A study of betel quid carcinogenesis. II. Formation of N-nitrosamines during betel quid chewing

In model studies, nitrosation of the major areca alkaloid, arecoline, leads to the formation of N-nitrosoguvacoline, 3-(methylnitrosamino)propionitrile (MNPN), 3-(methylnitrosamino)propionaldehyde and two unknown N-nitrosamines. MNPN is a strong carcinogen in Fischer 344 rats. After subcutaneous injection of 1.1 mmol MNPN in 60 doses, all 15 male and 15 female rats developed tumours within 24 weeks; multiple tumours occurred in 26 of the rats. Eighty-seven percent of the animals had tumours of the oesophagus, 70% had nasal cavity tumours, 37% had tumours of the tongue, 7% tumours of the pharynx and 7% tumors of the forestomach. At the dose used, male and female rats showed no significant difference in tumour incidence or site of tumours. The formation of MNPN during betel quid chewing, although likely, has not yet been proven, while the areca-derived N-nitrosamine, N-nitrosoguvacoline (NG), has been found in the saliva of betel quid chewers at levels of 2.2-348 micrograms/L. N-Nitrosoguvacoline levels were higher in the saliva of chewers who used betel quid together with tobacco. The saliva of these chewers also contained tobacco-specific N-nitrosamines.     

A study of betel quid carcinogenesis. 3. 3-(Methylnitrosamino)-propionitrile, a powerful carcinogen in F344 rats

3-(Methylnitrosamino)propionitrile (MNPN) is formed in vitrounder mild nitrosation conditions from the major areca alkaloidarecoline. It appears likely that MNPN is generated during betelquid chewing especially when tobacco is added to the quid. Uponsubcutaneous injection of 1.1 mmol of MNPN in 60 subdoses, allof the 15 male and of the 15 female F344 rats developed tumorswithin 24 weeks. Twenty-six of the rats had tumors in two differentorgans at least. Twenty-seven rats had esophageal tumors, 21nasal tumors, 11 had tongue tumors and two animals had eitherpharyngeal carcinomas or papillomas of the forestomach. No tumorswere observed in the solvent control group. These data indicatethat MNPN is a potent carcinogen.     

The role of N-(nitrosomethylamino)propionitrile in betel-quid carcinogenesis

N-(Nitrosomethylamino)propionitrile (NMAP) was isolated and identified in the saliva of betel-quid chewers in amounts ranging from 0.5 to 11.4 micrograms/l. Groups of 21 male and 21 female rats were given 60 subcutaneous injections of NMAP over a 20-week period (total doses, 0.055 and 0.23 mmol/rat). After 106 weeks, the higher dose had induced 18 (86%) malignant tumours of the nasal cavity in male and 15 (71%) in female rats. Nine (43%) liver tumours were observed among animals treated with the lower dose. Fischer 344 rats were treated with a single dose of NMAP (intravenously or subcutaneously, 0.4 mmol/kg; or by swabbing the oral cavity, 2.21 mmol/kg), and the levels of N7-methylguanine (7-meG) and O6-methylguanine (O6-meG) were measured in DNA isolated from oesophagus and nasal mucosa, which are target organs, and from liver which is not. Higher levels of O6-meG and 7-meG were detected in the nasal mucosa and lesser DNA methylation in the liver and oesophagus, independent of the mode of administration. This correlates with the results of the study of the tumorigenic properties of NMAP in rats.     

Comparative tumorigenicity and DNA methylation in F344 rats by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosodimethylamine

The tumorigenic activities and DNA methylating abilities in F344 rats of the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and the structurally related nitrosamine N-nitrosodimethylamine (NDMA) were compared. Groups of 30 male rats were given 60 s.c. injections of 0.0055 mmol/kg of either NNK or NDMA over a 20-week period (total dose, 0.33 mmol/kg). The experiment was terminated after 104 weeks. The numbers of rats with tumors were as follows for NNK and NDMA, respectively: liver, 10 and 6; lung 13 and 0; and nasal cavity, 6 and 1. NNK was significantly more tumorigenic than was NDMA toward the lung (P less than 0.01) and nasal cavity (P less than 0.05). Groups of rats were treated with a single s.c. injection of 0.39 mmol/kg or 0.055 mmol/kg of NNK or NDMA and the levels of 7-methylguanine and O6-methylguanine were measured in liver, lung, and nasal mucosa 1-48 h after treatment. In liver and lung, levels of 7-methylguanine and O6-methylguanine in DNA were 3-22 times (P less than 0.001) greater in NDMA treated rats than in NNK treated rats. Levels of methylation induced by NDMA and NNK in the nasal mucosa were similar. The results of this study demonstrate that NNK is a more potent tumorigen than NDMA in the F344 rat and suggest that DNA methylation alone does not account for its strong tumorigenicity in rat lung and nasal mucosa.     

A study of betel quid carcinogenesis. 1. On the in vitro N-nitrosation of arecoline

Betel quid chewing is strongly associated with cancer of theoral cavity. Extracts of betel quid are tumorigenic in the experimentalanimal, but thus far, not a single carcinogen has been detectedin the tobacco free quid. This study is based on the hypothesisthat during chewing, arecoline, the major alkaloid of the betelnut, gives rise to carcinogenic N-nitros-amines. In vitro experimentsreported here have shown that N-nitrosation of arecoline leadsto N-nitrosoguvacoline (NG), 3-(methylnitrosamino)propionitrile(MNPN) and 3-(methyI-nitrosoamino)propionaldehyde. Although,according to an earlier study, NG is most likely not carcinogenic,MNPN is suspected to be a relatively strong animal carcinogenbased on bioassays with its lower homologue. The conditionsprevailing in the oral cavity of betel quid chewers are likelyto favor the formation of these three nitrosamines.     

A study of betel quid carcinogenesis--VIII. Carcinogenicity of 3-(methylnitrosamino)propionaldehyde in F344 rats.

In assays of Areca-specific N-nitrosamines, 3-(methylnitrosamino)propionaldehyde (MNPA) exhibits higher cytotoxicity than nitrosoguvacine (NGC), nitrosoguvacoline (NG) and 3-(methylnitrosamino)propionitrile (MNPN). NGC is not mutagenic. However, NG is a weak carcinogen in F344 rats while MNPN is a potent carcinogen; MNPA had thus far not been tested. In this study MNPA was injected s.c. at a dose of 6.57 mg three times weekly for 15 weeks (total dose 2.6 mmol/rat). During the 100 weeks of the bioassay, the treated F344 rats, and especially the females, showed significantly less weight gain than the control animals, indicating high toxicity for MNPA at the tested dose. Upon termination of the bioassay, the MNPA-treated animals were found to have tumors of the lung, liver, nasal cavity, forestomach and kidneys. The control animals showed no tumors in these organs. The incidence of lung tumors in the MNPA group was statistically significant (P less than 0.025). The results of this study show that MNPA is a carcinogen in F344 rats.     

Chromosome-damaging activity of saliva of betel nut and tobacco chewers

Saliva of volunteers chewing betel quid, cured betel nut (Areca catechu), betel leaves (Piper betle), a mixture of quid ingredients (dried betel nut flakes, catechu, cardamon, lime, copra and menthol) and Indian tobacco was collected and examined for its genotoxic activity. Chromosome aberrations (chromatid breaks and chromatid exchanges) in Chinese hamster ovary (CHO) cells were used to estimate the genotoxic effect. No detectable levels of clastogenic activity were observed in the saliva of non-chewing individuals. After 5 min of chewing betel quid, betel nut, betel leaves, quid ingredients and Indian tobacco, the saliva samples showed relatively potent clastogenic activities. The addition of transition metals Mn²⁺ and Cu²⁺ to the saliva samples of betel nut and Indian tobacco chewers enhanced their clastogenic activities, whereas Fe³⁺ increased the clastogenicity of the betel nut saliva but decreased the genotoxic effect of the saliva of Indian tobacco chewers. After removal of the betel quid or its components from the mouth, the clastogenic activity disappeared within 5 min. The western-type chewing tobacco did not produce a genotoxic activity in the saliva of chewers. A possible association between the genotoxicity in the saliva of betel quid chewers and the development of oral, pharyngeal and esophageal carcinomas is discussed.     

Oral lesions, genotoxicity and nitrosamines in betel quid chewers with no obvious increase in oral cancer risk

A link between the generation of areca nut-related N-nitrosamines in the saliva, the induction of genotoxic damage in the oral mucosa, as judged by an increase in micronucleated exfoliated cells (MEC), and a low incidence of oral cancer was studied in 2 population groups characterized by their habit of chewing quids without tobacco: Guamanians, who chew areca nuts (Areca catechu) with or without the addition of betel leaf (Piper betle); Taiwanese, who use areca nut, betel leaf or inference and slaked lime. The levels of N-nitrosoguvacoline (NG) in the saliva of chewers of fresh green areca nuts were very high (70.8 ng/ml) as compared to those reported for individuals using the more complex Indian betel quids (0.91 ng/ml or 5.6 ng/ml). None of the other areca nut-related nitrosamines (N-nitrosoguvacine (NGC), 3-(methylnitrosamino)propionitrile (MNPN) and 3-(methylnitrosamino)propionaldehyde (MNPA)) were detected in the saliva of Taiwanese betel quid chewers. The addition of slaked lime to the areca nut enhances the formation of NG during a chewing session. The frequency of MEC did not increase in the oral mucosa of areca nut chewers who do not use slaked lime, but showed a small but significant elevation in individuals using lime-containing quids. The elevation of MEC in Taiwanese, who are at low risk for oral cancer, is relatively small as compared to that found in chewers of Indian betel quids (pan), who show a highly elevated oral cancer risk. The results seem to suggest that NG may play only a minor role, if any, in the etiology of oral cancer among betel quid chewers.     

Tobacco-specific and betel nut-specific N-nitroso compounds: occurrence in saliva and urine of betel quid chewers and formation in vitro by nitrosation of betel quid

In order to evaluate exposure of betel quid chewers to N-nitrosocompounds, saliva and urine samples were collected from chewersof betel quid with or without tobacco, from tobacco chewers,from cigarette smokers and from people with no such habit, andwere analysed for the presence of N-nitrosamines by gas chromatographycoupled with Thermal Energy Analyzer and alkaloids derived frombetel nut and tobacco by capillary gas chromatography fittedwith nitrogen-phosphorous selective detector. The levels ofthe betel nut-specific nitrosamines, N-nitrosoguvacoline andN-nitrososoguvacine (the latter being detected for the firsttime in saliva), ranged from 0 to 7.1 and 0 to 30.4 ng/ml, respectively.High levels of tobacco-specific nitrosamines were detected inthe saliva of chewers of betel quid with tobacco and in thatof chewers of tobacco, ranging from 1.6 to 59.7 (N'-nitrosonornicotine),1.0 to 51.7 (N'-nitrosoanatabine) and 0 to 2.3 [4-(methyl-nitrosamino)-1-(3-pyridyl)-l-butanone]ng/ml. Urinary concentrations of certain N-nitrosamino acids,including N-nitrosoproline, were determined as a possible indexof exposure to nitroso compounds and their precursors in thestudy groups: no clear difference was observed. The betel nut-specificalkaloid, arecoline, was present at high levels in the salivaof betel quid chewers with or without tobacco. Nicotine andcotinine were also detected in saliva and urine of chewers oftobacco and of betel quid with tobacco. In order to assess whetherN-nitroso compounds are formed in vivo in the oral cavity duringchewing or in the stomach after swallowing the quids, the levelsof N-nitroso compounds in betel quid extracts were determinedbefore and after nitrosation at pH 7.4 and 2.1. The resultsindicate that N-nitroso compounds could easily be formed invivo. The possible role of N-nitroso compounds in the causationof cancer of the upper alimentary tract in betel quid chewersis discussed.     

Synthesis and kinetics of decomposition of 7-(2-cyanoethyl)guanine and O6-(2-cyanoethy)guanine, markers for reaction of acrylonitrile and 3-(methylnitrosamino)propionitrile with DNA

Acrylonitrile, a carcinogen in rodents, is used in the large-scaleproduction of acrylic polymers. 3-(Methylnitrosamino)propionitrile,a potent carcinogen in Fischer rats, is an Areca-derived nitrosaminewhich has been found in the saliva of betel quid chewers. Uponmetabolic activation, both of these carcinogens can react withDNA to form 7-(2-cyanoethyl)guanine and O⁶-(2-cyanoethyl)guanine.The latter has never been described. We have therefore synthesizedthis derivative by reacting 2-(N-carbethoxy-N-nitrosamino)propionitrilewith deoxyguanosine.     

Cyanoethylation of DNA in vivo by 3-(methylnitrosamino)propionitrile, an Areca-derived carcinogen

2-Cyanoethyldiazohydroxide is a likely product of metabolic alpha-hydroxylation of 3-(methylnitrosamino)propionitrile (MNPN). The reaction of 2-(N-carbethoxy-N-nitrosamino)propionitrile, a stable precursor of 2-cyanoethyldiazohydroxide, with deoxyguanosine, catalyzed by porcine liver esterase, was investigated. Two major deoxyguanosine adducts were produced. They were isolated by high-performance liquid chromatography and characterized by their UV spectra, mass spectra, and proton magnetic resonance spectra. On the basis of these spectral data, the structures of the two adducts were assigned as 7-(2-cyanoethyl)guanine and O6-(2-cyanoethyl)deoxyguanosine. The potential of MNPN to cyanoethylate DNA in F344 rats was evaluated by measuring 7-(2-cyanoethyl)guanine and O6-(2-cyanoethyl)guanine in the liver, nasal mucosa, and esophagus. The highest levels were detected in the nasal cavity, which is one of the major target organs for the carcinogenic effects of MNPN.     

Organ and cell specificity of DNA methylation by N-nitrosomethylamylamine in rats

N-Nitrosomethylamylamine (NMAA) is a potent carcinogen in rodents with the esophagus as the principal target organ. The present study aims at an assessment of DNA methylation by NMAA in various rat tissues and an identification of cell populations actively involved in its bioactivation. Adult male F344 rats received a single i.p. dose of N-nitroso[methyl-14C]amylamine (0.1 mmol/kg). After 6 h organs were removed and the DNA was extracted, hydrolyzed in 0.1 M HCl, and subjected to radiochromatography on Sephasorb-HP. Highest levels of DNA alkylation were found in esophagus (798 mumol 7-methylguanine/mol mol guanine), followed by nasal epithelium (672 mumol) and liver (624 mumol). Trachea, lung, forestomach, and kidney had considerably lower levels of alkylation and in glandular stomach, spleen, and duodenum, values were close to the limit of detection. Specific target cell populations were identified autoradiographically and by immunohistochemistry using a rabbit antiserum to O6-methyldeoxyguanosine. In the esophagus, NMAA was selectively metabolized by the basal cells of the mucosa. In the respiratory tract, O6-methyldeoxyguanosine was almost exclusively present in the tracheal and bronchiolar epithelia. In the nasal cavity, labeled nuclei were found in both the olfactory and the respiratory epithelium and in the serous glands. Our studies indicate that NMAA and related asymmetrical nitrosamines are, in addition to liver, preferentially metabolized in tissues derived from the ventral entoderm, including the upper respiratory and gastrointestinal tract.     

Endogenous nitrosation in the oral cavity of chewers while chewing betel quid with or without tobacco

In order to evaluate endogenous nitrosation in the oral cavity of chewers of betel quid with tobacco (BQT) or without tobacco (BQ), saliva samples were collected from healthy male volunteers after chewing sequentially (i) unmodified BQT or BQ, (ii) BQT or BQ to which proline has been added, and (iii) BQT or BQ to which proline and ascorbic acid had been added. Samples were collected over 20 min and analysed for N-nitrosoproline (NPRO), tobacco-specific nitrosamines (TSNA) and areca nut-specific nitrosamines using gas chromatography-thermal energy analysis, arecoline and nicotine using gas chromatography-nitrogen phosphorus-specific detector, and for nitrite and thiocyanate. When results were expressed as a ratio of NPRO (ng/ml) to nicotine (micrograms/ml), all BQT chewers had increased NPRO contents after chewing BQT with proline. For BQ chewers, when the results were expressed as a ratio of NPRO (ng/ml) to arecoline (micrograms/ml), a similar increase in NPRO content was observed. However, the presence of ascorbic acid inhibited the increased nitrosation in only four out of ten BQT chewers and in five out of ten BQ chewers; in the rest of the samples, its presence enhanced the levels of NPRO. N'-Nitrosoanatabine (NAT) and N-nitrosoguvacoline (NGCO) levels decreased significantly in saliva of chewers of BQT in the presence of ascorbic acid, suggesting inhibition of their formation. In-vitro nitrosation of BQT/BQ with proline and proline plus ascorbic acid showed a similar pattern of nitrosation at salivary pH. The study confirmed previous results that certain nitrosamines are formed during the chewing of BQT/BQ.     

Comparative tumorigenicity of N-nitroso-2-hydroxymorpholine, N-nitrosodiethanolamine and N-nitrosomorpholine in A/J mice and F344 rats

N-Nitroso-2-hydroxymorpholine (NHMOR), a genotoxic metaboliteof the environmental carcinogens N-nitrosomor-pholine (NMOR)and N-nitrosodiethanolaraine (NDELA), was assayed for tumorigenidtyin A/J mice and F344 rats. Groups of female mice were givenNHMOR, NMOR or NDELA in the drinking water over a 10-week period;total doses were 53–55 µmol/mouse. The experimentwas terminated after 30 weeks. Whereas NMOR was a potent tumorigen,inducing 20.3 lung tumors/mouse, NHMOR and NDELA were only weaklytumorigenic, giving 1.2 and 1.4 lung tumors/mouse respectively.Groups of female F344 rats were also given these three nitrosaminesin drinking water for 50 weeks, as follows: NHMOR, total dose0.6 mmol/rat; NHMOR, 1.2 mmol; NMOR, 1.1 mmol and NDELA, 5.6mmol. The experiment was terminated after 120 weeks. NMOR wasa potent carcinogen, inducing liver tumors in 100% of the rats.NDELA gave hepatocelhilar tumors in 70% of the rats. NHMOR wasinactive even at the higher dose. The results of this studydo not support the hypothesis that NHMOR is a proximate carcinogenof NDELA or NMOR.     

Effects of chronic ethanol consumption on the metabolism and carcinogenicity of N'-nitrosonornicotine in F344 rats

The effects of chronic ethanol consumption on the carcinogenicity and metabolism of N'-nitrosonornicotine (NNN) in male F344 rats have been investigated. Groups of 26 to 30 rats were maintained on either a control liquid diet (Groups 1, 3, and 5) or an ethanol-containing liquid diet (Groups 2, 4, and 6) for 4 weeks prior to and during treatment with NNN. The carcinogen was injected s.c. (10 mg/kg, Groups 3 and 4) three times weekly or added to the liquid diet (17.5 mg/liter, Groups 5 and 6). The total dose was 1 mmol of NNN per rat. Control rats (Groups 1 and 2) received s.c. injections of 0.9% NaCl solution. The nasal mucosa was the main target tissue of NNN in Groups 3 and 4, but both the nasal mucosa and esophagus were major target tissues in Groups 5 and 6. In rats treated s.c. with NNN (Groups 3 and 4), ethanol consumption had no effect on the distribution and incidence of nasal cavity tumors. In rats treated with NNN added to the control liquid diet or to the ethanol-containing liquid diet, the number of tumors of the nasal cavity was 18 in Group 5 and 26 in Group 6 (p less than 0.05). In contrast, the number of rats with esophageal tumors was 25 in Group 5 and 20 in Group 6 (p less than 0.05). The effects of ethanol on the enzyme system which activates NNN were studied in rats which had been maintained on an ethanol-containing liquid diet for 4 weeks. Explants of nasal mucosae, lingual mucosae, esophagi , and livers were cultured in vitro with NNN. Nasal mucosae of ethanol-consuming rats had a 1.5-fold higher (p less than 0.05) alpha-carbon-hydroxylating activity than did those of control rats. Activating enzymes in the lingual mucosae, esophagi , and livers were not induced by ethanol. The results show that the increased susceptibility of the rat nasal mucosa to the carcinogenic effects of NNN added to an ethanol-containing diet could be due in part to an induction of activating enzymes by ethanol. However, since chronic ethanol consumption had no apparent effect on the incidence of nasal cavity tumors in rats treated by s.c. injection of NNN, factors other than enzyme induction are important in determining the effects of ethanol on NNN carcinogenicity.     

Chromosomal alterations affecting the 1cen-1q12 region in buccal mucosal cells of betel quid chewers detected using multicolor fluorescence in situ hybridization

Epidemiological studies have shown that a high incidence of oral cancers is associated with chewing betel quid. Since chromosomal aberrations are involved in many types of cancers, we investigated whether increased frequencies of chromosomal alterations could be detected in the oral mucosa cells of betel quid chewers as compared to non-chewers. Due to the difficulty in culturing these epithelial cells, we used multicolor FISH with adjacent DNA probes to detect hyperdiploidy and breakage/exchanges affecting the 1cen-q12 region in interphase cells. Buccal mucosa cells from 19 male betel quid chewers and 23 non-chewers were hybridized and 1000 cells per donor were evaluated. A highly significant increase in the frequency of breakage affecting 1cen-1q12 region was observed in the mucosa cells of the chewers as compared to the non-chewers. A good correlation was also seen between breakage and duration of chewing. A modest increase in hyperdiploidy for chromosome 1 was also observed among chewers who had used betel quid for many years. These results indicate that this FISH approach can be useful for human biomonitoring, particularly for detecting alterations in non-dividing cells.      

Micronuclei in exfoliated human cells as a tool for studies in cancer risk and cancer intervention

The use of the micronucleus test on exfoliated cells as an approach to identify genotoxic damage in human tissues which are targets for organ-specific carcinogens and from which carcinomas will develop, is described. Chromosomal damage by carcinogens to dividing basal cells of the epithelium results in the production of micronuclei in the daughter cells which migrate up through the epithelium and are exfoliated. Exfoliated cells can be readily obtained from several tissues, including the oral buccal mucosa (scrapings of oral cells), bronchi (sputum), urinary bladder and ureter (centrifugation of urine), cervix (smears) and esophagus (imprints from biopsies). The micronucleus test on exfoliated cells has been successfully used to: (1) recognize population groups at an elevated risk for cancer of the oral cavity or urinary bladder; (2) estimate synergistic or additive effects of carcinogen exposure (cigarette smokers plus drinkers of alcoholic beverages); (3) pinpoint the site within an organ from which most carcinomas will develop (oral cancers among 'inverted' smokers in the Philippines). The possibility that this assay may also serve as a rapid monitor for chemopreventive agents is suggested by a preliminary trial on the effect of vitamin A/beta--carotene dietary supplementation among 33 betel quid chewers in the Philippines. These individuals received sealed capsules of retinol (100,000 IU/week) and beta-carotene (300,000 IU/week) for a 3-month period. At the end of this time, the frequencies of micronucleated buccal mucosa cells were reduced from an average of 4.2% to 1.4%. No changes were observed in micronucleus frequencies among 11 betel quid chewers not receiving vitamin pills. Non- chewers of betel quid in this population had a micronucleus frequency of 0.5%.     

Chemical studies on tobacco smoke. XXXIII. N' -nitrosonornicotine in tobacco: analysis of possible contributing factors and biologic implications.

A chemical analytic method to determine N'-nitrosonornicotine (NNN) and N' -nitrosoanabasine (NAB) in tobacco was developed. NNN was found in the unburned tobacco of commercial products at concentrations betweeen 0.3 and 88.6 mug/g. The highest levels were observed in highly fermented snuff (29.1 mug/g) and fine-cut chewing tobacco (88.6 mug/g). NAB was not detected (smaller than 0.5 ng/g) in any tobacco examined. Two new tobacco components, N' -carbomethoxynornicotine and N' -carbomethoxyanabasine,were found. Possible origins of NNN in tobacco were discussed, especially in relation to concentrations of nitrite, nitate, and alkaloids, and in relation to pH and curing. Biologic implications, including the possible function of NNN (the first organic carcinogen isolated from unburned tobacco) as a causative factor in cancer of the oral cavity in tobacco chewers and betel quid chewers, were also discussed.     

Betel quid without tobacco as a risk factor for oral precancers

The IARC monographs recently classified chewing betel quid without tobacco as a human carcinogen. Several studies in Taiwan have reported that betel quid without tobacco may increase the risk of oral precancers such as oral leukoplakia and oral submucous fibrosis. However in India, since most betel quid chewers prefer to add tobacco to the quid, the independent effect of betel quid on the risk of oral precancers is difficult to assess and has not yet been fully explored. We conducted a large case-control study in Kerala, India, including 927 oral leukoplakia cases, 170 oral submucous fibrosis cases, 100 erythroplakia cases, 115 multiple oral precancer cases and 47,773 controls. The focus of this reanalysis is on the minority of individuals who chewed betel quid without tobacco. Among nonsmokers and nondrinkers, chewing betel quid without tobacco conferred ORs of 22.2 (95%CI = 11.3, 43.7) for oral leukoplakia, 56.2 (95%CI = 21.8, 144.8) for oral submucous fibrosis, 29.0 (95%CI = 5.63, 149.5) for erythroplakia and 28.3 (95%CI = 6.88, 116.7) for multiple oral precancers, after adjustment for age, sex, education and BMI. Dose-response relationships were observed for both the frequency and duration of betel quid chewing without tobacco on the risk of oral precancers. In conclusion, our study supports the hypothesis that chewing betel quid without tobacco elevates the risks of various oral precancers.     

Betel quid not containing tobacco and oral cancer: a report on a case-control study in Papua New Guinea and a meta-analysis of current evidence

Smoking and betel quid chewing are associated with increased risk of oral cancer but few studies have reported on associations in populations where betel quid does not contain tobacco. We conducted a case-control study in Papua New Guinea and a systematic review. Our case-control study recruited 143 cases with oral cancer and 477 controls. We collected information on smoking and betel quid chewing. Current smoking was associated with an increased risk of oral cancer with an adjusted odds ratio (OR) for daily smokers of 2.63 (95% confidence intervals (95% CI) 1.32, 5.22) and amongst heaviest smokers of 4.63 (95% CI 2.07, 10.36) compared to never-smokers. Betel chewing was associated with increased risk of oral cancer with an adjusted OR for current chewers of 2.03 (95% CI 1.01, 4.09) and in the heaviest chewers of 2.47 (95% CI 1.13, 5.40) compared to nonchewers. The OR in those who both smoked tobacco and chewed betel quid was 4.85 (95% 1.10, 22.25), relative to those who neither smoked nor chewed. The systematic review identified 10 previous studies that examined risk of oral cancer associated with betel quid chewing that controlled for smoking in populations where betel quid did not contain tobacco. In studies that reported results for non-smokers the combined OR was 2.14 (95% CI 1.06, 4.32) in betel quid chewers and in studies that adjusted for smoking the combined OR was 3.50 (95% CI 2.16, 5.65) in betel quid chewers. Preventive efforts should discourage betel quid chewing as well as smoking.