Association between TLR4 (+896A/G and +1196C/T) Polymorphisms and Gastric Cancer Risk: An Updated Meta-Analysis
et al. (2014) Association between TLR4 (+896A/G and +1196C/T) Polymorphisms and Gastric Cancer Risk: An
Updated Meta-Analysis. PLoS ONE 9(10): e109605. doi:10.1371/journal.pone.0109605
Association between TLR4 (+896A/G and +1196C/T) Polymorphisms and Gastric Cancer Risk: An Updated Meta-Analysis
Quan Zhou 0
Chenchen Wang 0
Xiaofeng Wang 0
Xiongyan Wu 0
Zhenggang Zhu 0
Bingya Liu 0
Liping Su 0
Jingwu Xie, Indiana University School of Medicine, United States of America
0 Shanghai Key Laboratory of Gastric Neoplasms, Department of Surgery, Shanghai Institute of Digestive Surgery, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine , Shanghai , People's Republic of China
Background: Toll-like receptor 4 (TLR4) is a receptor of lipopolysaccharide in the signaling transduction of gastric epithelial cell. It plays a pivotal role in activation of innate immunity and pathogen recognition and thus acts as a modulator in the development and progression of gastric cancer. Growing studies explored the association of polymorphisms in TLR4 with susceptibility to gastric cancer, but the results have remained controversial and conflicting. To investigate the effect of two selected TLR4 (+896A/G and +1196C/T) polymorphisms on gastric cancer, we performed a meta-analysis. Methods: A comprehensive search was conducted to identify all eligible case-control publications investigating the association between TLR4 polymorphisms and gastric cancer risk. Odds ratios (OR) and corresponding 95% confidence intervals (CI) were used to assess such association. Results: Up to March 26 2014, 10 published case-control studies from PubMed and EMBase were available, involving a total of 1888 gastric cancer patients and 3433 control subjects. In the overall meta-analyses, a significantly increased gastric cancer risk was detected in TLR4 +896A/G polymorphism (heterozygous model, AG vs. AA: OR = 1.67, 95% CI, 1.39-2.01; additive model, G vs. A: OR = 1.64, 95% CI, 1.37-1.95) and TLR4 +1196C/T polymorphism (heterozygous model, CT vs. CC: OR = 1.42, 95% CI, 1.11-1.81; additive model, T vs. C: OR = 1.36, 95% CI, 1.08-1.72), similar results were obtained in the subgroup analyses of Caucasian, whereas no associations were detected in any genetic models of non-Caucasian. Conclusions: The overall results suggest that TLR4 polymorphisms (+896A/G and +1196C/T) may be associated with a significantly increased gastric cancer risk in Caucasian.
Funding: This work was supported by National Natural Science Foundation of China (NSFC) - No. 81272749 [LPS] http://www.nsfc.gov.cn/; Science and
Technology Commission of Shanghai Municipality (No. 11jc1407602). [LPS] http://www.stcsm.gov.cn/; National Natural Science Foundation of China (NSFC)
No. 91229106 [BYL] http://www.nsfc.gov.cn/; Doctoral Innovation Fund Projects from Shanghai Jiao Tong University School of Medicine (BXJ201318). [QZ] http://
yjsy.shsmu.edu.cn/; Science and Technology Commission of Shanghai Municipality (No. 14DZ2272200) [ZGZ] http://www.stcsm.gov.cn/. The funders had no role
in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Gastric cancer is one of the most common malignancy and the
third leading cause of cancer death worldwide, with an estimated
952,000 new cases and 723,000 deaths occurred in 2012 .
Although surgical resection is the mainstay of treatment for gastric
cancer, overall 5-year relative survival rates for gastric cancer
patients remain utterly gloomy with approximately 60% in Asian
countries and 20% in western countries . It is well known that
gastric cancer is a devastating and multifactorial disease, which
derived from extremely complex interactions between genetic and
environmental factors . Single Nucleotide Polymorphisms
(SNPs) are the most common type of genetic variations and may
contribute to an individuals susceptibility to cancer.
Chronic inflammation is well known to play a critical role in
initiating and promoting several human cancers including gastric
cancer. TLRs activation contributes significantly to the initiation
and maintenance of inflammatory response, dysregulation of
TLRs signaling may lead to an imbalance state between
proinflammatory and anti-inflammatory cytokines, and then to an
increased susceptibility to chronic inflammatory diseases and
cancer . Accumulated evidence has suggested that SNPs located
in leucine-rich repeat(LRR) of TLRs may upregulate or
downregulate the receptor response ability to bind ligand of pathogens
which they normally recognize . Human TLR4 gene is located
on chromosome 9q32-q33 and contains four exons. It is highly
expressed on monocytes, lymphocytes and splenocytes. After
binding with LPS or other ligands and conjunction with CD14
and myeloid differential protein-2 (MD-2), TLR4 could transduce
relevant signals that promote transcription of immune-related
genes, and thus activate and magnify subsequent immune response
including NF-kB and MAPK signal pathways [6,7]. Many recent
studies have demonstrated the critical role of TLR4 in the
inflammatory-related immune response to H. Pylori infection in
the pathogenesis of gastric cancer. TLR4 polymorphisms allow H.
Pylori to elude attack from the host innate immune cell, and to
survival in gastric epithelium for a long time, leading to chronic
inflammation and causing severe gastritis, hypochlorhydria, gastric
atrophy, intestinal metaplasia and dysplasia, which are
precancerous lesions of gastric cancer .
Many SNPs in TLR4 have been detected and studied, but two
of the most typical SNPs in the fourth exon of coding sequence,
+896A/G (ID: rs4986790) and +1196C/T (ID: rs4986791), were
explored and reported extensively for the gastric cancer
susceptibility [8,13,14]. To date, several studies focused on the
association of TLR4 (+896A/G and +1196C/T) polymorphisms
with precancerous lesions, gastric cancer, across different
ethnicities , however, due to the limitations of subjects, the results
were inconsistent and controversial. For example, there were two
meta-analyses investigating the correlation between TLR4 +
896A/G polymorphism and cancer risk, but the results remained
partly conflicting [14,17]. The clinical heterogeneity derived from
included studies on diverse histological types of cancers might
affect the reliability and stability of the overall results. In addition,
the previous meta-analyses did not cover all eligible publications
related to gastric cancer and thus decreased the efficacy and
probability of detecting the authentic association between TLR4
gene polymorphisms and gastric cancer risk. To clarify and
quantify the authentic effect of TLR4 (+896A/G and +1196C/T)
polymorphisms on susceptibility to gastric cancer, we performed a
meta-analysis including all eligible case-control studies. As far as
we know, this was the most comprehensive meta-analysis
concerning this subject. All potential genetic models  and
publication bias detection methods were used in our meta-analysis,
which made the results more robust and reliable.
Materials and Methods
Identification and eligibility of relevant studies
A systematic search was conducted using the PubMed and
EMBase databases (last search was updated on March 26 2014),
with the following search details: TLR4 [All Fields] AND
(polymorphism, genetic [MeSH Terms] OR (polymorphism
[All Fields] AND genetic [All Fields]) OR genetic
polymorphism [All Fields] OR polymorphism [All Fields]) AND
(stomach neoplasms [MeSH Terms] OR (stomach [All
Fields] AND neoplasms [All Fields]) OR stomach neoplasms
[All Fields] OR (gastric [All Fields] AND cancer [All Fields])
OR gastric cancer [All Fields]). With the purpose of identifying
the extra eligible studies, the references cited in the publications or
review articles concerning this topic were manually searched too.
Our search was limited to English-language articles. The identified
studies in our meta-analysis met the following criteria: (1) studies
investigating the association of TLR4 polymorphisms (+896A/G
or +1196C/T) with gastric cancer risk; (2) case-control studies and
studies included available genotype frequencies; (3) inclusion of
comprehensive data to calculate odds ratio (OR) and 95%
confidence interval (CI); (4) publications with full-text article.
Major criteria for excluding studies were: (1) precancerous lesions
or benign tumors; (2) without control subjects; (3) duplicated
previous publications; (4) the control subjects did not meet the
Hardy-Weinberg Equilibrium (HWE). At last, 10 case-control
published studies from PubMed and EMbase were available,
including a total of 1888 gastric cancer patients and 3433 control
subjects for the TLR4 polymorphisms (+896A/G and +1196C/T).
The PRISMA checklist was available as supplementary material,
as displayed in Checklist S1.
Two investigators (QZ and CCW) performed the data
extraction independently, and then conducted consensus decision
to resolve the disagreements. All study personnel were blinded
throughout the meta-analysis. For each study, the following
information was collected: the name of first author, publication
year, country, ethnicity, design, genotyping method, number of
cases and controls, genotype and allele frequencies for cases and
controls, and HWE of controls.
The HWE was recalculated in the present meta-analysis
according to the HWE principle and formula . And a
Pvalue more than 0.05 was considered to meet HWE. Meta-analysis
for TLR4 polymorphisms was performed by using the software
Stata 12.0 (Stata Corporation, College Station, TX, USA). The
association of the TLR4 polymorphisms (+896A/G and +1196C/
T) with risk of gastric cancer was estimated by odds ratios (OR)
and 95% confidence intervals (CI). The significance of pooled OR
was measured by the Z-test, and statistical significance was
determined as a 2-sided P-value less than 0.05. We measured the
association of allele G and allele T (additive model) with gastric
cancer risk, and made comparisons with heterozygous model (AG
vs. AA) and (CT vs. CC). Heterogeneity assumption was
conducted with a x2-based Q-test. If the P-value.0.05 for
Qtest, thus demonstrating that all studies were lack of heterogeneity,
then fixed effect model was adopted to merge studies (the
MantelHaenszel method) , or else the random effect model (the
DerSimonian and Laird method) was used . Subgroup
metaanalyses according to different races (Caucasian and
nonCaucasian) have been conducted based on these genetic models.
In addition, sensitivity analysis was conducted to evaluate stability
of the results by excluding one study at a time, the pooled ORs
were recalculated to assess the altered effect of individual study on
the overall results. Furthermore, potential publication bias was
diagnosed and measured by using the Begg and Mazumdar rank
correlation test  and Funnel plots and Eggers regression test
Characteristics of eligible studies
A total of 41 studies were identified by using different
combinations of MeSH terms on PubMed and EMbase.
According to the inclusion and exclusion criteria, 10 case-control studies
that consisted of a total of 1888 gastric cancer patients and 3433
control subjects were included in this meta-analysis [11,16,2330].
Literature search strategy and included or excluded studies were
presented in Figure 1. Detailed information, such as author name,
publication year, region, ethnicity, design, genotyping method,
numbers about cases and controls were summarized in Table 1.
The publication year of eligible studies ranged from 2007 to 2014.
Two studies adopted hospital-based control, while the other eight
studies adopted population-based control. All cases diagnosed with
gastric cancer were also validated by pathological examination. All
of them adopted blood samples for genotyping. All quality scores
of selected articles were higher than 25 (moderate-high quality)
. The results of HWE test in the control population and
genotype frequencies of TLR4 +896A/G and +1196C/T
polymorphisms were recalculated and extracted from all eligible
publications, and were shown in Table 2. All the eligible studies
met the HWE (all P.0.05).
Quantitative data synthesis
The overall frequency of G allele in TLR4 +896A/G
polymorphism was 7% in cases and 5% in controls. The frequency
of the T allele in TLR4 +1196C/T polymorphism was 5% in cases
and 4% in controls. For TLR4 +896A/G polymorphism,
individuals carrying the variant AG genotype had a significantly
increased gastric cancer risk compared with the AA genotype
(heterozygous model) (AG vs. AA: OR = 1.67, 95%CI = 1.39
2.01, P = 0.000) (Figure 2A). The significance also have been
detected in the additive model for the comparison of G allele with
HB: hospital based, PB: population based, PCR-RFLP: polymerase chain reaction-restriction fragment length polymorphism.
A allele (G vs. A: OR = 1.64, 95%CI = 1.371.95, P = 0.000)
(Figure 2B). Moreover, for TLR4 +1196C/T polymorphism, an
increased gastric cancer risk was found for the comparison of CT
with CC genotype (heterozygous model) (CT vs. CC: OR = 1.42,
95%CI = 1.111.81, P = 0.005) (Figure 2C), as well as for the
comparison of T allele with C allele (additive model) (T vs. C:
OR = 1.36, 95%CI = 1.081.72, P = 0.010) (Figure 2D). Besides,
subgroup meta-analyses according to different races (Caucasian
and non-Caucasian) have been conducted based on these genetic
models. We found significantly positive correlations between the
two selected TLR4 polymorphisms and increased risks of gastric
cancer in Caucasians, but not in non-Caucasian. The significant
association of dominant model (AG+GG vs. AA: OR = 1.68,
95%CI = 1.402.02, P = 0.000 and CT+TT vs. CC: OR = 1.40,
95%CI = 1.101.78, P = 0.006) with gastric cancer risk was also
observed. In all genetic comparisons, fixed effect model
(MantelHaenszel method) was used as a result of no obvious heterogeneity
(Q-test: P.0.05, I2,50%) (Table 3). However, there was no
significant difference in homozygous model (GG vs. AA and TT
vs.CC) or recessive model (GG vs. AG+AA and TT vs. CT+TT).
There were two studies investigating the association between
TLR4 +896A/G polymorphism and H. Pylori infection in gastric
cancer patients [26,29], and one study for TLR4 +1196C/T
polymorphism . However, no significant association was
observed in the overall results, TLR4 +896A/G polymorphism
did not increase the risk of H. Pylori infection in gastric cancer
patients (Figure 3A: AG vs. AA, Figure 3B: G vs. A).
We conducted sensitivity analysis to evaluate the root of
heterogeneity. There was no heterogeneity in heterozygous,
dominant models and additive models in TLR4 +896A/G and
TLR4 +1196C/T polymorphisms. Besides, no single study
qualitatively affected the pooled OR, as demonstrated by
sensitivity analysis (Figure 4), which suggested that the results of
this meta-analysis are reliable and stable. However, there was
significant heterogeneity in homozygous and recessive model
because that the homozygous genotype GG and TT in many
studies were absent.
Publication bias within each study might not represent all
studies. We performed Beggs funnel plot and Eggers linear
regression test to assess the publication bias of all included studies.
As demonstrated in Figure 5, the funnel plots did not display any
evidence of obvious asymmetry under the heterozygous and
additive models (Figure 5A. AG vs. AA: z = 0.78, P = 0.436;
Figure 5B. G vs. A: z = 0.78, P = 0.436; Figure 5C. CT vs. CC:
z = 0.52, P = 0.602; Figure 5D. T vs. C: z = 0.730, P = 0.466).
Eggers test also suggested that there was no obvious statistical
publication bias under the heterozygous and additive models
(Figure 6A. AG vs. AA: t = 0.97, P = 0.358; Figure 6B. G vs. A:
t = 1.05, P = 0.322; Figure 6C. CT vs. CC: t = 0.71, P = 0.501;
Figure 6D. T vs. C: t = 0.97, P = 0.365).
1 7 2 0 8 5 4 # 46 69 55 8 8 8 5 4 # 47 82 55
9 6 8 4 0 0 6 6 9 6 9 4
A 2 1 2 4 4 8 3 # 4 3 5 C 3 2 1 3 4 # 4 3 5
3 8 0 4 7 5 6 3 1 7 3 5 6 1
G 1 1 4 2 4 5 6 4 2 2 1 T 1 1 1 4 9 4 9 1 1
9 2 8 0 7 0 7 4 7 3 5 5 7 8 9 3 1 4 1
2 0 2 2 7 6 5 7 7 3 0 5 2 2 1 3 6 9 4 2
A 3 1 7 3 5 5 1 6 3 2 1 C 1 3 1 1 3 6 3 2 1
Figure 2. Forest plots showing the association of the TLR4 +896A/G and +1196C/T polymorphisms with risk of gastric cancer. A. AG
vs. AA; B. G vs. A; C. CT vs. CC; D. T vs. C.
Extensive genetic and epidemiological evidence indicates that
chronic inflammation imposes great risk for the development and
progression of many kinds of cancers [32,33], especially for gastric
cancer [34,35]. TLR4 plays a pivotal role in innate immunity
defending the body against pathogenic organisms. The recognition
of TLR4 by its ligand results in a cascade reaction including the
IL-1R family activation and followed by the activation of NF-kB
, which is a key mediator of inflammation-induced gastric
cancer development [7,37]. However, the function of TLR4 at the
protein level will be impaired by SNPs in TLR4 gene,
subsequently leading to an altered susceptibility to chronic
inflammatory diseases and cancers [38,39]. The causal link
Figure 3. Forest plots showing the association of the TLR4 +896A/G polymorphism with H. Pylori infection in gastric cancer
patients. A. AG vs. AA, B. G vs. A.
between H. Pylori and gastric cancer has been confirmed. Recent
studies have revealed that SNPs within TLR4 is significantly
associated with gastric chronic-inflammation and HP infection
related mucosa lesions [12,4042]. Several SNPs within TLR4
have been identified, and the two commonest (+896A/G and +
1196C/T) of them that were founded in the fourth exon of coding
sequence affect the stability of TLR4 extracellular domain and
result in adenine-guanine (AG) and cytosine-thymine (CT)
exchanges, respectively, and thus finally cause amino acid
substitutions: glycine for aspartic at position 299 and isoleucine
for threonine at position 399 [43,44]. Wild-type TLR4 possesses a
particular area with negative charge at position 299, which is
absent in +896A/G polymorphism, and thus such polymorphism
enhances the rotational freedom and angle of the peptide bond in
the LPS/MD-2 complex binding area . Consequently, the
interaction of TLR4 with LPS may be modulated by the altered
rotation and charge, which results in the functional peculiarities of
target cells with +896A/G polymorphism . As opposed to
+896A/G polymorphism, the branched side chain is conserved in
+1196C/T polymorphism, however, the increased
three-dimenFigure 4. Sensitivity analysis for heterogeneity. A. AG vs. AA; B. G vs. A; C. CT vs. CC; D. T vs. C.
sional bulk in this region, probably preventing ligands or cofactors
from docking . Both +896A/G and +1196C/T TLR4
polymorphisms may result in the loss of docking, which cannot
be precluded by the remaining functional interactions, and it is
verified by the fact that the targeted doubly mutated TLR4
molecule permanently responds more poorly to the stimulation of
ligand than TLR4 molecules that possess either the +896A/G or
+1196C/T mutation . Individuals with TLR4 polymorphisms
possess an increased susceptibility to severe gastric inflammation,
hypochlorhydria, gastric atrophy and subsequent development of
intestinal metaplasia [8,10], which the latter two are considered as
the most critical precancerous pathological changes associated
with gastric cancer.
Although the important role of TLR4 polymorphisms in the
development of gastric cancer has been reported in recent years,
the results are inconsistent. Garza-Gonzalez et al reported that
there was no correlation between TLR4 polymorphisms and
gastric cancer in Mexican ethnicity , however, Trejo-de la et al
insisted that both SNPs (+896A/G and +1196C/T) within TLR4
had an increased susceptibility to gastro-duodenal diseases
including duodenal ulcer and gastric cancer . Other studies
suggested that only one of these two polymorphisms (either +
1196C/T or +896A/G) had association with an increased risk of
precancerous lesions and gastric cancer [4,16]. Hold et al
indicated that TLR4 +896A/G polymorphism was associated
with increased susceptibility to gastric atrophy and subsequent
gastric carcinogenesis . Recently, several studies have shown
that both +896A/G and +1196C/T SNPs were related to
increased gastric cancer risk [11,29,30], while de Oliveira et al
has shown not +1196C/T but +896A/G to be associated with
such an increased risk in a Brazilian population .
Consequently, we performed a comprehensive meta-analysis on the
correlation between the TLR4 polymorphisms (+896A/G and
+1196C/T) and gastric cancer risk. As far as we know, this was the
most comprehensive and updated meta-analysis investigating the
association between TLR4 polymorphisms and gastric cancer risk.
Because the studies involving in our meta-analysis completely met
all the screening criteria, the results from these pooled studies were
more powerful than those from single study. After searching the
PubMed and EMbase, a total of 10 case-control studies were
available including 1888 gastric cancer patients and 3433 control
subjects from 2007 to 2014. Consistent with the conclusions
resulted from the mentioned studies, our results demonstrate that
both +896A/G and +1196C/T TLR4 polymorphisms are
associated with a significantly increased gastric cancer, especially
for genotype model (heterozygous: AG vs. AA, dominant: GG+
AG vs. AA, heterozygous: CT vs. CC, dominant: CT+TT vs. CC)
and additive model (G vs. A and T vs. C). Therefore, these two
Figure 5. Beggs funnel plots for publication bias test. A. AG vs. AA; B. G vs. A; C. CT vs. CC; D. T vs. C.
polymorphisms should be regarded as the most significant
polymorphisms in TLR4. In the overall +896A/G and +1196C/
T meta-analyses, we demonstrated that the minor alleles could
obviously increase the risk of gastric cancer in comparison with
major alleles, showing that these two genetic variants may critically
modify the susceptibility to gastric cancer. In the subgroup
metaanalyses, we found significantly positive correlations between the
two selected TLR4 polymorphisms and increased risks of gastric
cancer in Caucasians, but not in non-Caucasian. The discrepancy
between the two races may be attributed to the differences of life
styles and diverse environmental exposure factors of the different
However, there are several limitations of the current
metaanalysis, which must be taken into consideration. Because the
homozygous genotypes of TLR4 gene (GG and TT) were almost
completely absent in the population studied, homozygous and
recessive models were absent in the present study. To reconfirm
this result, more cases about comprehensive population (Western
countries and Asian countries) should be included in the study on
the association of TLR4 SNPs with gastric cancer. In addition,
articles in other languages (not English) were excluded, which may
deviate the results. Besides, subgroup analysis according to gastric
cancer site (cardia and noncardia) and histological type, and risk
factor analysis for different precancerous lesions according to its
type, could provide us more valuable information, but the sample
size and individual original data limitations hinder a statistically
significant analysis. Finally, TLRs induce the expression of
proinflammatory genes on gastric mucosa, and the interactions
between environmental carcinogens (biologic, chemical and
physical stimulations) and host cells, that could be used to
elucidate the mechanism by which TLR4 +896A/G and +1196C/
T polymorphisms increase risk of developing gastric cancer. More
original data need to be obtained to interpret the
geneenvironment interactions and subsequent gastric carcinogenesis.
In conclusion, this meta-analysis demonstrates that TLR4
+896A/G and +1196C/T polymorphisms probably increase the
susceptibility to gastric cancer mainly in Caucasians, while the
susceptibility to gastric cancer in Chinese and other Asian
population need to be proved in future large scale studies.
Although genome-wide association studies (GWAS) are important
procedures for the discovery of genetic variations and the
reliability of meta-analysis, there are no available previous GWAS
on this subject, thus, we have performed sensitivity analysis and
publication bias test to avoid such potential discrepancy in this
meta-analysis, which suggests no obvious selection bias and
confirms the reliability and stability of our results. Since gastric
cancer is a multifactorial and multistep disease, it is important to
perform well-design and large scale studies, including
comprehensive individual data, homogenous patients and underlying source
population based controls, standardized genotyping methods to
thoroughly reveal the association of TLR4 polymorphisms with
gastric cancer risk.
Figure 6. Eggers linear regression plots for publication bias test. A. AG vs. AA; B. G vs. A; C. CT vs. CC; D. T vs. C.
PRISMA meta-analysis checklist.
We thank all the people who helped in this study.
Conceived and designed the experiments: LPS BYL. Performed the
experiments: QZ CCW. Analyzed the data: QZ CCW XFW XYW.
Contributed reagents/materials/analysis tools: QZ CCW XFW XYW.
Wrote the paper: QZ LPS. Reviewed the manuscript: ZGZ BYL.
1. WHO: World Health Organization: stomach cancer (2014) estimated incidence, mortality and prevalence worldwide in 2012 . Available: http://globocan.iarc. fr/ Pages/fact_sheets_cancer.aspx. Accessed: 2014 Mar 26 .
2. Kamangar F , Dores GM , Anderson WF ( 2006 ) Patterns of cancer incidence, mortality, and prevalence across five continents: defining priorities to reduce cancer disparities in different geographic regions of the world . J Clin Oncol 24 : 2137 - 2150 .
3. Pharoah PD , Dunning AM , Ponder BA , Easton DF ( 2004 ) Association studies for finding cancer-susceptibility genetic variants . Nat Rev Cancer 4 : 850 - 860 .
4. Achyut BR , Ghoshal UC , Moorchung N , Mittal B ( 2007 ) Association of Toll-like receptor-4 (Asp299Gly and Thr399Ileu) gene polymorphisms with gastritis and precancerous lesions . Hum Immunol 68 : 901 - 907 .
5. Bell JK , Mullen GE , Leifer CA , Mazzoni A , Davies DR , et al. ( 2003 ) Leucinerich repeats and pathogen recognition in Toll-like receptors . Trends Immunol 24 : 528 - 533 .
6. Takeda K , Akira S ( 2005 ) Toll-like receptors in innate immunity . Int Immunol 17 : 1 - 14 .
7. He C , Chen M , Liu J , Yuan Y ( 2014 ) Host genetic factors respond to pathogenic step-specific virulence factors of Helicobacter pylori in gastric carcinogenesis . Mutat Res 759C : 14 - 26 .
8. El-Omar EM , Ng MT , Hold GL ( 2008 ) Polymorphisms in Toll-like receptor genes and risk of cancer . Oncogene 27 : 244 - 252 .
9. Hishida A , Matsuo K , Goto Y , Hamajima N ( 2010 ) Genetic predisposition to Helicobacter pylori-induced gastric precancerous conditions . World J Gastrointest Oncol 2 : 369 - 379 .
10. Fan YF , Wu YM , Liu H , Yu Y , Jiang YY , et al. ( 2014 ) TLR4 polymorphisms associated with developing gastric pre-cancer lesions in a Chinese Han population . Hum Immunol 75 : 176 - 181 .
11. Companioni O , Bonet C , Munoz X , Weiderpass E , Panico S , et al. ( 2014 ) Polymorphisms of Helicobacter pylori signaling pathway genes and gastric cancer risk in the European Prospective Investigation into Cancer-Eurgast cohort . Int J Cancer 134 : 92 - 101 .
12. Kato I , Canzian F , Plummer M , Franceschi S , van Doorn LJ , et al. ( 2007 ) Polymorphisms in genes related to bacterial lipopolysaccharide/peptidoglycan signaling and gastric precancerous lesions in a population at high risk for gastric cancer . Dig Dis Sci 52 : 254 - 261 .
13. Zou TH , Wang ZH , Fang JY ( 2013 ) Positive association between Toll-like receptor 4 gene +896A/G polymorphism and susceptibility to gastric carcinogenesis: a meta-analysis . Tumour Biol 34 : 2441 - 2450 .
14. Zhang K , Zhou B , Wang Y , Rao L , Zhang L ( 2013 ) The TLR4 gene polymorphisms and susceptibility to cancer: a systematic review and metaanalysis . Eur J Cancer 49 : 946 - 954 .
15. Chen J , Hu S , Liang S , Chen Q , Yang Q , et al. ( 2013 ) Associations between the four toll-like receptor polymorphisms and the risk of gastric cancer: a metaanalysis . Cancer Biother Radiopharm 28 : 674 - 681 .
16. Santini D , Angeletti S , Ruzzo A , Dicuonzo G , Galluzzo S , et al. ( 2008 ) Toll-like receptor 4 Asp299Gly and Thr399Ile polymorphisms in gastric cancer of intestinal and diffuse histotypes . Clin Exp Immunol 154 : 360 - 364 .
17. Jing JJ , Li M , Yuan Y ( 2012 ) Toll-like receptor 4 Asp299Gly and Thr399Ile polymorphisms in cancer: a meta-analysis . Gene 499 : 237 - 242 .
18. Zhu B , Wu X , Zhi X , Liu L , Zheng Q , et al. ( 2014 ) Methylenetetrahydrofolate Reductase C677T Polymorphism and Type 2 Diabetes Mellitus in Chinese Population: A Meta-Analysis of 29 Case-Control Studies . PLoS One 9 : e102443 .
19. Ward R , Carroll RJ ( 2014 ) Testing Hardy-Weinberg equilibrium with a simple root-mean-square statistic . Biostatistics 15 : 74 - 86 .
20. Mantel N , Haenszel W ( 1959 ) Statistical aspects of the analysis of data from retrospective studies of disease . J Natl Cancer Inst 22 : 719 - 748 .
21. DerSimonian R , Laird N ( 1986 ) Meta-analysis in clinical trials . Control Clin Trials 7 : 177 - 188 .
22. Begg CB , Mazumdar M ( 1994 ) Operating characteristics of a rank correlation test for publication bias . Biometrics 50 : 1088 - 1101 .
23. Egger M , Davey Smith G , Schneider M , Minder C ( 1997 ) Bias in meta-analysis detected by a simple, graphical test . BMJ 315 : 629 - 634 .
24. Trejo-de la OA , Torres J , Perez-Rodriguez M , Camorlinga-Ponce M , Luna LF , et al. ( 2008 ) TLR4 single-nucleotide polymorphisms alter mucosal cytokine and chemokine patterns in Mexican patients with Helicobacter pylori-associated gastroduodenal diseases . Clin Immunol 129 : 333 - 340 .
25. de Oliveira JG , Silva AE ( 2012 ) Polymorphisms of the TLR2 and TLR4 genes are associated with risk of gastric cancer in a Brazilian population . World J Gastroenterol 18 : 1235 - 1242 .
26. Hold GL , Rabkin CS , Chow WH , Smith MG , Gammon MD , et al. ( 2007 ) A functional polymorphism of toll-like receptor 4 gene increases risk of gastric carcinoma and its precursors . Gastroenterology 132 : 905 - 912 .
27. Garza-Gonzalez E , Bosques-Padilla FJ , Mendoza-Ibarra SI , Flores-Gutierrez JP , Maldonado-Garza HJ , et al. ( 2007 ) Assessment of the toll-like receptor 4 Asp299Gly, Thr399Ile and interleukin-8 -251 polymorphisms in the risk for the development of distal gastric cancer . BMC Cancer 7 : 70 .
28. de Oliveira JG , Rossi AF , Nizato DM , Miyasaki K , Silva AE ( 2013 ) Profiles of gene polymorphisms in cytokines and Toll-like receptors with higher risk for gastric cancer . Dig Dis Sci 58 : 978 - 988 .
29. Qadri Q , Rasool R , Afroze D , Naqash S , Gulzar GM , et al. ( 2013 ) Study of TLR4 and IL-8 Gene Polymorphisms in H.pylori-Induced Inflammation in Gastric Cancer in an Ethnic Kashmiri Population . Immunol Invest 43 : 324 - 336 .
30. Kutikhin AG , Yuzhalin AE , Volkov AN , Zhivotovskiy AS , Brusina EB ( 2014 ) Correlation between genetic polymorphisms within IL-1B and TLR4 genes and cancer risk in a Russian population: a case-control study . Tumour Biol 35 : 4821 - 4830 .
31. da Costa BR , Cevallos M , Altman DG , Rutjes AW , Egger M ( 2011 ) Uses and misuses of the STROBE statement: bibliographic study . BMJ Open 1 : e000048 .
32. Cole SW ( 2009 ) Chronic inflammation and breast cancer recurrence . J Clin Oncol 27 : 3418 - 3419 .
33. Kazma R , Mefford JA , Cheng I , Plummer SJ , Levin AM , et al. ( 2012 ) Association of the innate immunity and inflammation pathway with advanced prostate cancer risk . PLoS One 7 : e51680 .
34. Bornschein J , Malfertheiner P ( 2011 ) Gastric carcinogenesis . Langenbecks Arch Surg 396 : 729 - 742 .
35. Wang F , Meng W , Wang B , Qiao L ( 2014 ) Helicobacter pylori-induced gastric inflammation and gastric cancer . Cancer Lett 345 : 196 - 202 .
36. Aderem A , Ulevitch RJ ( 2000 ) Toll-like receptors in the induction of the innate immune response . Nature 406 : 782 - 787 .
37. Huang B , Zhao J , Li H , He KL , Chen Y , et al. ( 2005 ) Toll-like receptors on tumor cells facilitate evasion of immune surveillance . Cancer Res 65 : 5009 - 5014 .
38. Armant MA , Fenton MJ ( 2002 ) Toll-like receptors: a family of patternrecognition receptors in mammals . Genome Biol 3 : REVIEWS3011 .
39. Liew FY , Xu D , Brint EK , O'Neill LA ( 2005 ) Negative regulation of toll-like receptor-mediated immune responses . Nat Rev Immunol 5 : 446 - 458 .
40. Schmausser B , Andrulis M , Endrich S , Lee SK , Josenhans C , et al. ( 2004 ) Expression and subcellular distribution of toll-like receptors TLR4, TLR5 and TLR9 on the gastric epithelium in Helicobacter pylori infection . Clin Exp Immunol 136 : 521 - 526 .
41. Hamajima N ( 2003 ) Persistent Helicobacter pylori infection and genetic polymorphisms of the host . Nagoya J Med Sci 66 : 103 - 117 .
42. Bagheri N , Azadegan-Dehkordi F , Sanei H , Taghikhani A , Rahimian G , et al. ( 2014 ) Associations of a TLR4 single-nucleotide polymorphism with H. pylori associated gastric diseases in iranian patients . Clin Res Hepatol Gastroenterol 38 : 366 - 371 .
43. Arbour NC , Lorenz E , Schutte BC , Zabner J , Kline JN , et al. ( 2000 ) TLR4 mutations are associated with endotoxin hyporesponsiveness in humans . Nat Genet 25 : 187 - 191 .
44. Mockenhaupt FP , Cramer JP , Hamann L , Stegemann MS , Eckert J , et al. ( 2006 ) Toll-like receptor (TLR) polymorphisms in African children: common TLR-4 variants predispose to severe malaria . J Commun Dis 38 : 230 - 245 .
45. Rallabhandi P , Bell J , Boukhvalova MS , Medvedev A , Lorenz E , et al. ( 2006 ) Analysis of TLR4 polymorphic variants: new insights into TLR4/MD-2/CD14 stoichiometry, structure, and signaling . J Immunol 177 : 322 - 332 .
46. Ferwerda B , McCall MB , Verheijen K , Kullberg BJ , van der Ven AJ , et al. ( 2008 ) Functional consequences of toll-like receptor 4 polymorphisms . Mol Med 14 : 346 - 352 .