A review published in The Lancet Oncology finds that although users of smokeless tobacco products (STPs) likely have a lower cancer risk than smokers, they are still increasing their risk of developing several types of cancer.

In the USA and Sweden, a finely cut or powered, flavored tobacco called moist snuff is the most popular form of STP used. In places like India, there is a wide range of products that are regularly consumed. These STPs contain over 30 carcinogenic (cancer-promoting) compounds, such as nitrosamines and metals. To investigate STPs and cancer risk, Dr Paolo Boffetta (International Agency for Research on Cancer (IARC), Lyon, France) and colleagues studied global STP use – both oral and nasal varieties – and the risk of cancer associated with them.

Researchers still lack conclusive evidence as to the risk of individual cancers due to STPs. For example, American and Asian studies have found a 2.5 times increase in oral cancer for STP users, but similar European studies were unable to find a significant increase in risk. Boffetta and colleagues performed an assessment of all studies and concluded that STPs lead to an 80% increase in risk of oral cancer, a 60% increase in risk of esophageal cancer, and a 60% increase in risk of pancreatic cancer. There also seem to be geographic differences in how these specific cancers are related to STP use. More than 50% of oral cancers in India and Sudan can be attributed to STPs specific to those countries, compared to only 4% of oral cancers in the USA. Sweden can blame 20% of esophageal and pancreatic cancer on STPs that are consumed there.

Lung cancer research has also resulted in inconsistencies across geographical areas. Studies from northern Europe have not found an increased lung cancer risk due to STPS, but research from the USA suggests an 80% increase in lung cancer risk for STP users.

One study included in the analysis assesses the change in cancer risk for two groups of men: one that quit smoking and switched to spit tobacco (switchers) and another that quit smoking and any tobacco use completely (quitters). Those who continued using tobacco, the switchers, had about a 2.5 times increase in risk of death from oral cavity and pharynx cancers than those who stopped using tobacco. The relative risk of lung cancer, compared to quitters, was 50% higher for switchers who used chew only, 90% higher for switchers who used snuff only, and 100% higher for switchers who changed to chew and snuff. The study also revealed that the quitters were four times as likely, and the switchers more than 5.5 times as likely, to develop lung cancer compared to men who never used tobacco products.

According to the authors, there is strong support from animal studies and research on cancer mechanisms that indicates an increase in cancer risk due to STPs. “We do not intend to address explicitly the use of smokeless tobacco to reduce the risk from tobacco smoking – e.g., by promoting smokers to switch to smokeless products or by introducing these products in a population where the habit is not prevalent. Nevertheless, several conclusions can be reached based on the available data…the risk of cancer, especially that of oral and lung cancer, is probably lower in smokeless tobacco users in the USA and northern Europe than in smokers, and the risk of cancer is higher in smokeless tobacco users than in non-users of any form of tobacco. Available data for a possible benefit of switching from smoking to smokeless tobacco come from few studies and models from the USA and Sweden. Comparative risk estimates depend on many assumptions, including the expected effect of the introduction of new smokeless products in populations where the habit has not been common,” they conclude.

Smokeless tobacco and cancer
Paolo Boffetta, Stephen Hecht, Nigel Gray, Prakash Gupta, Kurt Straif
The Lancet Oncology
(2008). 9(7): pp. 667-675.
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Written by: Peter M Crosta