The use of smokeless tobacco products (STPs) increases the risk of a range of cancers. But people who use STPs probably have a lower overall cancer risk than those who smoke. The issues are discussed in the July edition of The Lancet Oncology.

Dr Paolo Boffetta International Agency for Research on Cancer (IARC) Lyon France and colleagues looked at global patterns of STP use, oral and nasal, and the risk of cancer associated with them. Moist ‘snuff’—a finely cut or powdered flavoured tobacco—is the most popular form consumed in the USA and Sweden whilst in India a wide variety of products exists. More than 30 carcinogens exist in STPs including nitrosamines and metals. With respect to individual cancers controversy exists as to the risk posed by STPs. Studies from the USA and Asia suggest the risk of oral cancer was increased by more than two-and-a-half times but similar studies from Europe suggest no increased risk.

Combining all studies shows an overall increased risk of oral cancer of 80% for STP users. The overall increased risk for cancer of the oesophagus was 60% and for pancreatic cancer also 60% for STP users. Results on lung cancer have been inconsistent with northern European studies suggesting no excess risk, yet USA based studies showing an increased risk of 80% for STP users. Relative cancer burdens also vary extensively between countries. In India and Sudan more than 50% of oral cancers are attributable to STPs used in those countries, while this proportion in the USA is 4%. In Sweden 20% of oesophageal and pancreatic cancers are attributable to STPs.

The authors also reviewed the data from one study on changing cancer risk for men switching from cigarette smoking to use of spit tobacco (switchers), with men who quit using tobacco entirely (quitters). Switchers had around a two-and-a-half times increased mortality risk from oral cavity and pharynx cancers than quitters. Compared with quitters the relative risk of lung cancer was increased by 50% for switchers to chew only, 90% for snuff only and 100% for chew and snuff combined. Compared with men who never used any tobacco product the relative risk of lung cancer was nearly four times higher for quitters and over five-and-a-half times higher for switchers.

The authors say that animal experiments and studies on mechanisms of cancer strongly support the notion of carcinogenicity of STPs. They do not recommend smokeless tobacco as a substitute for smoking and conclude: “We do not intend to address explicitly the use of smokeless tobacco to reduce the risk from tobacco smoking—eg 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.”