Volume 9, Number 2, 1999
Oral Cancer Revisited: Rates and Risk Factors
Oral cancer is the sixth most common cancer worldwide,1 and may affect the tongue, cheeks, peridontium or any other part of the oral pharynx. It is usually seen more frequently in men than women, and depending on its location within the oral cavity, men may be affected two to six times as frequently as women. Oral cancer ranks as the fourth most frequent cancer among men and eighth for women, with its incidence varying broadly from one geographical region to another (see table of estimated rates). In developing countries, oral cancer poses a great problem; it is ranked the third most common form of cancer in these regions. The site of attack within the oral cavity can also vary between geographical areas. For example, while pharyngeal cancer is seen most frequently among men in many parts of the world,2,3 cancers of the tongue and mouth are preponderant in India.4,5 As demands for dental care increase in older age groups, dental care providers will likely see more patients at higher risk for oral cancer.
The incidence of oral cancer is
associated with increasing age. Rates rise dramatically after the age of 40, and reach a
plateau around the age of 60.2 Therefore, even if age-specific incidence rates
remain stable, increased aging in the populations of many countries means there will be
more older adults at high risk for oral cancers.
Racial differences in disease occurrence have also been reported. Studies currently indicate that black Americans experience significantly more oral and pharyngeal cancers than white Americans.3,6 Relative stability in the incidence of oral cancer among white males has been seen in the United States from 1975 to 1991. However, a disturbing finding indicates that although young white males between the ages of 15 and 34 years have low incidence rates (1.1 per 100,000 persons) compared to the average, this age group showed a 267% increase in the incidence of mouth and pharyngeal cancers, from 0.3 per 100,000 over the study period.7
Over the last four decades, mortality trends have either increased, decreased or remained stable, depending on the geographical region under study. In Scotland, for example, mortality rates have risen, especially in the young.2 In Japan, mortality rates among males of all age groups have risen steadily.8 The sharpest increases have been observed in France, Germany, central and eastern Europe. In contrast, there has been a small decrease in mortality due to oral cancer in Ireland, Finland and the United Kingdom. In the United States, mortality rates declined by 22% from 1975 to 1991, perhaps due to earlier treatment for oral cancers.
On a worldwide basis, oral cancer incidence rates appear to have been stabilizing over the last decade, but the greater frequency of oral cancer in certain regions and among specific populations is a cause for concern. With this heightened awareness, research to further investigate the detection, diagnosis and prevention of oral cancer has recently been included as one of the targeted priorities supported by the National Institute of Dental and Craniofacial Research in the United States.9
Risk Factors
Age. The association of oral cancer with increasing
age is consistent with the disease process being related to environmental risk factors.
Risk rises dramatically from about 7 per 100,000 males at age 30 to approximately 80 per
100,000 for 60 year olds.3
Smoking and alcohol. An investigation of which factors might exert the most influence has shown that the use of tobacco and alcohol are major risk factors, implicated in about 75% of all oral cancers in the United States.10 Patterns of alcohol consumption, particularly among smokers, are also considered important. While heavy smoking or drinking each increase the risk of oral cancer, together their influence appears to be multiplicative.10 Perhaps the most striking effect for those who drink and smoke heavily is the increased risk for developing oral cancer - 38 fold for men and over 100 fold for women.10
The risk of oral cancer increases with the number of cigarettes smoked per day and the number of years that an individual smokes. No relationship was found between the age at which smoking began and the development of oral cancer.10 Tobacco use through cigar or pipe smoking also increases the risk for oral cancer, with the route of administration of tobacco and exposure to the carcinogenic compounds being related to the site of disease. For example, smokeless tobacco is linked to cancers of the cheek and gum. In Southeast Asia, where tobacco and Betel nut chewing is common, a greater number of oral cancers are seen.2 Cancer of the palate has been associated with smoking locally manufactured tobacco products in India.5
With regard to alcohol, the odds ratio for oral cancer increases proportionally with the amount consumed. For example, Japanese males consume 60% more alcohol than Japanese females, and have considerably higher oropharyngeal cancer mortality rates.8 The risk of oral cancer associated with wine consumption was the lowest for both men and women. The duration of alcohol ingestion, or age at onset of drinking was not largely correlated with the development of oral cancer.10
A
study from the United States indicated an elevated risk of oral cancer in mouthwash users
when the product contained an alcohol content greater than 25%,11 and duration
and frequency of use increases the risk. Leukoplakia, a common precursor to oral cancer,
is found more frequently in the oral cavities of those using high alcohol content
mouthwash.11 Follow-up research, however, has not confirmed these findings.
Loss of teeth. Edentulousness may indicate a greater risk for cancer of the gums. The need for dentures often precedes overt symptomatology of the cancer. Denture wearing itself, however, is not associated with an increased risk.11
New areas of investigation. Human papillomavirus (HPV), a well-known indicator of cervical cancer,12 has been detected in a number of oral squamous cell cancers in studies done in Germany, Japan, the Netherlands, South Africa, the United Kingdom and the United States.13 Both cervical and oral epithelia consist of similar squamous cell tissue, and it has been suggested that they may have a similar susceptibility to cancer.
There may also be a genetic component among the risk factors for oral cancer. Among certain groups in the United States, having a sibling with cancer (but not parents or offspring) was associated with an increased risk for developing oral cancer.6
Role of the Dental Care Provider in Reducing Risk Factors
Dentists and dental hygienists can help patients take action
against oral cancer. Since smoking and alcohol are the factors most commonly linked to
oral cancers, it is extremely important to recommend cessation or at least reduction in
the use of these agents. This is one of the most significant preventive measures
available.
A healthy diet can protect against oral cancer. Several studies from various regions of the world indicate that the inclusion of fresh fruit in the diet is associated with a reduced risk of oral cancer, and that supplementing the diet with vitamins A, C, and E (but not multivitamins) may exert a protective influence.15-17 The finding that HPV and certain genetic or early cellular changes may be associated with oral cancer is an interesting recent advance. It may be possible in the future to routinely screen the oral mucosa in patients at high risk for oral cancers, or identify patients with very early cellular changes. Mortality due to cervical cancers has decreased dramatically over the last few decades, primarily due to early detection and treatment. The promise of a similar available genetic test for early detection and treatment of oral cancers is an exciting prospect in this field.
Being aware of the risk factors for oral cancer, dental care providers are in a position to identify those patients who are most at risk, provide a thorough examination, and biopsy or refer any suspicious lesions found. Over time, these patients may be monitored more closely for the presence of leukoplakia. Recording a family history of cancer, smoking habits, diet and alcohol use is an important tool for identifying and following patients at risk.
Most importantly, the key course of action for preventing oral cancer lies in patient education. Keeping patients informed about risk factors for and protective measures against oral cancer will ultimately be the major tool for disease prevention. OC
References
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