Aetiology of oral cancer

The aetiology of oral squamous cancer is complex. The main factors associated with this disease are tobacco and alcohol consumption. Each of these factors increases the likelihood of oral cancer and both show a strong dose-related increase in incidence. It would seem that heavy smoking and heavy drinking have a synergistic effect, leading to an exponential rise in relative risk (Fig. 17.1).

Tobacco is the main aetiological agent associated with oral cancer. The risk of oral cancer is related to the number of cigarettes per day and the length of time the

patient has smoked, giving rise to the concept of pack years, where a pack is equivalent to 20 cigarettes:

Number of cigarettes per day x Pack years = number of years smoked 20

This formulation allows a calculation of the relative risk of each patient. The relative risk returns to that of a non-smoker 10 years after the cessation of smoking. Topical tobacco, particularly, when mixed with areca nut, slaked lime, and betel and placed as a quid in the buccal sulcus, is a potent carcinogen. On the Indian subcontinent, where the practice of chewing tobacco is common, oral cancer makes up 40% of the total incidence of all carcinomas; it is also prevalent in Asian communities in the UK.

Alcohol per se does not appear to be a potent carcinogen but seems to potentiate the effects of tobacco. Someone who smokes 30 or more cigarettes per week has a relative risk of seven-fold that of a non-smoker. A person who drinks 40 or more units of alcohol per week has a relative risk of six-fold; if these factors are combined then the relative risk of oral cancer increases by a factor of 38.

Recent research suggests that genetic factors play a significant part in the promotion of oral cancer. Cancer is prevalent in some families and this can include oral cancer. There is a cohort of patients who develop oral cancer in the third or fourth decade. This group, mainly women, develop aggressive cancers with a poor prognosis.

Cellular biology investigations show that disturbances in the regulators of cell growth and cell death (apoptosis) lead to the development of oral cancer. This is a rapidly expanding field and it is likely that new prognostic indicators and cancer treatments will come from this research.

Other agents that may be implicated in oral cancer pathogenesis include malnutrition, poor dental hygiene, infective agents and sunlight in lip cancer.

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