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: 3.36). 08/2009; 9(1):256. DOI: 10.1186/1471-2407-9-256
Source: PubMed


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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    Addiction Research and Theory 12/2012; 20(6):447-455. DOI:10.3109/16066359.2012.665521 · 1.03 Impact Factor
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    • "Cleaner forms of smokeless tobacco have been estimated to be 90–95% less harmful than cigarettes when used long term [4], and some contend they may be even less harmful [5]. Recent research syntheses suggest that the difference in estimates is largely a function of the attributed risk for heart disease and stroke [6-8], as it now appears that there is little or no excess cancer risk [9,10]. If as seems prudent, one assumes the current epidemiology which suggests an elevated risk of both heart disease and stroke [6-8], then the lower estimate is the most plausible. "
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    Harm Reduction Journal 06/2012; 9(1):19. DOI:10.1186/1477-7517-9-19 · 1.26 Impact Factor
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    • "Table 1 shows the major differences in risk estimates between the meta-analyses of Boffetta and that of Lee-Hamling for cancers of the oral cavity, esophagus and pancreas. A detailed subsequent analysis published by Lee and Hamling [5] revealed that the differences were due to the following factors: (a) Boffetta et al. did not use all available studies, and there were no specific criteria for which studies were included and which were excluded; Lee and Hamling used all available studies. (b) in some instances Boffetta et al. used only the highest risk estimates, even though they were derived from internally inconsistent subgroups of either ST exposure or of the disease outcome of interest; Lee and Hamling's analysis was conducted with clear and consistent criteria for ST exposure and disease outcomes [5]. "
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    Harm Reduction Journal 07/2011; 8(1):19. DOI:10.1186/1477-7517-8-19 · 1.26 Impact Factor
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