Micro-organisms as risk factors

Among young people (under the age of 45 years) with mouth cancer, up to 25 per cent appear not to have had any exposure to the major known risk factors such as tobacco, alcohol or betel. Other factors known to be involved in OSCC include solar irradiation in lip cancers. Immunodeficient patients may also develop oral potentially malignant and malignant neoplasms.

Besides these factors, infections such as poor oral hygiene, periodontal disease, chronic candidosis, and virus infections link statistically with OSCC. Human papillomavirus (HPV) infection is also increasingly implicated - particularly in oropharyngeal cancer (fig 1).

Bacteria

Many patients with OSCC have poor oral health, with carious teeth and periodontitis. The use of tobacco and alcohol are confounding factors difficult to control in epidemiological studies, but periodontal disease has been shown to increase the statistical risk for cancer. One study showed that practising no regular oral hygiene conferred a risk for oesophageal cancer when compared with those who undertook daily tooth brushing. Another large-scale casecontrol study involving 856 upper aerodigestive tract cancer cases and 2696 age- and sex-matched controls, showed that, compared with toothbrushing once per day, the adjusted odds ratio for brushing twice or more was 0.82 (95 per cent confidence interval: 0.68, 0.99) but for not brushing was 1.79 (0.79, 4.05), suggesting brushing might protect against cancer.