Risk of major cancers associated with various forms of tobacco use in India: a systematic review and meta-analysis

Abstract

Several studies have established the association of various cancers with tobacco consumption. However, hardly any attempt has been made to examine the combined effect of various forms of tobacco consumption. Hence, the present study was undertaken to measure the overall risk of different cancer sites associated with various forms of tobacco used individually or in combination, and to investigate the risk variation within each site by different forms of use. Meta-analysis was carried out on the findings of 22 published studies of samples exposed to tobacco use and control groups that were not exposed to tobacco. The pooled odds ratios (ORs) for each cancer for different combinations of forms of tobacco were calculated using a random effects model. Smoking was found to be associated with a 5-fold higher risk of oropharynx, larynx, and lung, a 3-fold higher risk of hypopharynx, and esophagus, and a 2-fold higher risk of oral cancer. Esophagus (OR = 3.5) and oral cancer were the only sites significantly associated with tobacco chewing. The OR associated with bidi smoking was highest for lung (6-fold) followed by esophagus (3.5-fold) and oral cancer (3-fold). Lung cancer was also significantly associated with cigarette smoking. The present study reported pooled ORs for different tobacco-related cancers associated with various forms of tobacco use, both individually as well as in various combinations. Collecting data on the consumption of tobacco is a complex exercise. Pooled ORs reported in this study will be useful in working out the quantum of diverse tobacco-related cancers attributable to different forms of tobacco consumption, both individually as well as in combination.