affect the development and progression of OSCC. In this article, we describe the association of oral microorganisms and host-derived factors with OSCC, and also emphasize the importance of early prevention and treatment of chronic periodontitis for maintaining oral health and preventing lethal diseases such as OSCC. Dental caries and cancer Dental caries, one of the two major common diseases of the oral cavity, is characterized by destruction of enamel, dentin and cementum by commensal gram-positive bacteria. As the condition progresses, pulpitis and apical periodontitis develop jointly as sequelae. In extreme cases, patients may develop osteomyelitis and periostitis of the jaw, maxillary sinusitis, or Ludwig’s angina, leading to potentially fatal sepsis or systemic inflammatory response syndrome (SIRS) (Figure 1). Therefore, early prevention and treatment of dental caries are clearly very important. Tezal et al. [13] have reported an inverse association between dental caries and head and neck squamous cell carcinoma (HNSCC) and showed an inverse association, although the reason for this remains unknown and further studies are needed. Association between periodontal diseases and cancer Periodontal disease is the other major common disease of the Correspondence to: Kaoru Kusama, DDS, PhD, Division of Pathology, Department of Diagnostic & Therapeutic Sciences, Meikai University School of Dentistry, 1-1 Keyakidai, Sakado, Saitama 350-0283, Japan, E-mail: [email protected]