First of all, risk is a complicated concept, so it is vital to understand all the information that is contained in a risk estimate. It starts with an incidence rate, which is the number of new cases of a disease that is seen in a population over a specified period of time. The Surveillance Epidemiology and End Results (SEER) program at the National Cancer Institute has collected information on incidence since 1973.
SEER data reveals that there were about 34 cases of oral/throat cancer annually among 100, 000 men ages 40-84 years from 2001 to 2006. This is an overall rate, which can be apportioned among the following groups: men who have not been exposed to known causes of oral cancer, current smokers, former smokers and alcohol abusers.
Non-exposed men make up about 45% of the population, and they have the baseline rate of oral/throat cancer (the relative risk, RR = 1.0). Current smokers make up about 25% of the population, and their RR for oral/throat cancer is eleven, compared with non-exposed men. Former smokers also comprise 25% of the population and have an RR of 3.4. Alcohol abusers comprise the remaining 5% and have an RR of 4.0. The overall incidence rate of 34 per 100, 000 men per year is apportioned among the following groups:
|Oral/Throat Cancer Among Men Age 40-84 Years Old in the U.S., 2001-2006|
|Exposure Group||Rate (cases per 100, 000 men per year)|
What does this mean to the individual male user of moist snuff or chewing tobacco?
Dr. Philip Cole and I reviewed oral/throat cancer risks among smokeless tobacco users (abstract here) in 2002. We found that users of moist snuff (including snus) and chewing tobacco did not have risks that were significantly higher than those of nonusers of tobacco. Our findings were confirmed by a comprehensive meta-analysis of all epidemiologic studies of smokeless tobacco use and cancer (discussed by me here).
This exercise reveals that there are 3.6 cases of oral cancer among 100, 000 smokeless tobacco users each year (or 36 cases among a million users), the same rate seen in non-exposed men. While it is not “zero” risk, it is no higher than the risk among men who are neither smokers nor heavy drinkers.
The concept of individual risk is also applicable to those individuals who believe they developed oral cancer due to smokeless tobacco use. Many such cases have become causes célèbres among anti-tobacco groups and the media. While all instances of cancer are distressing, associating one’s disease with a specific cause is highly problematic. Claims of causation should be examined objectively.
Scientific research has documented that cases of oral cancer associated with powdered dry snuff occur after decades of use. In one of the largest case series, powdered dry snuff users with oral cancer were on average 78 years old and had used the product for 55 years. Science may not support those oral cancer victims who blame smokeless tobacco for their condition if they used the product for less than two decades or developed cancer at a young age.
An objective investigation of a smokeless tobacco claim would consider other risk factors as well. Did the individual also smoke or use alcohol excessively? Has the person had a human papillomavirus (HPV) infection, which is now recognized as a cause of oral/throat cancer? These are important risk factors for oral cancer that should not be overlooked.
Finally, virtually everyone is at risk, however small, for every disease. Although oral cancer is rare, it most commonly occurs in smokers and/or heavy drinkers who are 50 years or older. However, as an oral pathologist, I have diagnosed oral cancer in 25-year-olds who didn’t smoke or drink.