In conclusion, this large collaborative pooled analysis of noncigarette tobacco use in 11 studies within PanC4 provides evidence that cigar smoking is associated with an excess risk of pancreatic cancer, while, based on small numbers, no signiﬁcant association emerged for pipe smoking and smokeless tobacco use.
Smokeless tobacco users who had never smoked (the relevant subgroup if we are to see whether SLT causes pancreatic cancer) was 0.62 (0.37-1.04).
Our results on smokeless tobacco use are in broad agreement with a recently published meta-analysis of all published data on the issue, which reported no excess risk of pancreatic cancer in case–control studies. They are, however, at variance with those from another meta-analysis, based mainly on data from two Nordic cohort studies, which suggested that smokeless tobacco is associated with an increased risk of pancreatic cancer.
Why the discrepancy? Partly because, as Brad Rodu and Philip Cole noted at the time, the two Nordic studies failed to control for drinking and smoking status. The widely reported claim that SLT results in a 67% increase in pancreatic cancer risk comes from one of these studies (also co-authored by Boffetta), but this was only achieved by including former smokers, who are known to have an increased risk. Amongst the non-smoking SLT users, there was no elevation in risk.
The new meta-analysis has addressed these confounding factors:
Further, we were able to allow for study design variables and major identiﬁed possible confounding factors, including ethnicity, education, BMI, diabetes and alcohol consumption, and to estimate the risk of smokeless tobacco use in lifelong nonsmokers, thus minimizing any possible bias due to residual confounding.
This study should go some way to finally putting the SLT/pancreatic cancer myth to bed. One by one, the scares about SLT, including Swedish snus, have been shown to based on remarkably little evidence. Although it is still widely believed that snus causes oral cancer, this has long-since been disproved by a string of studies (the EU removed the 'Causes Cancer' warning from snus back in 2001). In recent years, those opposing the legalisation of snus in the EU (Sweden has an exemption) have relied heavily on the pancreatic cancer scare. Although not biologically implausible, the epidemiological evidence for this has always been highly suspect and is at odds with population-level incidence of the disease (Sweden's rate of pancreatic cancer is the fourth lowest in the EU).
Health scares tend to cast long shadows, partly because studies like this go unreported in the media. It's possible that SLT will be popularly believed to cause oral and pancreatic cancer for years to come. But the evidence for both claims has never been weaker.