The relation between smokeless tobacco and cancer in Northern Europe and North America. A commentary on differences between the conclusions reached by two recent reviews

PN Lee Statistics and Computing Ltd, Surrey, UK.
BMC Cancer (Impact Factor: 3.32). 08/2009; 9:256. DOI: 10.1186/1471-2407-9-256
Source: PubMed

ABSTRACT Smokeless tobacco is an alternative for smokers who want to quit but require nicotine. Reliable evidence on its effects is needed. Boffetta et al. and ourselves recently reviewed the evidence on cancer, based on Scandinavian and US studies. Boffetta et al. claimed a significant 60-80% increase for oropharyngeal, oesophageal and pancreatic cancer, and a non-significant 20% increase for lung cancer, data for other cancers being "too sparse". We found increases less than 15% for oesophageal, pancreatic and lung cancer, and a significant 36% increase for oropharyngeal cancer, which disappeared in recent studies. We found no association with stomach, bladder and all cancers combined, using data as extensive as that for oesophageal, pancreatic and lung cancer. We explain these differences.
For those cancers Boffetta et al. considered, we compared the methods, studies and risk estimates used in the two reviews.
One major reason for the difference is our more consistent approach in choosing between study-specific never smoker and combined smoker/non-smoker estimates. Another is our use of derived as well as published estimates. We included more studies, and avoided estimates for data subsets. Boffetta et al. also included some clearly biased or not smoking-adjusted estimates. For pancreatic cancer, their review included significantly increased never smoker estimates in one study and combined smoker/non-smoker estimates in another, omitting a combined estimate in the first study and a never smoker estimate in the second showing no increase. For oesophageal cancer, never smoker results from one study showing a marked increase for squamous cell carcinoma were included, but corresponding results for adenocarcinoma and combined smoker/non-smoker results for both cell types showing no increase were excluded. For oropharyngeal cancer, Boffetta et al. included a markedly elevated estimate that was not smoking-adjusted, and overlooked the lack of association in recent studies.
When conducting meta-analyses, all relevant data should be used, with clear rules governing the choice between alternative estimates. A systematic meta-analysis using pre-defined procedures and all relevant data gives a lower estimate of cancer risk from smokeless tobacco (probably 1-2% of that from smoking) than does the previous review by Boffetta et al.

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    • "While the popularity of snus (low nitrosamine smokeless tobacco, Swedish type) is rapidly increasing in Northern Europe and in the USA, the potential role snus might have for public health is unclear. Based on systematic comparative analyses, it is agreed that use of snus is less dangerous than cigarettes for wellknown tobacco-related diseases (Gartner et al., 2007; Lee & Hamling, 2009; Royal College of Physicians, 2007; Scientific Committee on Emerging and Newly- Identified Health Risks, 2008). Thus, at a population level, a potential improvement in health can be obtained if adolescents who otherwise would have started to smoke cigarettes take up snus instead (Ramstrom & Foulds, 2006; Rodu & Cole, 2010), see Lund (2009) for a discussion. "
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    • "reported no increases among ST users for these diseases. The differences in these meta-analyses were thoroughly discussed in a separate commentary [7], which concluded that the risk of cancer from ST use is approximately 100-fold lower than that from smoking. The epidemiologic evidence is the basis for a growing consensus among tobacco research and policy experts that ST use involves far fewer health risks than smoking. "
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    ABSTRACT: It is now widely understood by tobacco research and policy experts that smokeless tobacco (ST) use confers significantly less risk than smoking, but no studies have assessed tobacco risk perceptions in highly educated populations. The purpose of this study was to explore the perception of risks related to smoking and ST use among full-time faculty on two campuses at the University of Louisville. In October 2007, a survey that quantified risk perceptions of cigarette smoking and ST use with respect to four health domains (general health, heart attack/stroke, all cancer, oral cancer) was sent to 1610 full-time faculty at the Belknap and the Health Sciences Center (HSC) campuses of the University of Louisville, and 597 (37%) returned a completed survey. Overall, cigarettes were considered as high risk for all health domains by large majorities (75-97%). Except for heart attack/stroke, ST was also considered as high risk by the majority of faculty (69-87%), and at least half perceived cigarettes and ST to be equally harmful across all domains. HSC faculty had somewhat more accurate risk perceptions than Belknap faculty for ST, but both groups overestimated the risks, especially for oral cancer. This study found that the risks of ST use are overestimated and conflated to that of cigarettes among highly educated professionals, demonstrating the need for better education about the risks of tobacco use and for communication of accurate information by health organisations and agencies.
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