Surgical Oncology (2009) 18, 51e56

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REVIEW

Helicobacter species are associated with possibleincrease in risk of hepatobiliary tract cancers

Manoj Pandey a,*, Mridula Shukla b

a Department of Surgical Oncology, Institute of Medical Sciences, Banaras Hindu University, Varanasi 221 005, Indiab Department of Pathology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, 221 005 India

Accepted 2 July 2008

KEYWORDSGallbladder;Bile duct cancer;Helicobacter;Carcinogenesis;Meta analysis

* Corresponding author. Tel./fax: þE-mail address: manojpandey@vsn

0960-7404/$ - see front matter ª 200doi:10.1016/j.suronc.2008.07.002

Abstract

Background: Attempts at early identification of hepatobiliary cancers have failed due to non-availability of a sensitive test. Prevention offers the best chance to reduce the morbidity andmortality from these. Identification of an etiological agent and especially if the potentiallyidentified cause can be eradicated like Helicobacter sp. infection, will not only reduceincidence but also the mortality.Methods: This article reviews 15 studies on Helicobacter species in hepatobiliary cancers iden-tified on pubmed, scopus and google scholar search. Of these, Five were single group and10 were case control. These 10 case control studies were included in the meta analysis, whichwas carried out using odds ratio and both a fixed and random effect model, 95% confidenceintervals for odds ratio was calculated. Chi square test for heterogeneity was employed.The overall effect was calculated using Z test.Results: The cumulative sample size of cases was 205, of which 115 were positive (56%) forHelicobacter, while among 263 controls 53 (20%) were found to be positive for Helicobacterinfection. The positivity rate in case control studies was higher than that observed in singlegroup studies. The cumulative odds ratio for the study sample was 8.72 (95% CI 4.78e15.91)(Z Z 7.07; p < 0.00001).Conclusions: There is enough evidence to suggest a possible role of Helicobacter species inhepatobiliary tract cancers. However, the results from different regions of the world differ.Studies also differ on method of Helicobacter detection, subsite of cancer with in the hepato-biliary tract and choice of controls thus introducing heterogeneity. Further case control studieswith larger sample size are required to settle the question.ª 2008 Elsevier Ltd. All rights reserved.

91 542 236 6014.l.com (M. Pandey).

8 Elsevier Ltd. All rights reserved.

52 M. Pandey, M. Shukla

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Conflict of interest statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Introduction

The hepatobiliary tract cancers are one of the commonestcancers among females in Eastern Uttar Pradesh andWestern Bihar regions of India [1,2] and the third common-est cancer of the gastrointestinal tract in developed coun-tries. The exact incidence is not known in Eastern UttarPradesh due to absence of any cancer registry in thispart. However, hospital data suggest that up to 16% of allcancers are of hepatobiliary origin making it the secondbiggest group after head and neck cancer [2]. The exactetiology of this cancer is not known. Several factors havebeen proposed. Of these cholelithiasis is commonly impli-cated [3,4]. Bacterial infections like typhoid too has beeninvestigated [5,6], however, there is no concludingevidence of its definite role in carcinogenesis. Severalauthors have proposed a multifactorial model where morethan one factor act synergistically to produce cancer.Several studies have tried to examine the role of Helico-bacter sp. in hepatobiliary carcinogenesis [7e21]. Howeverdue to deficiency of study design like use of differentmethods of detection, absence of control group, smallersample sizes, etc., none of the studies could answer thequestion [7e21]. Hepatobiliary tract cancers are highlyaggressive and once diagnosed they are rapidly fatal andhence, prevention is the best alternative. If a causativeassociation could be demonstrated with Helicobacter thenit will be possible to reduce the incidence of these cancersin this subgroup by eradicating the Helicobacter. This arti-cles review the published literature with critical assess-ment and meta analysis of the role of Helicobacterspecies in hepatobiliary tract diseases.

Methods

A detailed pubmed (Medline), scopus and google scholarsearch was made using keywords ‘hepatobiliary’, ‘cholan-giocarcinoma’, ‘hepatocellular carcinoma’ ‘Klatskin tumor’‘gallbladder’ and ‘cancer’, or ‘carcinoma’, or ‘neoplasia’,or ‘tumor’, and Helicobacter. The search was then limitedto humans and publication year 1990eMay 2008. The arti-cles were carefully read and were classified into observa-tional single group or case control type. All articles onbenign diseases or where it was not clear as to what diseasewas evaluated were excluded. The data on the method ofdetection, number of positive cases for Helicobacter insubjects and controls and the type of organism identifiedwere extracted and entered in the database prepared for

the purpose. All samples analyzed in the study were takenirrespective of methods of detection used. If a study usedthree methods of detection, the sample of the threemethods was summed to get the total number and numberof positive cases, this led to an increase in the sample sizeas some of the patients were counted twice, once for eachmethod. Meta analysis was carried out for the above datafrom the case control studies despite their heterogeneitywith the goal that if an association is observed this willhelp in designing further studies and will also help us tounderstand what kind of studies are exactly required.

Meta analysis was performed with Review Manager 4.2.2software. The analysis was carried out by calculating oddsratio and a fixed as well as a random effect model, 95%confidence intervals for odds ratio was calculated. Chisquare test for heterogeneity was employed. The overalleffect was calculated using Z test, and inconsistency amongstudies with I2.

Results

The search identified a total of 15 studies on Helicobacterspecies in hepatobiliary tract cancers. Of these therewere five single group observational studies [7e11] and 10case control studies [12e21], which form the basis forthis meta analysis. Of the 10 case control studies threewere on gallbladder cancer, three on hepatobiliary tractcancers, one on primary liver cancer, one included bothcholangio and hepatocellular carcinoma [11e21] whileother two also included benign diseases beside cancerpatients [16,17].

In the five single group studies a total of 328 subjectswere evaluated of which only 27 (8.2%) showed positivityfor Helicobacter infection (Table 1). In the 10 case controlstudies the cumulative sample size of cases was 205 ofwhich 115 were positive (56%), while of 263 controls inthe same studies only 53 (20%) were positive for Helico-bacter infection. The positivity rate in case control studieswas higher than that observed in single group studies. All ofthe studies used PCR for 16s RNA as a method of identifica-tion of Helicobacter while two used culture besides PCR.Both bile and tissues were used for analysis. A number ofHelicobacter species were identified of which Helicobacterbilis was by far the commonest, Helicobacter pylori andHelicobacter pullorum beside unclassified species werealso identified (Table 2).

The cumulative odds ratio for the sample was 8.72 (95%CI 4.78e15.91) (Z Z 7.07; p < 0.00001) using fix effect

Table 1 Characteristics of observational studies on Helicobacter sp. in hepatobiliary cancers.

Referenceand year

Method ofdetection

Specimen Disease Helicobacterpositivity

Organismidentified

Lin et al. 1995 [7] PCR (UreA) Bile Mix. Including malignancy 3/7 H. pyloriRoe et al. 1999 [9] PCR (UreA) Bile Cholangio carcinoma 10/32 Helicobacter sp

(16s rRNA) Pancreatic cancerHepatolithiasis

Pradhan andDali 2004 [8]

Histology Gallbladder Mix 6/7 malignant76/93 benign

Helicobacterhepaticus

Fallone et al.2003 [10]

Helicobactergenus-specific primers

Bile Cholelithiasis 3/125 H. pylori

Pancreatico-biliarymalignanciesSclerosing cholengitis

Vivekanandanet al. 2008 [11]

PCR Helicobactergenus-specific primers,H. pylori primers

Tumornon-tumorsamples

HCC and otherbenign diseases

0/22 HCC0/10 CC5/17 other

Helicobacter sp.and H pylori

Helicobacter species are associated with possible hepatobiliary tract cancers 53

model (Fig. 1), and 8.42 (95% CI 3.70e19.20) (Z Z 5.07;p < 0.00001) using random effect model (Fig. 2), favoringrole of Helicobacter in hepatobiliary malignancies.

Discussion

The genus of Helicobacter has expanded to includea number of species [22]. The most studied among theseis Helicobacter pylori (H. pylori), that colonizes thestomach and has been found to be associated with gastritis[23], peptic ulcer disease [24], mucosa associated lymphoidtissue (MALT) lymphoma [25] and stomach cancer [26].Some other species like H. hepaticus and H. bilis havebeen shown to infect the liver and the presence of themhas been associated with hepatitis and hepatobiliaryneoplasms [8,22,27,28].

Infection by Helicobacter species is the first bacterialinfection recognized as carcinogenic in humans [29]. Thecomplete genomic sequence of H. pylori and H. hepaticusis now known. With the identification of H. pylori the para-digm for the management of peptic ulcer, chronic gastritis,MALT lymphoma and gastric adenocarcinoma has under-gone paradigm shift [30,31].

Cancer of the liver and biliary tract, though relativelyrare in the west; are common in some countries like Japan,Chile, India and Poland [32]. In India there are pockets ofhigh incidence, in north India and it is very low in South India[33]. The etiology and pathogenesis, in the background ofdiverse geographical occurrence is unclear. This suggestsa presence of multifactorial etiology of occurrence [3e6,34]. A close examination indicates that the majority ofthese studies are mistaking ‘‘association’’ as causativefactor. As it is, no causative factor has been identified so far.

The concept of investigating bacterial association withmalignancy is not new. In the context of gallbladder cancer,typhoid carrier state has been found to be associated withincreased risk of gallbladder cancer [5,6]. Similarly there isstrong association of Helicobacter sp. with diseases of thehepatobiliary tract cancer. The Helicobacter sp has beenidentified in human bile [15,35] and they have been

reported to survive in bile juice and has been identified inbile juice of patients with cholelithiasis, primary sclerosingcholangitis and primary biliary cirrhosis [7,12,17,36,37].A PCR study by Fukuda et al. [15] in biliary bile and tissuesuggested a role of Helicobacter sp. in biliary tract carcino-genesis. Another recent PCR study too suggested a role forH. bilis in bile duct and gallbladder cancer [17]. However,studies which tried to culture the organism in bile or tissuehave been unsuccessful [7,19], creating controversy ofuncertainty over the role of Helicobacter sp. in biliary tractdisease. The results of meta analysis however favors a roleof Helicobacter in malignancies of the hepatobiliary tract,though heterogeneity in these studies is too high. Varioussamples have been analyzed like bile or tissue and differingmethods of detection have been used.

The exact mechanism by which Helicobacter causes hep-atobiliary tract carcinogenesis is not clear. CagA, a viru-lence factor from H. pylori is assumed to play a role ingastrointestinal diseases by disturbing signal transductionin host cells after translocation [38]. It is also proposedthat Helicobacter may also promote the risk of stone forma-tion by acting as a foreign body nidus around which thestone may develop or it may produce hydrolyzing enzymesor nucleating proteins like immunoglobulins. CagA proteinof Helicobacter has been found to have a homology withaminopeptidase and hence can increase the gallstoneformation. Beside these mechanisms Helicobacter sp.have also been proposed to increase the lithogenicity byproduction of soluble antigens that may bind to and inhibitkey hepatobiliary genes like muc [39]. This may lead tomodulation of enterohepatic cycling of conjugated bileacids through genetic regulation of absorption at entero-cyte level or modulation of the transit time through gut[40]. Host response to Helicobacter antigens in form ofcytokines, and other inflammatory mediators are alsoproposed to play a role [40].

Thus there is a maze of mechanisms by which Helico-bacter could be related to hepatobiliary carcinogenesis.Helicobacter may produce epithelial injury followed bychronic inflammatory states like stones that can cause

Table 2 Characteristics of case control studies on Helicobacter sp in hepatobiliary malignancies.

Referenceand year

Method ofdetection

Specimen Disease Helicobacterin subjects

Helicobacterin controls

Organismidentified

Fox et al.1998 [11]

PCR(16s rRNA)

Bile Chr. Cholecystitis 13/23 bile 0/2 Helicobacter species(H. bilis, Flexispirarappini, H. pullorum)

GB Ca GB 9/23 tissue

Avenaud et al.2000 [12]

PCR(16s rRNA)

Primary livercancer

8/8 1/8 H. pylori, HepaticHelicobacter sp.

Murata et al.2004 [13]

PCR(16s rRNA)

GB Ca GB 3/11 GBC 2/16cholelithiasis

H bilisBile duct ca 1/3 BDCPancreatic Ca 0/4Cholelithiasis

Fukuda et al.2002 [14]

PCR Bileand tissue

Hepatobiliarycancer

10/19 3/19 Helicobacter sp.

Kobayashi et al.2005 [15]

PCRculture

Bile Mix. Incl cancer 16/30 benign 2/21 Helicobacter sp.5/6 Ca

Matsukura et al.2002 [16]

PCR16s rRNA

Bile Biliary tractcancer

24/29 malignant 4/14 H. bilis

Gallstones 18/42 stoneBohr et al.

2007 [18]Culture gallbladder

tissuegallstones,gallbladdercancer andnormal

0/20 cancer 0/22 control H. pylori16s rRNA 1/57 stones

Nilsson et al.2000 [19]

PCR 16srRNA

tissue HCC and CC CC 10/12 0/20 H. pylori andHelicobacter sp.HCC 10/14

Huang et al.2004 [20]

PCR 16srRNA

Livertissue

Primary livercarcinomaand control

8/20 primaryliver

0/10 Helicobacter sp.

Bulajic et al.2002 [21]

PCR 16srDNA

Bile andtissue

Malignantbiliary tumors

12/15 biliarytumors

37/63gallstones

H. pylori

3/11 normal

54 M. Pandey, M. Shukla

proliferation of biliary epithelial cells [39]. This prolifera-tion may lead to dysplasia or metaplasia and may laterprogress to cancer similar to the mechanism of occurrenceof hepatoma in cirrhosis or carcinoma of the esophagus inBarrett’s esophagus. The Helicobacter has also been shownto increase the cell kinetics and thus may produce similarresults [40]. Fox et al. [11] also proposed a similar mecha-nism of epithelial injury occurring through cytotoxinproduction.

Review: Helicobacter in hepatobiliary diseasesComparison: 01 Helicobacter in biliary tract (over all effect all studies) Outcome: 03 Helicobacter in hepatobiliary cancers

Study Cases Controlor sub-category n/N n/N

Fox et al 22/46 0/2

Avenaud et al 8/8 1/8

Nillson et al 22/30 0/20

Bulajic et al 12/15 40/74

Fukuda et al 10/19 3/19

Matsukura et al 24/29 4/14

Huang et al 8/20 0/16

Murata 2004 4/18 2/16

Kobayashi et al 5/6 2/21

Bohr et al 0/20 1/79

Total (95% CI) 211 269

Total events: 115 (Cases), 53 (Control)Test for heterogeneity: Chi² = 12.94, df = 9 (P = 0.17), I² = 30.4%Test for overall effect: Z = 7.07 (P < 0.00001)

0.1 0.2 Does not fav

Figure 1 Results of meta analysis of 10 case control studies

All the case control and observational studies haveshown higher percentage of Helicobacter in samples frommalignant neoplasms. However the evidence of a casualrelationship produced by this meta analysis is not robustenough to claim a role of Helicobacter without doubt dueto high heterogeneity of studies. An experimental evidenceto confirm the cancer producing effect of Helicobacterinfection will bring the uncertain relation of Helicobacterand biliary tract diseases to conclusion.

OR (fixed) Weight OR (fixed) 95% CI % 95% CI Year

5.75 4.59 [0.21, 100.90] 1998 0.98 85.00 [2.99, 2417.50] 2000 1.92 108.53 [5.89, 2000.78] 200031.66 3.40 [0.89, 13.05] 200216.68 5.93 [1.29, 27.28] 200210.92 12.00 [2.66, 54.19] 2002 3.86 22.44 [1.18, 426.74] 200419.34 2.00 [0.31, 12.75] 2004 1.74 47.50 [3.55, 636.17] 2005 7.15 1.28 [0.05, 32.50] 2007

100.00 8.72 [4.78, 15.91]

0.5 1 2 5 10our Favours Helicobacter

on hepatobiliary tract malignancies using fix effect model.

Review Helicobacter in hepatobiliary diseasComparison 01 Helicobacter in biliary tract (over all effect all s tudies) Outcome 03 Helicobacter in hepatobiliary cancers

Study Cases Control Weight OR (random)or sub-category n/N

OR (random)n/N 95% CI % 95%CI Year

Fox et al 22/46 0/2 5.91 4.59 [0.21, 100.90] 1998

Avenaud et al 8/8 1/8 5.16 85.00 [2.99, 2417.50] 2000

Nillson et al 22/30 0/20 6.51 108.53 [5.89, 2000.78] 2000

Bulajic et al 12/15 40/74 18.10 3.40 [0.89, 13.05] 2002

Fukuda et al 10/19 3/19 15.89 5.93 [1.29, 27.28] 2002

Matsukura et al 24/29 4/14 16.11 12.00 [2.66, 54.19] 2002

Huang et al 8/20 0/16 6.39 22.44 [1.18, 426.74] 2004

Murata 2004 4/18 2/16 12.64 2.00 [0.31, 12.75] 2004

Kobayashi et al 5/6 2/21 7.83 47.50 [3.55, 636.17] 2005

Bohr et al 0/20 1/79 5.46 1.28 [0.05, 32.50] 2007

Total (95% CI) 211 269 100.00 8.42 [3.70, 19.20]

Total events: 115 (Cases), 53 (ControTest for heterogeneity: Chi² = 12.94, df = 9 (P = 0.17), I² = 30.4%Test for overall effect: Z = 5.07 (P < 0.00001

0.1 0.2 0.5 1 2 5 10Does not favour Favours Helicobacte

Figure 2 Results of meta analysis of 10 case control studies on hepatobiliary tract cancer using random effect model.

Helicobacter species are associated with possible hepatobiliary tract cancers 55

Conflict of interest statement

The authors declare that there are no conflicts of interest.MP is editor-in-Chief of World Journal of Surgical Oncology,sectional editor of Indian Journal of Surgery an officialpublication of Association of Surgeons of India and iseditorial secretary of IASO News letter an official publica-tion of Indian Association of Surgical Oncology.

References

[1] Shukla VK, Khandelwal C, Roy S, Vaidya MP. Primary carcinomaof the gallbladder. A review of 16 years period at UniversityHospital. J Surg Oncol 1985;28:32e5.

[2] Pandey M, Pathak AK, Singh S, Gautam A, Shukla VK. Carci-noma of the gallbladder: a retrospective review of 99 cases.Dig Dis Sci 2001;46:1145e51.

[3] Piehler JM, Crichlow RW. Primary carcinoma of the gallbladder.A collective review. Surg Gynaecol Obstet 1978;147:929e42.

[4] Diehl AK. Gall stone size and the risk of gallbladder cancer.JAMA 1983;250:2323e6.

[5] Shukla VK, Singh H, Pandey M, Upadhyaya SK, Nath G. Carci-noma of the gallbladder is it sequel of typhoid? Dig Dis Sci2000;45:900e3.

[6] Singh H, Pandey M, Shukla VK. Salmonella typhi carrier statechronic bacterial infection and gallbladder carcinogenesis.Eur J Cancer Prev 1996;5:144.

[7] Lin TT, Yeh CT, Wu CS, Liaw YF. Detection and partialsequence analysis of Helicobacter pylori DNA in bile samples.Dig Dis Sci 1995;40:2214e9.

[8] Pradhan SB, Dali S. Relation between gallbladder neoplasmand Helicobacter hepaticus infection. Kathmandu Univ MedJ 2004;2:331e5.

[9] Roe IH,KimJT, LeeHS, LeeJH.DetectionofHelicobacter DNA inbile from bile duct diseases. J Korean Med Sci 1999;14:182e6.

[10] Fallone CA, Tran S, Semret M, Discepola F, Behr M, Barkun AN.Helicobacter DNA in bile: correlation with hepato-biliarydiseases. Aliment Pharmacol Ther 2003;17:453e8.

[11] Vivekanandan P, Torbenson M. Low frequency of HelicobacterDNA in benign and malignant liver tissue from, Baltimore,United states. Hum Pathol 2008;39:213e6.

[12] Fox JG, Floyd ED, Shen Z, Feng Y, Taylor NS, Paster BJ,et al. Hepatic Helicobacter sp. identified in bile and gall-bladder tissues from Chileans with chronic cholecystitis.Gastroenterology 1998;114:755e63.

[13] Avenaud P, Marais A, Monteiro L, Le Bail B, Bioulac Sage P,et al. Detection of Helicobacter species in the liver of patientswith and without primary liver carcinoma. Cancer 2000;89:1431e9.

[14] Murata H, Tsuji S, Tsujii M, Fu HY, Tanimura H, Tsujimoto M,et al. Helicobacter bilis infection in biliary tract cancer.Aliment Pharmacol Ther 2004;20(Suppl. 1):90e4.

[15] Fukuda K, Kuroki T, Tajima Y, Tsuneoka N, Kitajima T,Matsuzaki S, et al. Comparative analysis of HelicobacterDNAs and biliary pathology in patients with and without hep-atobiliary cancers. Carcinogenesis 2002;23:1927e31.

[16] Kobayashi T, Harada K, Miwa K, Nakanuma Y. Helicobactergenus DNA fragments are commonly detectable in bile frompatients with extra hepatic biliary diseases and associatedwith their pathogenesis. Dig Dis Sci 2005;50:862e7.

[17] Matsukura N, Yokomuro S, Yamada S, Tajiri T, Sundo T,Hadama T, et al. Association between Helicobacter bilis inbile and biliary treat malignancies: H. bilis in bile from Japa-nese and Thai patients with benign and malignant diseases inthe biliary tract. Jpn J Cancer Res 2002;93:842e7.

[18] Bohr URM, Kuester D, Meyer F, Wex T, Stillert M, Csepregi A,et al. Low prevalence of Helicobacteraceae in gall-stonedisease and gall-bladder carcinoma in the German population.Clin Microbiol Infect 2007;13:525e31.

[19] Nilsson HO, Mulchandani R, Trenberg KG, Stenram U,Wadstrom T. Helicobacter species identified in liver frompatients with cholangiocarcinoma and hepatocellular carci-noma. Gastroentrology 2001;120:323e4.

[20] Huang Y,Fan XG,WangZM,Zhou JH,Tian XF, LiN. Identification ofHelicobacter species in human liver samples from patients withprimary hepatocellular carcinoma. J Clin Pathol 2004;57:1273e7.

[21] Bulajic M, Maisonneuve P, Schneider-Brachert W, Muller P,ReischlU, StimecB, et al.Helicobacterpylori and the risk of benignand malignant biliary tract disease. Cancer 2002;95:1946e53.

[22] Franklin CL, Beckwith CS, Livingston RS, Riley LK, Gibson SV,Besch-Williford CL, et al. Isolation of a novel Helicobacterspecies, Helicobacter cholecystus sp. nov., from gallbladder ofSyrian Hamsters with cholangiofibrosis and centrilobular pancre-atitis. J Clin Microbiol 1996;34:2952e8.

[23] Marshall BJ. Campylobacter pylori: its link to gastritis andpeptic ulcer disease. Rev Infect Dis 1990;157:465e71.

[24] Marshall BJ, Warren JR. Unidentified curved bacilli in thestomach of patients with gastritis and peptic ulceration.Lancet 1984;i:1311e4.

[25] Wotherspoon AC, Ortiz-Hidalgo C, Falzon MR, Isaacson PG.Helicobacter pylori associated gastritis and primary B-cellgastric lymphoma. Lancet 1991;338:1175e6.

56 M. Pandey, M. Shukla

[26] Parsonnet J, Vandersteen D, Goates J, Sibley RK, Pritikin J,Chang Y. Helicobacter pylori infection in intestinal and diffuse-type gastric adenocarcinomas. J Natl Cancer Inst 1991;83:640e3.

[27] Fox JG, Dewhirst FE, Tully JG, Paster BJ, Yan L, Taylor NS,et al. Helicobacter sp. nov., a microaerophilic bacterium iso-lated from bile, liver and intestinal mucosal scrapings frommice. J Clin Microbiol 1994;32:1238e45.

[28] Avenaud P, Le Bail B, Mayo K, Marais A, Fawaz R, Bioulac-Sage P, et al. Natural history of Helicobacter hepaticus infec-tion in conventional A/J mice, with special reference to liverinvolvement. Infect Immun 2003;71:3667e72.

[29] Schistosomes, liver flukes and Helicobacter pylori. IARCWorking Group on the Evaluation of Carcinogenic Risks toHumans. Lyon, 7–14 June 1994. IARC Monogr Eval CarcinogRisks Hum. 1994;61:1e241.

[30] Mendall MA, Goggin PM, Molineaux N, Levy J, Toosy T,Strachan D, et al. Relation of Helicobacter pylori infectionand coronary artery disease. Br Heart J 1994;71:437e9.

[31] Gasbarrini A, Franclschi F, Tartaglione R, Landolfi R,Pola P, Gasbarrini G. Regression of autoimmune thrombocy-topenia after eradication of Helicobacter pylori. Lancet1998;352:878.

[32] Parkin DM, Whelan SL, Ferlay J, Teppo L, Thomas DB, editors.Cancer incidence in five continents, Vol. VIII. Lyon, IARC: IARCScientific Publications No. 155; 2002.

[33] National Cancer Registry Program. Consolidated report of thepopulation based cancer registries 1990e1996. New Delhi:Indian Council of Medical Research; 2002.

[34] Pandey M. Risk factors for gallbladder cancer: a reappraisal.Eur J Cancer Prev 2003;12:15e24.

[35] Leong RWL, Sung JJY. Helicobacter species and hepatobiliarydiseases. Aliment Pharm Ther 2002;16:1037e45.

[36] Fox JG, Yan LL, Dewhirst FE, Paster BJ, Shames B, Murphy JC,et al. Helicobacter bilis sp. nov. a novel Helicobacter speciesisolated from bile, livers and intestines of aged, inbred mice.J Clin Microbiol 1995;33:445e54.

[37] Higashi H, Tsutsumi R, Muto S, Sugiyama T, Azuma T, Asaka M,et al. SHP-2 tyrosine phosphatase as an intracellular target ofHelicobacter pylori CagA protein. Science 2002;295:683e6.

[38] Murer KJ, Ihrig MM, Rogers AB, Ng V, Bouchard G, Leonard MR,et al. Identification of cholelithogenic enterohepatic Helico-bacter species and their role in murine cholesterol gallstoneformation. Gastroenterology 2005;128:1023e33.

[39] Chen W, Li D, Cannan RJ, Stubbs RS. Common presence ofHelicobacter DNA in the gallbladder of patients with gallstonediseases and controls. Dig Liver Dis 2003;35:237e43.

[40] Myung SI, Kim MH, Shin KN, Kim YS, Kim EO, Kim HJ, et al.Detection of Helicobacter pylori DNA in human biliary treeand its association with hepatolithiasis. Dig Dis Sci 2000;45:1405e12.