|
Advertisement |
|
|
||
 |
|
|||||
|
|||||
|
 |
||||||
|
||||||
|
||||||
|
Journal of Clinical Oncology, Vol 24, No 27 (September 20), 2006: pp. 4434-4440 © 2006 American Society of Clinical Oncology. DOI: 10.1200/JCO.2005.04.1459 MDM2 Promoter Polymorphism Is Associated With Both an Increased Susceptibility to Gastric Carcinoma and Poor Prognosis
From the Department of Gastroenterology, Nagoya University Graduate School of Medicine; and the Department of Endoscopy, Nagoya University Hospital, Nagoya, Japan Address reprint requests to Naoki Ohmiya, MD, PhD, Department of Gastroenterology, Nagoya University Graduate School of Medicine, 65 Tsuruma-cho, Showa-ku, Nagoya, Japan 466-8550; e-mail: nohmiya{at}med.nagoya-u.ac.jp
PURPOSE: Recently, a single-nucleotide polymorphism in the MDM2 promoter (SNP309) has been found to lower the age of onset of tumors and increase the occurrence of multiple primary tumors in Li-Fraumeni syndrome, and accelerate the development of sporadic adult soft tissue sarcoma. The aim of this study was to determine whether SNP309 is associated with susceptibility to gastric carcinoma and its prognosis. PATIENTS AND METHODS: In a case-control study including 438 controls and 410 patients with sporadic gastric carcinoma, MDM2 SNP309 was genotyped. Serum pepsinogens (PGs) I and II were measured in 438 control subjects and 253 cases selected from 410 patients. Tumor tissue was immunostained with p53 and examined for mutations in exons 5 to 8 of p53 using polymerase chain reaction–based single strand conformational polymorphism analysis and direct sequencing. RESULTS: The risk of overall gastric carcinoma for SNP309 (G/G) was significantly increased when compared with T carriers (P = .039), especially carcinomas with extragastric tumors (P = .005), carcinoma with severe atrophic gastritis positive for PG assay (PG I level < 70 ng/mL and PG I/II < 3.0; P = .005), antral carcinoma (P = .020), intestinal-type carcinoma (P = .023), p53-immunopositive carcinoma (P = .007), and carcinoma with p53 mutations (P = .007). No significant difference in age at diagnosis was observed among genotypes. SNP309 (G/G) was an independent marker of poor overall survival in advanced carcinoma (hazard ratio, 3.16; 95% CI, 1.22 to 8.20; P = .018). CONCLUSION: This study provides evidence supporting the association of SNP309 with gastric carcinogenesis via p53 tumor suppressor pathway, extragastric tumorigenesis, and poor prognosis.
The tumor suppressor protein, p53, is activated on cellular stresses such as DNA damage and oncogene activation, and initiates a transcriptional program which leads to DNA repair, cell cycle arrest, and in some cases, apoptosis.1 Inactivating mutations of the p53 gene occur in half of all cancers.2 MDM2 is an important negative regulator of p53. MDM2 directly binds to and inhibits p53 by regulating its location, stability, and activity as a transcriptional activator.3 Recently, a T to G change at the 309th nucleotide in the first intron of the MDM2 gene (SNP309) has been found and shown to increase the affinity of the transcriptional activator Sp1, resulting in higher levels of MDM2 RNA and protein and the subsequent attenuation of the p53 pathway. The presence of SNP309 lowers the age of onset of tumors and increases the occurrence of multiple primary tumors in a lifetime in humans who carry a germline inactivating mutation in one p53 allele (Li-Fraumeni syndrome). Individuals homozygous for SNP309 in the MDM2 gene without a germline p53 mutation develop sporadic adult soft tissue sarcoma on average 12 years earlier than those without SNP309.4 Approximately 20% of sporadic soft-tissue sarcomas harbors p53 mutations5 and overexpression of p53 and MDM2 proteins are correlated with poor survival.6 Gastric carcinoma also harbors frequent somatic genetic changes at p53, mostly G:C > A:T transitions,7 which may be induced by nitric oxide8,9 and N-nitrosocompounds found in food.10 These mutations are an early event of gastric carcinogenesis especially for intestinal types through atrophy-metaplasia-carcinoma pathways.11,12 Infection with Helicobacter pylori has been associated with chronic atrophic gastritis13 and subsequent risk of gastric carcinoma.14,15 Virulence factors of H pylori contribute to the exacerbation of gastric mucosal damage and some studies have demonstrated a significant association of vacA16 and cagA17 genotypes and gastric carcinoma. On the other hand, it has been reported that although their subtypes determined by cagA, vacA genotypes, and iceA alleles are geographically different, the presence of their virulence does not predict the risk for symptomatic clinical outcomes.18,19 Host genetic factors such as cytokine gene polymorphisms in interleukin (IL) -1B, IL-1RN, IL-10, and tumor necrosis factor-A genes has been reported to increase the risk of noncardia gastric carcinoma in white patients.20 The other studies, however, have reported no such association in Asians.21,22 In this study, we focused on the core regulation component of the p53 tumor suppressor pathway that plays a critical role in safeguarding the integrity of the genome, and elucidated the association between host genetic factor of MDM2 SNP309 and susceptibility to gastric carcinoma in a case-control study. We further determined its genetic effects on p53 alterations using immunohistochemistry and mutational analysis, and prognosis of gastric carcinoma.
Study Population The study was performed in ethnically and sex-matched subjects without gastric tumors (n = 438; control group) and patients with gastric carcinoma (n = 410; gastric carcinoma group). The controls were apparently healthy individuals and were recruited from health checkup examinees who had undergone gastroscopy and/or double-contrast barium meal radiography as part of a screening program for gastric carcinoma from January to March 2000 at Aichi Prefectural Health Care Center, Japan. Gastric tumors were excluded by endoscopy or radiography in the control group. All subjects were Japanese, and none of them had a history of gastric carcinoma. Genotype frequencies of polymorphisms in several unrelated cytokine genes in this control group did not deviate significantly from those expected under Hardy-Weinberg equilibrium as described previously.23,24 The gastric carcinoma group consists of a series of patients, who were admitted to Nagoya University Hospital between January 1999 and February 2005. Pathologic diagnosis and classification of the surgically or endoscopically resected carcinoma was made according to the Laurén classification.25 Each subject was interviewed about history of gastric and other tumors. All subjects in the controls and cases who had undergone eradication of H pylori were excluded. With respect to prognosis, causes of death, except gastric carcinoma or extragastric tumors, were included in censor data. No patients met the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer26 or criteria for the diagnosis of classical Li-Fraumeni27 or Li-Fraumeni–like syndrome.28 This study was reviewed and approved by the institutional review board and Ethics Committee of Nagoya University School of Medicine. Informed consent was obtained from all subjects and patients. The characteristics of the study population are presented in Table 1.
Blood Samples Genomic DNA and fasting serum of each subject were isolated from blood samples collected in the morning. DNA was extracted as described previously.23 Serum samples were obtained from the gastric carcinoma group before resection.
Measurements of Serum Pepsinogens I, II, and H pylori IgG Antibody
Genotyping of SNP309 in the MDM2 Promoter and Cytokine Gene Polymorphisms
Tissue Samples Paraffin-embedded cancerous sections were obtained in 208 patients, who were admitted to our hospital between January 1999 and December 2001 and were subject to p53 immunohistochemical analysis. Cancerous and surrounding normal tissues were obtained from surgically resected fresh frozen specimens in 113 patients, and microdissected from paraffin-embedded sections in 87 patients, who were admitted to our hospital between January 1999 and December 2001. DNA was extracted as described previously30 and subject to p53 mutational analysis.
Immunohistochemical Analysis of p53
p53 Mutational Analysis
Statistical Analysis
MDM2 SNP309 in the Control Group Genotype frequencies of SNP309 did not deviate significantly from those expected under the Hardy-Weinberg equilibrium. H pylori seropositivity; PG I and PG II levels, and PG I-II ratio; positivity of PG assay; and incidence of extragastric tumors were not significantly different among genotypes. PG I and PG II levels, and PGI-II ratio, and positivity of PG assay in H pylori–seropositive subjects were not different either (data not shown).
MDM2 SNP309 in the Gastric Carcinoma Group
With respect to prognosis, the gastric carcinoma patients homozygous for SNP309 (G/G) showed a significant association of poor overall survival in 160 patients with TNM stages IB (T1N1M0 or T2N0M0) to IV (T4N1-3M0, T1- to T3N3M0, or any NM1; P = .026, Fig 1A). There was no association of survival among SNP309 genotypes in 209 patients with stage IA (Fig 1B) disease. Cox proportional hazards analysis to adjust for TNM stage, age, sex, extragastric tumor, and concomitant chemotherapy showed that SNP309 (G/G) was an independent marker of poor prognosis for gastric carcinoma with TNM IB-IV stages (hazard ratio, 3.16; 95% CI, 1.22 to 8.20; P = .018). High TNM stage certainly showed a strong association of poor overall survival (hazard ratio, 3.73; 95% CI, 2.48 to 5.60; P < .0001).
MDM2 SNP309 has been shown to associate with elevated risk of tumor formation in patients with Li-Fraumeni syndrome and sporadic adult soft tissue sarcoma.4 As the tumor suppressor p53 gene is mutated in approximately 20% to 65% of gastric carcinoma,32 it is postulated that this polymorphism potentially associates with the development of gastric carcinoma. The present study supported this hypothesis in that MDM2 SNP309 held an elevated risk of overall sporadic gastric carcinomas, especially those harboring p53 mutations and complicated with extragastric tumors, though the age at diagnosis was not different among genotypes. The finding that MDM2 SNP309 accelerated the gastric carcinomas especially harboring p53 mutations offers one possible mechanisms. Approximately 50% of all cancers involve missense mutations of one p53 allele coupled with a deletion of the second allele,2 besides specific mutations that drive cotranslated wild-type p53 protein into the mutant conformation with a dominant negative effect.33 Allelic deletion of p53 is preceded by the mutational events and a late event in gastric carcinogenesis.34 The presence of SNP309 in the MDM2 gene leads to higher expression of the MDM2 protein, which inhibits p534 and thereby can substitute for p53 LOH or another mutation. One p53 mutation in a MDM2 SNP309 G homozygote may not require a second event to result in loss of function and subsequent carcinoma development. Our result that patients with gastric carcinoma homozygous for SNP309 (G/G) are likely to develop another extragastric tumor when compared with T carriers is consistent with the finding that SNP309 increased occurrence of multiple primary tumors of the Li-Fraumeni syndrome in a lifetime.4 Hereditary nonpolyposis colorectal cancer syndrome is transmitted as an autosomal dominant trait caused by germline mutation of mismatch repair genes,35-37 and also predisposes to cancers of multiple organs such as colon, endometrium, stomach, ureter, renal pelvis, ovary, and small bowel.38 However, no patients met the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer26 in this study. No patients met the criteria for the diagnosis of classical Li-Fraumeni27 or Li-Fraumeni–like syndromes,28 but patients homozygous and heterozygous for SNP309 (G/G and T/G) developed liposarcoma, breast carcinoma, adrenal, and brain tumors as observed in Li-Fraumeni and Li-Fraumeni–like syndromes, whereas those wild-type for SNP309 (T/T) did not in this study. This polymorphism might predispose to subgroup of tumors in multiple organs through a molecular pathway similar to those in Li-Fraumeni and Li-Fraumeni–like syndromes. Although SNP309 was associated with susceptibility to both carcinoma with p53 mutations and p53-immunopositive carcinoma, correlation between p53 mutations and protein expression was not significant in the present study. Singer et al reported that p53 immunoreactivity is generally higher in specimens containing mutant p53, but immunostaining is neither sufficiently specific nor sensitive enough to predict p53 mutations.39 Positive p53 immunostaining without detectable mutations may result from failures of the normal degradative p53 pathways so that wild-type protein accumulates in the nucleus or it accumulates when there is upregulation of the gene in response to cellular environmental stresses.32 Negative p53 immunostaining with detectable mutations may result from nonsense or frameshift mutations. The next finding in this study was that SNP309 can impact tumorigenesis especially in the severe atrophic gastritis positive for PG assay and associates with intestinal-type carcinoma, though this polymorphism did not affect susceptibility to gastric atrophy in controls. Lower PG I level and PGI-II ratio is highly specific for severe atrophic gastritis,40 and PG assay such as PGI level less than 70 ng/mL and PGI-II ratio less than 3.0 has been reported to be helpful for gastric carcinoma screening, especially of the intestinal type.29 H pylori causes chronic active inflammation of the gastric mucosa in the majority of colonized subjects, and in approximately 40% to 50% of infected subjects, will eventually lead to the establishment of gastric atrophy and metaplasia. The presence of these consecutive changes leads to an increased risk for carcinoma of the distal stomach, in particular of the intestinal type.12,41 The onset of this carcinoma requires the phenotypic and genotypic transformation including p53 mutations in a multistep process for a longer latency period than that of carcinoma of diffuse type, and with no p53 mutations.11,42 The present result suggested SNP309 elevated the risk for carcinoma in the stomach after the establishment of atrophic gastritis. Therefore, the age at diagnosis with gastric carcinoma may not have been distinct among SNP309 genotypes. SNP309 was shown to independently predict poor prognosis of advanced gastric carcinoma in this study. The prognostic value of p53 mutations or p53 protein accumulation has not been consistently demonstrated in gastric carcinoma.43 Many reports, however, demonstrated that p53 alteration was correlated with shortened survival of patients with gastric carcinoma.43-45 Since the tumor cells with mutant p53 have been reported to show attenuated apoptosis, mutations in p53 may cause chemoresistance and therefore adversely affect the prognosis of tumor.46 SNP309 was associated with susceptibility to gastric carcinoma immunopositive for p53 and with p53 mutations; it may thereby be indicative of poor survival. If our findings are corroborated in larger and other ethnic series samples, appropriate treatments, surveillance, and preventive measures could be formulated according to SNP309 genotypes. As SNP309 homozygote (G/G) was only present in 30% of gastric carcinoma in Japanese patients, genotyping of SNP309 in combination with other markers would be more helpful.
The authors indicated no potential conflicts of interest.
We thank Yasuhiro Kodera, MD, PhD, Michitaka Fujiwara, MD, PhD, Department of Surgery II, and Norihiro Yuasa, MD, PhD, Department of Surgery I, Nagoya University Graduate School of Medicine for tissue sampling and follow-up data, Tetsuro Nagasaka, MD, PhD, Department of Laboratory Medicine, Nagoya University Hospital for p53 immunostaining, and John Cole for proofreading.
Presented in poster format at the American Gastroenterological Association (DDW 2006), Los Angeles, CA, May 24, 2006. Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.
1. Jin S, Levine AJ: The p53 functional circuit. J Cell Sci 114:4139-4140, 2001 2. Hollstein M, Sidransky D, Vogelstein B, et al: p53 mutations in human cancers. Science 253:49-53, 1991 3. Michael D, Oren M: The p53-Mdm2 module and the ubiquitin system. Semin Cancer Biol 13:49-58, 2003[CrossRef][Medline] 4. Bond GL, Hu W, Bond EE, et al: A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans. Cell 119:591-602, 2004[CrossRef][Medline] 5. Schneider-Stock R, Radig K, Oda Y, et al: p53 gene mutations in soft-tissue sarcomas: Correlations with p53 immunohistochemistry and DNA ploidy. J Cancer Res Clin Oncol 123:211-218, 1997[Medline] 6. Cordon-Cardo C, Latres E, Drobnjak M, et al: Molecular abnormalities of mdm2 and p53 genes in adult soft tissue sarcomas. Cancer Res 54:794-799, 1994 7. Renault B, van den Broek M, Fodde R, et al: Base transitions are the most frequent genetic changes at P53 in gastric cancer. Cancer Res 53:2614-2617, 1993 8. Nguyen T, Brunson D, Crespi CL, et al: DNA damage and mutation in human cells exposed to nitric oxide in vitro. Proc Natl Acad Sci U S A 89:3030-3034, 1992 9. Wink DA, Kasprzak KS, Maragos CM, et al: DNA deaminating ability and genotoxicity of nitric oxide and its progenitors. Science 254:1001-1003, 1991 10. Sugimura T, Kawachi T: Experimental stomach cancer. Methods Cancer Res 7:245-308, 1973 11. Correa P, Shiao YH: Phenotypic and genotypic events in gastric carcinogenesis. Cancer Res 54:1941s-1943s, 1994 12. Ohata H, Kitauchi S, Yoshimura N, et al: Progression of chronic atrophic gastritis associated with Helicobacter pylori infection increases risk of gastric cancer. Int J Cancer 109:138-143, 2004[CrossRef][Medline] 13. Biasco G, Paganelli GM, Vaira D, et al: Serum pepsinogen I and II concentrations and IgG antibody to Helicobacter pylori in dyspeptic patients. J Clin Pathol 46:826-828, 1993 14. Nomura A, Stemmermann GN, Chyou PH, et al: Helicobacter pylori infection and gastric carcinoma among Japanese Americans in Hawaii. N Engl J Med 325:1132-1136, 1991[Abstract] 15. Parsonnet J, Friedman GD, Vandersteen DP, et al: Helicobacter pylori infection and the risk of gastric carcinoma. N Engl J Med 325:1127-1131, 1991[Abstract] 16. Van Doorn LJ, Figueiredo C, Megraud F, et al: Geographic distribution of vacA allelic types of Helicobacter pylori. Gastroenterology 116:823-830, 1999[CrossRef][Medline] 17. Basso D, Navaglia F, Brigato L, et al: Analysis of Helicobacter pylori vacA and cagA genotypes and serum antibody profile in benign and malignant gastroduodenal diseases. Gut 43:182-186, 1998 18. Maeda S, Ogura K, Yoshida H, et al: Major virulence factors, VacA and CagA, are commonly positive in Helicobacter pylori isolates in Japan. Gut 42:338-343, 1998 19. Yamaoka Y, Kodama T, Gutierrez O, et al: Relationship between Helicobacter pylori iceA, cagA, and vacA status and clinical outcome: Studies in four different countries. J Clin Microbiol 37:2274-2279, 1999 20. El-Omar EM, Rabkin CS, Gammon MD, et al: Increased risk of noncardia gastric cancer associated with proinflammatory cytokine gene polymorphisms. Gastroenterology 124:1193-1201, 2003[CrossRef][Medline] 21. Wu MS, Wu CY, Chen CJ, et al: Interleukin-10 genotypes associate with the risk of gastric carcinoma in Taiwanese Chinese. Int J Cancer 104:617-623, 2003[CrossRef][Medline] 22. Chang YW, Jang JY, Kim NH, et al: Interleukin-1B (IL-1B) polymorphisms and gastric mucosal levels of IL-1beta cytokine in Korean patients with gastric cancer. Int J Cancer 114:465-471, 2005[CrossRef][Medline] 23. Ohyama I, Ohmiya N, Niwa Y, et al: The association between tumour necrosis factor-alpha gene polymorphism and the susceptibility to rugal hyperplastic gastritis and gastric carcinoma. Eur J Gastroenterol Hepatol 16:693-700, 2004[CrossRef][Medline] 24. Taguchi A, Ohmiya N, Shirai K, et al: Interleukin-8 promoter polymorphism increases the risk of atrophic gastritis and gastric cancer in Japan. Cancer Epidemiol Biomarkers Prev 14:2487-2493, 2005 25. Laur'En P: The two histological main types of gastric carcinoma: Diffuse and so-called intestinal-type carcinoma—An attempt at a histo-clinical classification. Acta Pathol Microbiol Scand 64:31-49, 1965[Medline] 26. Vasen HF, Watson P, Mecklin JP, et al: New clinical criteria for hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) proposed by the International Collaborative group on HNPCC. Gastroenterology 116:1453-1456, 1999[CrossRef][Medline] 27. Li FP, Fraumeni JF Jr, Mulvihill JJ, et al: A cancer family syndrome in twenty-four kindreds. Cancer Res 48:5358-5362, 1988 28. Birch JM, Hartley AL, Tricker KJ, et al: Prevalence and diversity of constitutional mutations in the p53 gene among 21 Li-Fraumeni families. Cancer Res 54:1298-1304, 1994 29. Kitahara F, Kobayashi K, Sato T, et al: Accuracy of screening for gastric cancer using serum pepsinogen concentrations. Gut 44:693-697, 1999 30. Ohmiya N, Matsumoto S, Yamamoto H, et al: Germline and somatic mutations in hMSH6 and hMSH3 in gastrointestinal cancers of the microsatellite mutator phenotype. Gene 272:301-313, 2001[CrossRef][Medline] 31. Niimi C, Goto H, Ohmiya N, et al: Usefulness of p53 and Ki-67 immunohistochemical analysis for preoperative diagnosis of extremely well-differentiated gastric adenocarcinoma. Am J Clin Pathol 118:683-692, 2002[CrossRef][Medline] 32. Fenoglio-Preiser CM, Wang J, Stemmermann GN, et al: TP53 and gastric carcinoma: A review. Hum Mutat 21:258-270, 2003[CrossRef][Medline] 33. Milner J, Medcalf EA: Cotranslation of activated mutant p53 with wild type drives the wild-type p53 protein into the mutant conformation. Cell 65:765-774, 1991[CrossRef][Medline] 34. Rhyu MG, Park WS, Jung YJ, et al: Allelic deletions of MCC/APC and p53 are frequent late events in human gastric carcinogenesis. Gastroenterology 106:1584-1588, 1994[Medline] 35. Leach FS, Nicolaides NC, Papadopoulos N, et al: Mutations of a mutS homolog in hereditary nonpolyposis colorectal cancer. Cell 75:1215-1225, 1993[CrossRef][Medline] 36. Bronner CE, Baker SM, Morrison PT, et al: Mutation in the DNA mismatch repair gene homologue hMLH1 is associated with hereditary non-polyposis colon cancer. Nature 368:258-261, 1994[CrossRef][Medline] 37. Papadopoulos N, Nicolaides NC, Wei YF, et al: Mutation of a mutL homolog in hereditary colon cancer. Science 263:1625-1629, 1994 38. Lynch HT, Smyrk TC, Watson P, et al: Genetics, natural history, tumor spectrum, and pathology of hereditary nonpolyposis colorectal cancer: An updated review. Gastroenterology 104:1535-1549, 1993[Medline] 39. Singer G, Stohr R, Cope L, et al: Patterns of p53 mutations separate ovarian serous borderline tumors and low- and high-grade carcinomas and provide support for a new model of ovarian carcinogenesis: A mutational analysis with immunohistochemical correlation. Am J Surg Pathol 29:218-224, 2005[CrossRef][Medline] 40. Samloff IM, Varis K, Ihamaki T, et al: Relationships among serum pepsinogen I, serum pepsinogen II, and gastric mucosal histology: A study in relatives of patients with pernicious anemia. Gastroenterology 83:204-209, 1982[Medline] 41. Kuipers EJ: Review article: Exploring the link between Helicobacter pylori and gastric cancer. Aliment Pharmacol Ther 13(suppl 1):3-11, 1999 42. Rugge M, Shiao YH, Busatto G, et al: The p53 gene in patients under the age of 40 with gastric cancer: Mutation rates are low but are associated with a cardiac location. Mol Pathol 53:207-210, 2000 43. Dowell SP, Hall PA: The p53 tumour suppressor gene and tumour prognosis: Is there a relationship? J Pathol 177:221-224, 1995[CrossRef][Medline] 44. Lim BH, Soong R, Grieu F, et al: p53 accumulation and mutation are prognostic indicators of poor survival in human gastric carcinoma. Int J Cancer 69:200-204, 1996[CrossRef][Medline] 45. Kubicka S, Claas C, Staab S, et al: p53 mutation pattern and expression of c-erbB2 and c-met in gastric cancer: Relation to histological subtypes, Helicobacter pylori infection, and prognosis. Dig Dis Sci 47:114-121, 2002[CrossRef][Medline] 46. Kirsch DG, Kastan MB: Tumor-suppressor p53: Implications for tumor development and prognosis. J Clin Oncol 16:3158-3168, 1998 Submitted September 5, 2005; accepted July 24, 2006. This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||
|
|||||||||||
|
|
Copyright © 2006 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|
TOP
ABSTRACT
INTRODUCTION
2 statistics. Comparison of age between cases and controls was assessed by the Mann-Whitney U test. Comparison of sex, extragastric tumors, H pylori infection, and SNP309 genotype frequencies between cases and controls was assessed by 
