Table 1 The characteristics of included studies and involved individuals
Study | Region | Study design | Sample size (case/non-case) | Age (yrs) | Sex (%) | Cases definition | Control definition | Type of smokeless product | Confounders adjusted | Matching of control | Study quality (NOS score) |
|---|---|---|---|---|---|---|---|---|---|---|---|
Hirayama 1966 [29] | Central and south east Asia | Case-control | 291 (173/118) | > 19.0 | Male and female | Hospital cases of oral cancer | Non cancer cases from hospital | Pan tobacco, Manpuri, and other (Chew) | Restricted to non smokers | Age and sex | 5 |
Winn 1981 [30] | US | Case-control | 643 (233/410) | All stages | Female | Hospital cases of oral cancer | Non cancer cases from hospital | Oral snuff (NonChew) | Analysis of non smokers | Age, race, source of ascertainment, and country | 6 |
Sankaranarayanan 1989a [31] | India | Case-control | 681 (228/453) | All stages | Male and female | Histologically confirmed cases of tongue and floor of mouth from HBCR | Two non cancer for each case from hospital | Pan tobacco chewer (Chew) | Restricted to non smoker among man and non smoking non alcoholic among women | Age, sex and religion | 7 |
Sankaranarayanan 1989b [32] | India | Case-control | 1082 (187/895) | All stages | Male and female | Cancer Cases of gingiva from PBCR | Non cancer cases from hospital | Pan tobacco/ (Chew) Snuff (Non Chew) | Bidi alcohol and other Tobacco type | Unmatched | 5 |
Nandakumar 1990 [33] | India | Case-control | 696 (348/348) | 55.0 | Male and female | Histologically confirmed cases registered in PBCR for lip, tongue and mouth | Non cancer cases from hospital | Mixed for Tobacco, Pan and snuff (Chew) | Restricted to Non Smoking | Sex, age gp and residential area | 6 |
Sankaranarayanan 1990 [34] | India | Case-control | 1309 (414/895) | All stages | Male and female | Cancer Cases of buccal mucosa and labial mucosa registered in Trivandrum HBCR (1983–84) | Non cancer cases from hospital | Pan tobacco/(Chew) Snuff (Non Chew) | Bidi, alcohol And other tobacco type | Unmatched | 6 |
Rao 1994 [35] | India | Case-control | 1348 (713/635) | 47.9 | Male | Histologically confirmed oral cancer cases from hospital | Non cancer cases from hospital | Mixed Pan, betel nut, lime tobacco (Chew) | Analysis in non smoker and non alcoholic, stratification for age and residence | Unmatched | 6 |
Lewin 1998 [36] | Sweden | Population based case referral oral cavity | 653 (103/550) | 40.0–79.0 | Male | Incident Case from PBCR | Population based controls | Oral moist snuff (Non Chew) | Age, region, smoking and alcohol | Age group and region | 7 |
Dikshit 2000 [37] | India | Case-control | 408 (148/260) | All stages | Male | From PBCR records | Population controls randomly selected | Tobacco quid (Chew) | Age and smoking | Unmatched | 6 |
Balaram 2002 [38] | India | Case-control | 1173 (591/582) | 18.0–87.0 | Male and female | Histologically confirmed cases cases of oral cancer | Non cancer cases from hospital | Pan tobacco (Chew) | Age centre education chewing and (men only) smoking and drinking habits | Frequency matched control by centre quinquennium of age and gender | 6 |
Znaor 2003 [39] | India | Case-control | 1879 (281/1598) | ≥ 25.0 | Male | Histologically confirmed cases cases of oral cancer | Non cancer cases from hospital | Tobacco type not specified (Chew) | Age, centre, education level and smoking and alcohol drinking center | Sex | 6 |
Luo 2007 [40] | Sweden | Retrospective cohort | 279,897 (248/279,649) | ≥ 35.0 | Male | Users of snus From 1969 through 1992 | Non users of snus | Swedish moist snuff (snus) (Non Chew) | Smoking | Not applicable | 7 |
Muwonge 2008 [41] | India | Nested case-control | 1692 (282/1410) | ≥ 35.0 | Male and female | Histologically confirmed Case that are newly | Randomly selected five non cancers from screened population | Pan with tobacco (Chew) Areca nut /lime +tobacco (Chew) | Smoking, alcohol education, religion | Sex, age panchayats and response status | 7 |
Jayalekshmi 2009 [42] | India | Prospective cohort | 78,140 (92/78,062) | 30.0–85.0 | Female | Former and current chewer females | Never chewer | Tobacco type not specified (Chew) | Age, family income, alcohol restricted to Non smokers | Not applicable | 8 |
Pednekar 2011 [43] | India | Prospective cohort | 87,222 (423/86,799) | ≥ 35.0 | Male | Male from voter list, cancer free at start. Patients registered in 150 government and private hospitals and institutions | Non user of SLT | Tobacco type not specified (Chew) | Age, education, religion, mother tongue, tobacco and BMI | Not applicable | 8 |
Jayalekshmi 2011 [44] | India | Prospective cohort | 66,277 (160/66,117) | 30.0–84.0 | Male | Former and current chewer females | Never chewer | Tobacco type not specified (Chew) | Age, calendar time, income and education | Not applicable | 8 |
Ray 2013 [45] | India | Case-control | 1250 (484/766) | 10.0–99.0 | Male and female | Histologically confirmed cases of oral cancer | Non cancer cases from hospital | (Betal + gudhaka) (Chew) Oral Snuff (Non Chew) | Restricted to Non Smokers and Non alcoholic | Area of residence | 6 |
Arain 2015 [46] | Pakistan | Case-control | 7556 (1401/6155) | 30.0–60.0 | Male and female | Histologically confirmed cases of oral cancer | Non cancer cases from hospital | Gutkha (Chew) NasalSnuff/(NonChew) Manipuri (Chew) | Smoking and Alcohol Other smokeless tobacco products (Restricted to non smoking and non alcoholic) | Age group, socio economic status and dietary habits | 6 |
Khan 2017 [47] | Pakistan | Case-control | 258 (84/174) | 57.0 | Male and female | Histologically confirmed cases of oral cancer | Non cancer cases from hospital | Naswar (Non Chew) | Age, sex, and MAS variables | Age, and sex | 5 |