Helicobacter pylori: the cancer link.

JOURNAL OF THE ROYAL SOCIETY OF MEDICINE

Helicobacter pylori: the F O'Connor BSc

M Buckley MB MRCPI

Volume 89

December 1 996

link

cancer

C O'Morain MD FRCPI

J R Soc Med 1996;89:674-678

Gastric cancer is the second most commonly diagnosed fatal cancer in the world1 and is characterized by a very poor prognosis in its more advanced stages2. Gastric adenocarcinoma is classified into two distinct histological types intestinal and diffuse3. The intestinal type predominates in high-risk populations, is more common in the elderly and is preceded by a continuum of histological changes in the gastric mucosa including chronic active gastritis, atrophy, intestinal metaplasia and dysplasia4. The diffuse type is less common, occurring more frequently in low-risk populations and mostly in younger people. No well-defined precancerous lesions have been described for this type of gastric cancer4'5. Several factors such as age, family history and diet have been reported to be associated with gastric cancer. In 1994, the International Agency for Cancer Research recognized a cause-and-effect relationship between Helicobacter pylori and gastric adenocarcinoma and classified H. pylori as a group I (definite) carcinogen6. EPIDEMIOLOGY

H. pylori infection causes chronic active gastritis and is present in 90-95% of patients with duodenal ulcer, in 70% of patients with gastric ulcer and in 60% of patients with gastric cancer. The lower prevalence of H. pylori associated with gastric cancer may be attributed to the finding that spontaneous clearance of the bacterium occurs from the stomach with the development of intestinal metaplasia and dysplasia. Geographical studies of gastric cancer incidence and H. pylori prevalence reveal striking parallels between the two. Gastric cancer, like H. pylori infection, has foci of high incidence, usually in populations of low socioeconomic class7'8. In Peru, where gastric cancer rates almost reach epidemic proportions, virtually all adults are infected with H. pylori9. Furthermore, in high-risk cancer regions the infection is acquired in early childhood, in contrast to later infections in regions with low gastric cancer rates10. In their epidemiology, gastric cancer and H. pylori-associated gastritis

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Department of Gastroenterology, Meath/Adelaide Hospitals and Trinity College, Dublin, Ireland Correspondence to: Professor Colm O'Morain, Department of Gastroenterology, Meath Hospital, Heytesbury St, Dublin 8, Ireland

reveal striking similarities. In populations born after the Second World War, a decrease of 30-40% in the incidence of gastritis has been observed, which closely corresponds with a mean decrease of 30% in the incidence of gastric cancer in this population11. Three nested case-controls studies have compared the prevalence of H. pylori-IgG antibodies in stored serum between individuals who subsequently developed gastric cancer and age matched controls12-14. All three demonstrated that the presence of H. pylor antibodies was significantly associated with an increased relative risk of developing gastric cancer (Table 1). For patients diagnosed more than 14 years after blood donation, the odds ratio increased to 8.7 (95% CI 2.7-45) and the seroprevalence of H. pylori was 90%15 (Table 2).

Table 1 Odds ratios for the association between gastric cancer and H. pylonl in prospective studies Location of study

UK

(Ref 12) California

OR

Cases HP+ Controls HP+ Mean (n) (n) (n) follow up (n)

29

20

116

54

6.0

109

92

109

66

14.2

109

103

109

83

13.5

(95%CI) 2.8 (1.0-8.0) 3.6

(1.8-7.3)

(Ref 13) Hawaii

6.0 (2.1-1 7.3)

(Ref 14)

HP+=Helicobacter pylori positive; OR=odds ratio; Cl=confidence intervals

Table 2 Combined analysis of three prospective studies, stratified by time intervals between blood donation and cancer diagnoses Interval Cases

HP+

Controls HP+

(years)

(n)

(n)

(n)

(n)

OR (95%

0-4 5-9 10-14 >14 All

25 46 78 98 247

20 37 70 88 215

58 85 93 98 334

34 46 58 65 203

2.1 2.3 4.4 8.7 3.8

See Table 1 for key to abbreviations

Cl)

(0.6-8.7) (0.9-6.5) (1.8-13.0) (2.7-45.0) (2.3-6.2)


In case-control studies, the prevalence of H. pylori antibodies at the time of clinical diagnosis of gastric cancer has been compared with that in controls. Table 3 summarizes four studies of this typel-'9. Three showed a significant association between the prevalence of H. pylori and gastric cancer16-8. Several large population-based studies have compared the prevalence of H. pylori and the incidence of gastric cancer. The EUROGAST study, involving 17 separate populations from 11 European countries, Japan and the USA, produced an estimated relative risk of 6.08. These studies provide evidence of a strong worldwide association between H. pylori and gastric cancer, clearly implicating the bacterium in the pathogenesis of this disease. HUMAN MODEL FOR GASTRIC CARCINOGENESIS

Intestinal-type gastric carcinoma develops through a sequence of histological events from normal gastric mucosa through superficial gastritis, chronic gastritis, atrophy, intestinal metaplasia and dysplasia and eventually cancer4. Numerous studies have demonstrated the relationship between gastric colonization by H. pylori and chronic active gastritis2 22. Initially, chronic active gastritis is of the superficial non-atrophic type23. With time, the superficial gastritis may become atrophic with deeper extension of the inflammatory cells and loss of antral and fundal glands23. A significant association between the precursor lesion intestinal metaplasia and H. pylori has been demonstrated24. Intestinal metaplasia may be considered as a defensive strategy adopted by the mucosa to eradicate H. pylori, as the bacterium will only colonize gastric epithelium. Intestinal metaplasia can be subdivided on the basis of cell differentiation and mucin secretion into type I, type II and type III25, the last being closely associated with gastric cancer26. We have found that H. pylori is significantly less prevalent in type II and type III intestinal metaplasia than in type 127. Our hypothesis is that, with the progression of intestinal metaplasia from type I to type III, the mucosal architecture becomes less hospitable to H. pylori colonization. We have also shown that, in patients with persistent H. pylori infection, after a follow-up of greater than

December 1996

2 years, only 41% had persistent active gastritis while 54.5% had progressed to chronic atrophic gastritis and 4.5% had developed dysplasia. H. pylori is the starting-point for the development of gastric cancer. Other factors, however, must be present for this cascade of events to result ultimately in this fatal cancer

(Figure 1). CELL KINETICS

Regulation and control of birth, differentiation and loss of cells are key factors in the maintenance of normal growth of tissues29. Cell proliferation is controlled at two levels. The cell cycle is controlled by factors including p34cdc2 and cyclins30 and cell growth is controlled by growth factors31. Increased cell proliferation is a common feature in the pathogenesis of many human cancers and may play a role in carcinogenesis by converting DNA adducts to mutation. In a recent study32, the epithelial cell proliferation of gastric antral mucosa was determined, by means of the bromodeoxyuridine immunohistochemical technique, in patients with normal antral mucosa, chemically induced gastritis or H. pylori-associated gastritis. The patients with H. pylori-associated gastritis had a higher cell turnover than controls (patients with normal mucosa or chemically induced gastritis) but cell proliferation became normal after eradication of H. pylori33. In addition increased epithelial cell proliferation was detected in H. pylori-associated atrophic gastritis, intestinal metaplasia, dysplasia and gastric cancer34. These effects of H. pylori on the cell kinetics of the

H. pylori infection Weeks-months

I

Chronic superficial

gastritis Increased cell

proliferation

Chronic atrophic gastritis

Table 3 Odds ratios for an association betwen gastric cancer and H.

pylon in four case-control studies

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Years-decades

Nutritional factors Genetic factors

{

Intestinal metaplasia Location of study

Cases (n)

HP+

(n)

Controls HP+ (n) (n)

I Spontaneous eradication

OR

of infection

(95%CI)

Dysplasia

USA16 Finland17

Sweden18

Netherlands'9

69 54 112 116

36 38 90 89

252 84 103 116

96 43 63 92

2.8 2.3 2.6 0.9

(1.3-5.6) (1.0-5.0) (1.4-5.0) (0.5-1.7)

Mf

Intestinal-type gastric cancer

Figure 1 Sequence of histological changes leading from H. pylori See Table 1 for key to abbreviations

infection to intestinal-type gastric cancer

675


gastric epithelium provide further evidence of an association between the bacterium and gastric cancer. Several studies have identified abnormalities of tumour suppressor genes, oncogenes and growth factors in the pathogenesis of gastric carcinoma, but as yet these molecular alterations have not been directly attributed to H. pylori infection. It must be stated that these genetic abnormalities are found in the latter stages of gastric cancer development. They may, however, be the end-result of previous H. pylori infection. GASTRIC JUICE MUTAGENICITY

Epidemiological evidence suggests a strong association between high ascorbic acid intake and low incidence of gastric cancer. The protective effect of ascorbic acid may be due to its ability to inactivate reactive oxygen species as well as its nitrite-scavenging effects. Patients with peptic ulcer disease, gastritis, pernicious anaemia and gastric cancer have lower concentrations of ascorbic acid in the gastric juice than do controls3536. Ascorbic acid is secreted by the stomach across the gastric mucosa into the gastric juice against a concentration gradient37. Banerjee et al.38 examined the effect of H. pylori on the secretion of ascorbic acid into the gastric juice by measuring fasting plasma and gastric juice ascorbic acid concentrations in patients with and without H. pylori infection and also before and after its eradication. Gastric juice ascorbic acid concentrations in the H. pylori-positive patients were significantly lower than in the H-negative controls despite similar plasma ascorbic acid concentrations in the two groups. After eradication of H. pylori, gastric juice ascorbic acid increased to near normal levels. Nitrites and N-nitroso compounds have been implicated in gastric carcinogenesis39. Atrophic gastritis, caused by chronic H. pylori infection, results in hypochlorhydria-a condition that leads to bacterial overgrowth. Nitratereducing bacteria may convert nitrate to nitrite, which may be metabolized to N-nitroso compounds. Reactive oxygen species damage DNA, causing strand breaks, translocations and deletions4. H. pylori-associated inflammation causes excessive production of reactive oxygen species which may result in DNA injury in stem cells. After successful eradication of H. pylori, the reactive oxygen species activity is substantially reduced41. In summary, H. pylori infection causes a reduction of ascorbic acid secretion, an accumulation of N-nitroso compounds and enhanced production of reactive oxygen species.

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BACTERIAL PATHOGENICITY The clinical outcome of H. pylori infection is very variable. Most hosts remain symptom-free, some develop peptic

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ulcers and very few progress to gastric cancer. H. pylori strains may differ in their virulence. Antibodies against a H. pylori protein can be detected in gastric biopsies of H. pyloriinfected individuals and are strongly associated with peptic ulcer disease and severe gastritis42. These antibodies are associated with the presence of the cytotoxin associated gene (cagA). Strains that express the cagA-antigen induce more rapid secretion of interleukin-8 (IL-8) in gastric epithelial cell lines than do cagA-negative strains43. Gastric epithelial IL-8 expression is increased in chronic H. pylor-associated gastritis and in gastric carcinoma44. Certain strains of H. pylori produce a vacuolating cytotoxin that induces cytopathic vacuolation in gastric epithelial cell lines. The gene encoding for this toxin is known as vacA45 and its mosaic structure has been determined. It consists of one of two signal sequence types, sI and s2, and one of two mid-region types, ml and m2. In areas of high gastric cancer incidence, the signal sequence type si is more common than in areas with low rates of gastric cancer46. Strains possessing the s 1 signal sequence seem to be more virulent and may play an important role in the development of gastric cancer. HELICOBACTER PYLORI AND GASTRIC LYMPHOMA Primary non-Hodgkin's lymphomas of the stomach account for 1-7% of all gastric malignancies. Mucosa-associated lymphoid tissue is not found in the normal stomach. Chronic H. pylori infection, however, results in a lymphocytic

infiltrate and the formation of lymphoid follicles47. Eradication of H. pylori leads to regression of these changes48. Epidemiological studies, based on stored serum samples, suggest that patients with low-grade B-cell mucosaassociated lymphoid tissue (MALT) lymphoma are more likely to be infected with H. pylori than matched controls49. In vitro, cells from low-grade B-cell MALT lymphomas are H. pylori and T-cell dependent50. In an intervention study, Wotherspoon et al.51 gave H. pylori eradication therapy to six patients with histological and molecular genetic evidence of low-grade B-cell MALT lymphoma and concomitant H. pylori infection. H. pylori was successfully eradicated in all six. After repeated biopsies 4-10 months after eradication, five of the patients showed no evidence of lymphoma. In the largest and most recent study52, 33 patients with low-grade B-cell MALT lymphoma, associated with H. pylori-gastritis, were treated with eradication therapy. All became H. pylori-negative. On histological assessment 23 patients showed complete regression and four partial regression of lymphoma. During a 1 year follow-up there were no relapses. Long-term followup studies, however, are needed to determine whether these remissions are lasting.

JOURNAL OF THE ROYAL SOCIETY

CANCER PREVENTION

Two strategies for the prevention of gastric cancer through control of H. pylori have been proposed. Vaccination is a long-term prospect and, as yet, no vaccine is available. It would need to be administered early in life and, as gastric cancer usually occurs late in life, at least 50 years would elapse before any benefits were apparent. Effective and inexpensive regimens are now becoming available for eradication of H. pylori. Thus we can consider screening large populations and treating those infected as a means of cancer prevention. Screening programmes would employ non-invasive methods for H. pylori detection. Serological testing for IgG antibodies against H. pylori has its disadvantages since a positive result may indicate previous infection. The 13C urea breath test is highly sensitive and specific and does not expose the patient to radiation. This test has been modified to render it user-friendly and ideal for a screening programme53. For any screening strategy to be cost-effective several factors must be taken into account. The prevalence of H. pylori infection is decreasing and this decline is accompanied by a parallel decrease in the incidence of gastric cancer. It would be necessary to establish a screening programme in an age group sufficiently old that reinfection would not occur and sufficiently young that eradication would still have a beneficial effect on cancer prevention. Clearly more research is needed in drug development and in determination of the natural history of H. pyloriassociated gastric cancer in order to optimize any screening strategy. However, with the knowledge that H. pylori results in a ninefold increased risk for the development of the world's second most commonly diagnosed fatal cancer, screening in symptom-free individuals cannot be far over the medical horizon.

REFERENCES I Parkin DM, Pisani P, Fearly J. Estimates of worldwide incidence of eighteen major cancers in 1985. IntJ Cancer 1993;54:594-606 2 Rugge M, Sonego F, Panozzo M, et al. Pathology and ploidy in the prognosis of gastric cancer with no extranodal metastasis. Cancer 1994;73: 1127-33 3 Lauren P. The two histological main types of gastric carcinoma: diffuse and so-called intestinal type carcinoma. An attempt at a histoclinical classification. Acta Pathol ilicrobiol Scand 1965;64:31-49 4 Correa P. A human model of gastric carcinogenesis. Cancer Res

1988;48:3554-66 5 Correa P. Human gastric carcinogenesis: a multistep and multifactorial process. Cancer Res 1992;52:6735-40 6 International Agency for Research on Cancer. Schistosomes, Liver Flukes and Helicobacter pylori. IARC monographs on the evaluation of carcinogenic risks to humans, vol 61, Lyon: IARC, 1994 7 Perez-Perez GI, Taylor DN, Bodhidatta L, et al. Seroprevalence of Helicobacter pyloni infections in Thailand. ] Infrct Disease 1990; 161: 1237-41

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8 EUROGAST Study Group. An international association between Helicobacter plori infection and gastric cancer. Lancet 1994;341:1359-62 9 The Gastrointestinal Physiology Working Group. Helicobacter pylori and gastritis in Peruvian patients: relationship to socioeconomic level, age and sex. Am J Gastroenterol 1990;85:819-23 10 Parsonnet J. Helicobacter pylori and gastric cancer. Gastroenterol Clin N Am 1993;22:89-104 11 Sipponen P, Seppala K. Long-term consequences of H. pylori infection: time trends in H. pylori gastritis, gastric cancer and peptic ulcer disease. In: Hunt RH, Tytgat GNJ, eds. Helicobacter pylori: Basic Mechanisms to Clinical Cure. Boston: Kluwer 1994:372-80 12 Parsonnet DM, Friedman GT, Vandersteen DP, et al. Helicobacter pylori infection and risk for gastric carcinoma. N Engi J Med 1991;325:1127-31 13 Forman D, Newell DG, Fullerton F, et al. Association between infection with Helicobacter pylori and risk of gastric cancer; evidence of a prospective investigation. BMJ 1991 ;302:1302-5 14 Nomura A, Stemmerman GN, Chyou PH, Kato I, Perez-Perez GI, Blaser MJ. Helicobacter pylori infection and gastric carcinoma among Japanese Americans in Hawaii. N EngiJ Med 1991;325: 1132-6 15 Forman D, Webb P, Parsonnet J. Helicobacter pylori and gastric cancer. Lancet 1994;343:243-4 16 Tally NJ, Zinsmeister AR, Weaver A, Dimagno EP, Carpenter HA, Perez-Perez, GI, et al. Gastric adenocarcinoma and Helicobacter pylori infection. J NatI Cancer Inst 1991;83:1734-9 17 Sipponen P, Kosunen TU, Valle J, Riihela M, Seppala K. Helicobacter pylori infection and chronic gastritis in gastric cancer. J Clin Pathol 1992;45:319-23 18 Hansson LE, Engstrand L, Nyren OL, et al. Helicobacter pylori infection: independent risk indicator of gastric adenocarcinoma. Gastroenterology 1993; 105:1098-103 19 Kuipers EJ, Gracia-Casanova M, Pena AS, et al. Helicobacter pylori serology in patients with gastric carcinoma. Scand J Gastroenterol 1993;28:433-7 20 Warren JR. Unidentified curved bacilli on gastric epithelium in active chronic gastritis. Lancet 1983;i: 1273-5 21 Blaser MJ. Gastric Campylobacter-like organisms, gastritis and peptic ulcer disease. Gastroenterology, 1987;93:371-83 22 Rauws EAJ, Langenberg W, Houthoff HJ, Zanen HC, Tytgat GNJ. Campylobacter pyloridis-associated active antral gastritis: a prospective study of its prevalence and the effect on anti-bacterial and anti-ulcer treatment. Gastroenterology 1988;94: 33-40 23 Dixon MF. Campylobacter pylori and chronic gastritis. In: Rathbone BJ, Heatley RV, eds. Campylobacter pylori and Gastroduodenal Disease. Oxford: Blackwell Scientific Publications, 1989:106-16 24 Craanen ME, Blok P, Dekker W, Fewerda J, Tytgat GNJ. Intestinal metaplasia and Helicobacter pylori: an endoscopic-bioptic study of the antrum. Gut 1992;33:16-20

25 Filipe MI. Histochemistrv of intestinal mucins. In: Whitehead R, ed. Gastrointestinal and Oesophageal Pathology. Edinburgh: Churchill Livingstone, 1989: 71 26 Rokkas T, Filipe MI, Sladen GE. Detection of an increased incidence of early gastric cancer in patients with intestinal metaplasia type III Who are closely followed up. Gut 1991;32:1110-13 27 O'Connor F, Sweeney E, O'Morain C. Helicobacter pylori and subtypes of intestinal metaplasia in gastric antral mucosa. Irish J Med Sci 1995;74:225-6 28 Gilvarry JM, Leen E, Sweeney E, O'Morain C. The long term effect of Helicobacter pylori on gastric mucosa. Eur J Gastroenterol Hepatol 1994;6:43-5 29 Fujiwara Y, Kang J, Fujiwara K, Chang K, Tarnawksi A. Effects of non-steroidal anti-inflammatory drugs on cell proliferation in gastroduodenal mucosa. A review article. Eur J Gastroenterol Hepato1 1993;5:301-5

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30 Broek D, Bartlett R, Crawford K, Nurse P. Involvement of p34cdc2 in establishing the dependency of S phase on mitosis. Nature 1991 ;349:388-93 31 Hollywood DP, Lemoine NR. Growth factors, oncogenes and tumour suppressor genes. In: Hall P, Levison DA, Wright NA, eds. Assessment of Cell Proliferation in Clinical Prattice. London: Springer-Verlag, 1992:27-41 32 Cahill RJ, Sant S, Beattie S, Hamilton H, O'Morain C. Helicobaater pylori and increased epithelial cell proliferation: a risk factor for cancer. EurJ Gastroenterol Hepatol 1994;6: 1123-8 33 Cahill RJ, Sant S, Beattie S, Hamilton H, O'Morain C. Effect of eradication of Helicobacaer pylori infection on gastric epithelial cell proliferation. Dig Dis Sci 1995;40: 1627-31 34 Cahill RJ, Kilgallen C, Beattie S, Hamilton H, O'Morain C. Gastric epithelial cell kinetics in the progression from normal mucosa to gastric carcinoma. Gut 1996;38:177-81 35 Freeman JT, Hafkesbring R. Comparative studies of ascorbic acid levels in gastric secretion and blood. Gastroenterology 1957;32:878-86 36 Hansson LE, Myren 0, Bergstrom R, et al. Nutrients and gastric cancer risk. A population based control study in Sweden. Int J Cancer

1994;57:638-44 37 O'Connor HJ, Schorah CJ, Habibzedah N, Axon ATR, Cockel R. Vitamin C in the human stomach: relation to gastric pH, gastroduodenal disease and possible sources. Gut 1989;30:436-42 38 Bannerjee S, Hawksby C, Miller S, Dahill S, Beattie AD, McColl KEL. Effect of Helicobacter pylori and its eradication on gastric juice ascorbic acid. Gut 1994;35:317-22 39 Correa P, Haenszel W, Cuello C, Tannenbaum SR, Archer M. A model for gastric cancer epidemiology. Lancet 1975;ii:58-60 40 Koningsberger JC, Marx JJM, Van Hattum J. Free radicals in gastroenterology. ScandJ Gastroenterol 1988;23(suppl 154):30-40 41 Drake IM, Warland D, Carswell N, et al. Reactive oxygen species (ROS) activity and damage in Helicobacter pylori-associated gastritis (HPG)-effect of eradication therapy. Gut 1995;37(suppl l):A155

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42 Crabtree JE, Taylor JD, Wyatt JI, et a). Mucosal IgA recognition of Helicobacter pyloA 120 kDa protein, peptic ulceration and gastric pathology. Lancet 1991; 338:332-5 43 Crabtree JE, Farmery S, Lindley IJD, Peichl P, Tompkins DS. Cytotoxic strains of Helicobacter pylori induce IL-8 production form gastric epithelial cells (Abstr). Acta Gastroenterol Belg 1993; 56(suppl):48 44 Crabtree JE, Wyatt JI, Trejdosiewicz LK, et al. Interleukin 8 expression in Helicobacter pylori infected, normal and neoplastic gastroduodenal mucosa. J Clin Pathol 1994;47:61-7 45 Wyatt JI, Rathbone BJ. Immune response of the gastric mucosa to Campylobacter pylori. Scand J Gastroenterol 1989;23(suppl 154):44-9 46 Telford JL, Ghiara P, Dell'orco M, et al. Gene structure of the Helicobacter pylori cytotoxin and evidence of its key role in gastric disease. J Exp Med 1994;179:1653-8 47 Atherton JC, Cover TL, Ray KC, Peek RM, Perez-Perez, GI, Blaser MJ. Genotypic analysis of vacA and cagA in Helicobacaer pylori isolates from the U.S., Thailand, Peru and China. Gut 1995;37(suppl 1): A275 48 Stolte M, Edti S. Lymphoid follicles in the antral mucosa: immune response to Campylobacter pylori. J Clin Pathol 1989;42: 1269-71 49 Parsonnet J, Hansen S, Rodriguez L, et al. Helicobacter pylori infection in gastric lymphoma. N Eng]J Med 1994;330:1267-71 50 Hussell T, Isaacson PG, Crabtree JE. The response of cells from lowgrade B-cell gastric lymphoma of mucosa-associated lymphoid tissue to Helicobacter pylori. Lancet 1993;342:571-4 51 Wotherspoon AC, Doglioni C, Diss TC. Regression of primary lowgrade-B-cell lymphoma of mucosa-associated lymphoid tissue after eradication of Helicobacter pylori. Lancet 1993;342:575-7 52 Bayerdorffer E, Neubauer A, Rudolph B, et al. Regression of primary gastric lymphoma of mucosa-associated lymphoid tissue type after cure of Helicobacter pylori infection. Lancet 1995;345: 1591-4 53 Buckley M, Hamilton H, Beattie S, O'Morain C. A simplified reliable urea breath test. Gut 1995;37(suppl 1):A242