Reprint requests to: Dr Rajesh Dikshit, Department of Pathology, Gandhi Medical College, Bhopal (MP), 462001, India.
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Abstract |
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Methods In all, 163 lung, 247 oropharyngeal and 148 oral cavity cancer cases from the Population-Based Cancer Registry records and 260 controls randomly selected from a tobacco survey conducted in the Bhopal population formed the study population.
Results A significant risk of bidi and cigarette smoking with a dose-response relationship was observed for lung and oropharyngeal cancer. Tobacco quid chewing showed no risk for lung, marginally increased risk for oropharyngeal and about a sixfold increased risk for oral cavity cancer. Population-attributable risk per cent (PARP) was observed to be 82.7% and 71.6% for smokers for the development of lung and oropharyngeal cancer, while the same was found to be 66.1% for tobacco chewers for the development of oral cavity cancer.
Conclusions These data provide strong evidence that smoking bidi is even more hazardous than cigarette smoking in the development of lung and oropharyngeal cancer. An intervention study to prevent the use of tobacco will be useful in this population as it also underwent gas exposure due to a chemical accident in 1984.
Keywords Bidi smoking, tobacco quid chewing, lung cancer, oropharynx cancer, oral cavity cancer
Accepted 10 January 2000
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Introduction |
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Two studies are available from India on the role of bidi smoking in the development of lung cancer.4,5 A few studies, mainly from West Maharashtra and South India, have reported the risk of oropharyngeal and oral cavity cancer and smoking and oral use of tobacco,6,7,8 but no study has been reported from central India.
In the present study three cancer sites (lung, oropharynx and oral cavity) were investigated using a common protocol and data from the Bhopal Cancer Registry. The risk of tobacco use, particularly bidi smoking and chewing, was estimated for these three sites. A study on tobacco use in this population is particularly important as it suffered exposure to methyl-isocyanate gas due to a chemical accident in 1984 and thus is different from other parts of the world.
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Materials and Methods |
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The cancer cases were coded by four-digit International Classification of Diseases for Oncology (ICD-O) code.9 The cancer sites included under oropharynx were posterior third of tongue (141.0 and 141.6), soft palate (145.3), uvula (145.4), oropharynx (146.0146.9), nasopharynx (147.0147.9), and hypopharynx (148.0149.0). The cancer sites included under oral cavity were lip (140.0140.9), anterior two-thirds of tongue (141.1141.5), gingivum (143.0143.9), floor of mouth (144.0144.9), cheek mucosa (145.0145.2), hard-palate and retromolar area (145.5145.9). A total of 260 controls were randomly sampled from a total of about 2500 males surveyed for tobacco habits in the Bhopal population. This tobacco survey was based on random samples from the voter list of the Bhopal municipal corporation area. The survey was conducted by the Bhopal cancer registry during 19891992. The controls were not matched for age with the cases, however, they were age-stratified and then randomly selected to follow the age distribution of cases.
The cases and controls were interviewed according to a precoded questionnaire. The subjects were asked about identification particulars, socioeconomic parameters, tobacco habits, and clinical history. The interview was conducted by three qualified social workers of the Cancer Registry staff. The cases for which detailed information about smoking or chewing history were not available were excluded from the study. Cases registered from death certificates were excluded. Similarly, the tongue not otherwise specified cases (141.9) were not included in the analysis. After exclusion, a total of 163 lung, 247 oropharyngeal and 148 oral cavity cancer cases were available for the analysis.
The data collected were compiled and quality checks were carried out. Age-adjusted odds ratio (OR) and 95% CI for the sites under study according to religion, educational status, smoking and chewing habits were estimated using unconditional multiple logistic regression models. The models were compared using the differences in deviance and in degrees of freedom. The result of variable of interest with and without confounding variable was tabulated. The effect of interaction between variable of interest and confounder were also obtained to understand the validity of adjustment. The dummy variable and linear dose-response model was compared for testing the extent to which the linear trend adequately explains the variation between the dose level.10 The population attributable risk and attributable risk of individuals exposed to exposure of interest were also estimated. For model fitting, the statistical program GLIM was used.11
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Results |
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Discussion |
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Religion and educational status were not observed to be risk factors in the present study. A study of the association of religion and smoking habits with lung cancer likewise did not observe any excess risk for different religion.5 Both bidis and cigarettes were found to be independently associated with increased risk of lung and oropharynx cancer. Two previous studies on the risk of lung cancer among bidi smokers have shown conflicting results. Notani and Sanghavi,4 taking hospital controls, found a relative risk of 2.6, while Jussawalla and Jain,5 taking community controls, found a relative risk of 19.3 in comparison to non-smokers. Similar to the present study increased risk for oropharyngeal cancer among bidi smokers was observed in a previous study.6
The observed OR for bidi and cigarette smoking combined (OR = 24.1 for lung and OR = 6.2 for oropharynx) in comparison to non-smokers of both was much lower than expected, indicating that either mode of action is not multiplicative or those smoking both bidis and cigarettes are light smokers of each. The risk estimates further revealed that smoking bidi is even more hazardous than cigarette smoking in the development of lung and oropharyngeal cancer (Table 4).
The Indian bidi contains only a small amount of tobacco dust rolled in a dried leaf of tendu (Diospyrous malanoxylon) or Temburni tree (Diospyrous ebenum).12 In comparison to US cigarettes, the mainstream smoke of bidi contains a much higher concentration of several toxic agents such as hydrogen cyanide, carbon monoxide, ammonia, other volatile phenols, and carcinogenic hydrocarbons such as benz(a)anthracene and benzopyrene. Bidi also delivers more nicotine than Indian cigarettes. The nitrosonornicotine (NNN) and 4(methyl-nitrosoamino)-1-(3-pyridol) (NNK) level of bidi tobacco ranged from 6.2 to 12 µg/g compared with 1.3 to 58.0 µg/g in cigarette tobacco.13 Further, bidi smokers were found to take almost five puffs per minute compared to the cigarette smokers who smoked two puffs per minute.12 Thus, higher yields of tobacco-specific nitrosamines (TSNA) and higher puffing frequency among bidi smokers suggest that the finding of the present study, that the risk for development of lung and oropharyngeal cancer is higher among bidi smokers, is biologically plausible. The effect of smoking differed according to cell type of lung cancer. The risk was highest for squamous cell carcinoma. While the risk of smoking was lowest for developing adenocarcinoma, it was still high (OR = 3.9). These results are consistent with the result of other workers.14,15
Chewing tobacco contains a high level of TSNA.13 Of these, for NNK and its reduction product 4-(methyal(nitrosoamino)-1-1(3-pyridyl)-1-butanol) (NNAL) the major target organ is the lung, especially the peripheral part of the lung. This is independent of the route of admission, whether these procarcinogens are applied topically to the skin, taken orally or by intraperitoneal injection.16,17 These experimental studies suggest that tobacco chewing may also enhance the risk of lung cancer. The present study, however, did not observe any increased risk of tobacco chewing for lung cancer. The increased risk for oral cavity cancer among tobacco chewers is in accordance to that observed by other workers.7,8,18 These risk estimates in the present study could not be adjusted for the use of alcohol as history of alcohol use was not taken in the Cancer Registry proforma. However, this does not seem to alter the risk of tobacco chewing to a great extent. In India the prevalence of alcohol consumption particularly relative to tobacco chewing is low. Studies from India have not observed excess risk for oral cancer among alcohol users.7,8 The interaction model presented in Table 7 gave an indication that the mode of action of tobacco quid chewing and smoking may not be multiplicative. It further indicated a decline in risk of chewing of tobacco with increased amount of tobacco smoked, this may be because heavy smokers chew less than light smokers.
In India cross-sectional surveys have shown that the percentage of people who chew betel quid without tobacco is small. In the present study also, based on small numbers, elevated risk was observed for oral cavity cancer among chewers not using tobacco, a finding similar to another study from south India.8
Tobacco consumption has decreased in many developed countries while in most developing countries it is still increasing. This may largely be due to the fact that relatively fewer studies have been reported from developing countries, including India, on the risk of cancer at different cancer sites due to the use of various forms of tobacco.19 In the present study it was estimated that the population attributable risk per cent (PARP) for smoking was quite high for lung (82.7%) and oropharyngeal cancer (71.6%). Similarly, the PARP was found to be 66.1% for tobacco chewers for development of oral cavity cancer. The attributable risk among smokers was observed to be 92% and 85% for lung and oropharyngeal cancer, respectively. The attributable risk for those who chewed tobacco was 84.4% for development of oral cavity cancer. This suggests that the high percentage of lung, oropharyngeal and oral cavity cancers in Bhopal could be prevented if tobacco habits were not started. Intervention studies encouraging quitting tobacco use have much relevance in Bhopal as in this population lungs are already damaged to some extent due to exposure to methyl isocynate gas as a result of the chemical disaster in December 1984. Even if gas exposure proves to be carcinogenic in future, by preventing the use of tobacco, a large number of cancer cases could be prevented.
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Acknowledgments |
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Notes |
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References |
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