Smokeless tobacco: association with increased cancer risk.

Smokeless tobacco (chewing tobacco and snuff) contains known carcinogens shown to increase the risk for oral cancer. The effect of snuff has been more fully documented than other forms of smokeless tobacco, although the carcinogenic potential of all such products is acknowledged. Risk increases with increasing length of exposure, with risks greatest for anatomic sites where the product has been held in contact the longest time. In some studies, other organs, such as the esophagus, larynx, and stomach, have been shown to be at increased risk for cancer from the use of smokeless tobacco, although at present the data are insufficient to substantiate fully a causal association. Numerous reports have shown an association between snuff use and leukoplakia, with less evidence at present linking chewing tobacco use with leukoplakia. The documented early onset of the smokeless tobacco habit and reports of increases in certain oral cancers among young men raise serious concerns of an impending oral cancer epidemic in this population. In addition, synergistic interactions with other oral cancer risk factors, e.g., smoking and alcohol, and a high rate for second primaries observed for these cancers add to the concern. Unless the tide of its use is stemmed, long-term use can be expected to produce an increase in oral cancers, and perhaps cancers of other sites, as youthful users mature and accumulate exposure to this carcinogenic agent.