Meta-analysis of the relation between European and American smokeless tobacco and oral cancer

Following literature review a meta-analysis was conducted of 32 epidemiological studies published between 1920 and 2005 including tests for homogeneity and publication bias.Based on 38 heterogeneous study-specific estimates of the odds ratio or relative risk for smokeless tobacco use, the random-effects estimate was 1.87 (95% confidence interval 1.40–2.48). The increase was mainly evident in studies conducted before 1980. No increase was seen in studies in Scandinavia. Restricting attention to the seven estimates adjusted for smoking and alcohol eliminated both heterogeneity and excess risk (1.02; 0.82–1.28). Estimates also varied by sex (higher in females) and by study design (higher in case-control studies with hospital controls) but more clearly in studies where estimates were unadjusted, even for age. The pattern of estimates suggests some publication bias. Based on limited data specific to never smokers, the random-effects estimate was 1.94 (0.88–4.28), the eight individual estimates being heterogeneous and based on few exposed cases.Smokeless tobacco, as used in America or Europe, carries at most a minor increased risk of oral cancer. However, elevated risks in specific populations or from specific products cannot definitely be excluded.Oral cancer, histologically most frequently squamous-cell carcinoma, includes malignant neoplasms of the lip, tongue, palate, gum, piriform sinus, floor of the mouth, pharynx, tonsils, salivary glands and unspecified parts of the mouth [1]. It is the eighth and 14th most incident cancer worldwide in men and women, respectively [2]. Age-standardised mortality rates (per 100,000 per year) differ regionally, ranging (in 2001) from 2.4 in Sweden to 21.2 in Hungary. Trends differ also, with, in the past two decades, decreases in the US, Finland and Sweden, and increases in Hungary, the Czech Republic, Germany and Norway [3,4]. US mortality rates are higher in blacks than whites, and prevalence is greater in areas with a high proport