Traditional risk factors:
- Tobacco: Oral cancer is 5-10 times more common in smokers than in non-smokers. A number of studies have shown that patients with oral cancer are far more likely to use tobacco products than the general population. The risk of oral cancer increases with the number of cigarettes consumed and the number of years that the habit has been pursued. After cessation of tobacco use, the risk of developing oral cancer declines. While cigarette smoking is the primary cause, other tobacco products have been implicated too. The heat generated from pipes has been suggested as causing some lip and palate cancers. Smokeless tobacco (chewing tobacco and snuff) is associated with cancers of the buccal mucosa and gingiva. Also implicated is betel nut, commonly used in some east asian countries.
- Alcohol: Alcohol abuse and development of oral cancer are related. Several studies have provided the basis for this linkage. Like cigarette smoking, the incidence of oral cancer declines with cessation of alcohol use. One study equated the effects of “hard liquor” with wine and beer by the “whiskey equivalents” More than 82% of patients who had developed cancer had used over 6 equivalents per day. These conclusions have been confirmed in later studies: heavy alcohol use is a major risk factor for development of oral cancer. Importantly, the effects of tobacco and alcohol in oral cancer development are synergistic.
- Sunlight: Exposure to actinic radiation (sunlight) is clearly associated with development of cancer of both squamous cell carcinoma and basal cell carcinoma of the lip, usually the lower lip.
More recently described culprits:
- Human Papillomavirus (HPV): HPV is a very common infection. There are low-risk and high-risk subtypes. Low-risk subtypes are responsible for papillomas and condylomas. Only the high risk subtypes play a role in the etiology of squamous cell carcinoma (SCC) of the oropharynx. Most cases (about 73%) of SCC of the oropharynx are related to HPV. In contrast, most cases of oral cancer are not HPV related (only about 2% are HPV related). The virus must integrate into the host genome in order to become carcinogenic. HPV is a very common infection and most people clear the virus without consequence.