Association of Smokeless Tobacco with Oral Cancer - Evidence From the South Asian Studies: A Systematic Review.

Smokeless tobacco (SLT) is associated with many heath hazards including oral cancer. Its use is more common in South Asian countries. The current paper aims to systematically review the South Asian studies to assess the association of SLT and oral cancer. Detailed automated literature searches of PubMed, Medline, EMBASE and ISI Web of Science from January 1980 to July 2015 were conducted using the key words "oral cancer", "oral precancer", "oral premalignant lesions", "oral squamous cell carcinoma", "smokeless tobacco", "betel quid", "areca nut", "Gutkha" in various combinations. Letters to the editor, review articles, and case-reports were excluded. Atotal of 21 studies were included. Three studies were of cohort design while the remaining were of case-control design. Nine studies reported betel quid as a risk factor for oral cancer, while fifteen studies reported data on other types of chewing tobacco. The odds ratio (OR) for betel quid and risk of oral cancer varied from 3.1 to 15.7 (11.0-22.1); and for chewable tobacco and risk of oral cancer varied from 1.2 (1.0-1.4) to 12.9 (7.5-22.3). Astrong association between different types of SLTand oral cancer was observed. Well-structured programmes should be employed in South Asian region, both in terms of educating the general public about the health hazards of SLTas well as providing cessation assistance.