Abstract
Objectives: Published data on the association between Interleukin-8-251A/T polymorphism and gastric cancer (GC) risk are inconclusive. Thus, we conducted a meta-analysis to evaluate the relationship between cyclin D1 G870A polymorphism and GC risk. Methods: We searched PubMed, EMBASE, Web of science and the Cochrane Library up to July 12, 2015 for relevant studies. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to estimate the strength of associations. Results: Twenty-six studies published from 2004 to 2015, with a total of 5286 cases and 8000 controls, were included in this meta-analysis. The pooled results showed that there was significant association between Interleukin-8-251A/T polymorphism and GC risk in any genetic model. In the subgroup analysis by ethnicity, the effects remained in Asians. However, no genetic models reached statistical association in Europeans. The subgroup analysis stratified by Source of controls showed an increased breast cancer risk in hospital-based (HB) studies in any genetic model except recessive model. However, there was no association in any genetic model in population based (PB) studies. When stratifying by Genotyping method, we found statistical association in Non-RFLP (restriction fragment length polymorphism) in any genetic model except heterozygote comparison, the effect was remain in PCR-RFLP in dominant model and heterozygote comparison. Conclusions: This meta-analysis suggests that Interleukin-8-251A/T polymorphism is a risk factor for susceptibility to GC in overall population, especially in Asians, in hospital populations and in Non-RFLP. While, there was no association in Europeans and in general population. Further large scale multicenter epidemiological studies are warranted to confirm this finding.
Keywords: Interleukin-8-251A/T, polymorphism, gastric cancer, susceptibility, meta-analysis
Introduction
Gastric cancer (GC) is one of the most common malignant tumors and the third leading cause of cancer-related death in the word, the 5-year survival rate is low, especially for advanced GC [1,2]. In the majority of developing countries, the incidence of GC is constantly increasing, as well as mortality [3,4]. For most GCs are diagnosed to be advanced stages, early detection seems particularly important [5]. While, the determination of the association between Interleukin-8-251A/T polymorphism and GC risk provides us a promising approach to achieve this goal.
Interleukin-8 is an important member of the chemokine superfamily, which belongs to the CXC chemokine family. Under the stimulation of a variety of factors (such as lipopolysaccharide, IL.1, etc.), many cells can produce IL-8, such as monocytes, endothelial cells and tumor cells [6,7]. In recent years, the expression of IL-8 in tumor cells was significantly increased. It is found that IL-8 can induce the migration and proliferation of endothelial cells to mediate tumor angiogenesis, which can promote tumor [8-10]. Human IL-8 gene is located on fourth chromosome, composed of four exons, three introns, and a proximal promoter region. In the promoter region of IL-8, there is a genetic polymorphism in -251T, which has been reported to be closely associated with altered expression levels of IL-8 through gene transcription regulation [11].
Previous functional studies have reported the association between Interleukin-8-251A/T polymorphism and GC risk, but the results remain inconclusive [12-37]. To clarify the role of Interleukin-8-251A/T polymorphism in GC risk, four meta-analysis on the associations between Interleukin-8-251A/T polymorphism and cancers [38-41]. However, number of their studies included in their meta-analysis about GC is small, and GC is just a small part of their study. In the subgroup of their analyses the sample size is extremely small, and some just no subgroup. Therefore, we decided to carry out a meta-analysis on all eligible case-control studies to make a more precise estimation of the association. Furthermore, we conducted the subgroup analysis by stratification according to the ethnicity, source of controls and genotyping method.
Materials and methods
Literature searching strategy
We searched PubMed, EMBASE, Web of science, the Cochrane Library for relevant studies published before July 12, 2015. The following keywords were used: interleukin*/IL*, variant/genotype/polymorphism/SNP, Gastric/stomach/cardia, cancer/carcinom*/neoplasm*/tumor and the combined phrases for all genetic studies on the association between the Interleukin-8-251A/T polymorphism and GC risk. The reference lists of all articles were also manually screened for potential studies. Abstracts and citations were screened independently by two authors, all the agreed articles need a second screen for full-text reports. The searching was done without restriction on language.
Selection and exclusion criteria
Inclusion criteria: A study was included in this meta-analysis if it meets the following criteria: i) independent case-control studies for humans; ii) the study evaluated the association between Interleukin-8-251A/T polymorphism and GC risk; iii) has available genotype frequencies in cancer cases and control subjects for risk estimate. We excluded comments, editorials, systematic reviews or studies lacking sufficient data. If the publications were duplicated or shared in more than one study, the most recent publications were included. All identified studies were screened by two investigators independently. What’s more, there was no limitation for publication language.
Data extraction and synthesis
We used endnote bibliographic software to construct an electronic library of citations identified in the literature search. All the PubMed, EMBASE, Web of science and the Cochrane Library searches were performed using Endnote; duplicates were found automatically by endnote and deleted manually. All data extraction were checked and calculated twice according to the inclusion criteria listed above by two independent investigators. Data extracted from the included studies were as follows: First author, year of publication, country, ethnicity, Source of controls, Genotyping method, number of cases and controls and evidence of HWE in controls. A third reviewer would participate if some disagreements were emerged, and a final decision was made by the majority of the votes.
Statistical analysis
All statistical analyses were performed using STATA version 11.0 software (StataCorp LP, College Station, TX) and Review Manage version 5.2.0 (The Cochrane Collaboration, 2012). Hardy-Weinberg equilibrium (HWE) was assessed by χ2 test in the control group of each study [42]. The strength of associations between the Interleukin-8-251A/T polymorphism and GC risk were measured by odds ratio (ORs) with 95% confidence interval (CIs). Z test was used to assess the significance of the ORs, I2 and Q statistics was used to determine the statistical heterogeneity among studies. A random-effect model was used if P value of heterogeneity tests was no more than 0.1 (P≤0.1), otherwise, a fixed-effect model was selected [42,43]. Sensitivity analyses were performed to assess the stability of the results. We used Begg’s funnel plot and Egger’s test to evaluate the publication bias [44,45]. The strength of the association was estimated in the allele model, the dominant model, the recessive model, the homozygous genetic model, and the heterozygous genetic model, respectively. P<0.05 was considered statistically significant. We performed subgroup according to Ethnicity, Source of controls, Genotyping method.
Results
Characteristics of included studies
Detailed search procedures are summarized in Figure 1. A total of 2499 references were preliminarily identified at first based on our selection strategy. We also identified 1 paper through other source. After excluding duplicate articles, we reviewed titles and abstracts of all identified studies to exclude those that were clearly irrelevant. Next, the full texts of the remaining articles were examined according to the inclusion and exclusion criteria. Finally, 26 studies [12-37] on Interleukin-8-251A/T polymorphism and GC risk were finally identified in this meta-analysis, including 5286 cases and 8000 controls. The characteristics of the included studies are listed in Table 1. The 26 case-control studies were published between 2004 and 2015, among them, 9 studies were performed in European and 17 in Asians. All studies were case-controlled. 13 studies were hospital-based and 13 were population-based studies.
Figure 1.
Flow chart of studies selection in this meta-analysis.
Table 1.
Characteristics of the studies included in the meta-analysis
First author | Year | Country | Ethnicity | Source of controls | Genotyping method | Number (case/control) | HWE | Quality assessment score | Published language |
---|---|---|---|---|---|---|---|---|---|
Bo [37] | 2010 | China | Asian | HB | PCR-RFLP | 208/190 | 0.389403209 | 7 | English |
Canedo [36] | 2008 | Portugal | European | PB | Taq Man-PCR | 333/693 | 0.459719109 | 8 | English |
Crusius [35] | 2008 | Caucasia | European | PB | Real-time | 236/1139 | 0.705567725 | 8 | English |
de Oliveira [34] | 2015 | Brazil | European | HB | PCR-RFLP | 207/240 | 0.059480986 | 7 | English |
Felipe [33] | 2012 | Brazil | European | PB | PCR-RFLP | 104/196 | 0.065528611 | 8 | English |
Garza-Gonzalez [32] | 2007 | Mexico | European | HB | ARMS-PCR | 78/189 | 0.538816094 | 7 | English |
Kamali-Sarvestani [31] | 2006 | Iran | Asian | HB | ASO-PCR | 19/153 | 0.797575578 | 7 | English |
Kamangar [30] | 2006 | Finland | European | PB | TaqMan-PCR | 112/207 | 0.054934096 | 8 | English |
Kang [29] | 2009 | Korea | Asian | PB | PCR-RFLP | 334/322 | 0.22569954 | 8 | English |
Ko [28] | 2009 | Korea | Asian | PB | Snapshot | 81/308 | 0.155354832 | 8 | English |
Lee [27] | 2005 | Taiwan | Asian | HB | PCR-RFLP | 470/308 | 0.14303682 | 7 | English |
Liu [12] | 2009 | China | Asian | HB | Taq Man-PCR | 138/137 | 0.145093518 | 7 | Chinese |
Lu [26] | 2005 | China | Asian | PB | PCR-DHPLC | 250/300 | 0.515848398 | 8 | English |
Ohyauchi [25] | 2005 | Japan | Asian | HB | Direct | 212/346 | 0.549317592 | 7 | English |
Pan [24] | 2014 | China | Asian | HB | SBE | 308/308 | 0.715713139 | 7 | English |
Qadri [23] | 2014 | India | Asian | PB | PCR-CTPP | 130/200 | 0.066109789 | 8 | English |
Ramis [22] | 2015 | Brazil | European | PB | PCR-RFLP | 9/38 | 0.691258974 | 8 | English |
Savage [21] | 2004 | China | Asian | PB | SBE | 88/429 | 0.884813104 | 8 | English |
Savage [20] | 2006 | Poland | European | PB | Taqman or MGB Eclipse | 287/428 | 0.391465014 | 8 | English |
Shirai [19] | 2006 | Japan | Asian | HB | PCR-RFLP | 181/468 | 0.830460367 | 7 | English |
Song [18] | 2009 | China | Asian | HB | PCR-RFLP | 125/140 | 0.720157181 | 7 | English |
Taguchi [17] | 2005 | Japan | Asian | HB | PCR-RFLP | 396/252 | 0.994013656 | 7 | English |
Vinagre [16] | 2011 | Brazil | European | HB | PCR-RFLP | 102/103 | 0.150502334 | 7 | English |
Ye [15] | 2009 | Korea | Asian | HB | PCR-RFLP | 153/206 | 0.552934095 | 7 | English |
Zeng [14] | 2005 | China | Asian | PB | PCR-RDB | 206/196 | 0.02187681 | 8 | Chinese |
Zhang [13] | 2010 | China | Asian | PB | PCR-RFLP | 519/504 | 0.75413968 | 8 | English |
HWE: Hardy-Weinberg equilibrium; PB: population based; HB: hospital-based; PCR: polymerase chain reaction; RFLP: restriction fragment length polymorphism; SBE, single base extension; PCR-RDB, polymerase chain reaction-reverse dot blot. DHPLC: PCR-based denaturing high-performance liquid chromatography; Direct: Direct sequence analysis of polymerase chain reaction; ASO: oligonucleotide allele specific polymerase chain reaction; MGB Eclipse: MGB Eclipse Assay polymerase chain reaction method; ARMS: Amplification refractory mutation system polymerase chain reaction; Snapshot: the Snapshot assay which provides detection of certain SNPs. CTPP: confronting two-pair primers. The quality of studies included in this meta-analysis was assessed using Newcastle-Ottawa scale, which graded the quality of a study from 0 to 10 points. Articles exceeding 6 points were considered as high quality.
Meta-analysis results
Table 2 shows the interleukin-8-251A/T polymorphisms genotype distribution and allele frequency in cases and controls. The main results of this meta-analysis were listed in Table 3. There were 26 studies with 5286 cases and 8000 controls for Interleukin-8-251A/T polymorphism. As shown in Table 3, The pooled results showed that there was significant association between Interleukin-8-251A/T polymorphism and GC risk in any genetic model: Allele model (A vs. T: OR=1.16, 95% CI=1.05-1.27, P=0.002), dominant model (AA + AT vs. TT: OR=1.22, 95% CI=1.07-1.39, P=0.003) recessive model (AA vs. AT + TT: OR=1.20, 95% CI=1.01-1.41, P=0.03) homozygous genetic model (AA vs. TT: OR=1.31, 95% CI=1.08-1.59, P=0.006) heterozygote comparison (AT vs. TT: OR=1.19, 95% CI=1.04-1.35, P=0.01). In the subgroup analysis by ethnicity, the effects remained in Asians (A vs. T: OR=1.23, 95% CI=1.10-1.37, P=0.0002; AA + AT vs. TT: OR=1.30, 95% CI=1.13-1.49, P=0.0002; AA vs. AT + TT: OR=1.33, 95% CI=1.07-1.64, P=0.009; AA vs. TT: OR=1.49, 95% CI=1.18-1.87, P=0.0009; AT vs. TT: OR=1.25, 95% CI=1.09-1.43, P=0.001). However, no genetic models reached statistical association in Europeans (Table 3).
Table 2.
Interleukin-8-251A/T polymorphisms genotype distribution and allele frequency in cases and controls
First author | Genotype (N) | Allele frequency (N) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||
Case | Control | Case | Control | |||||||||
| ||||||||||||
Total | AA | AT | TT | Total | AA | AT | TT | A | T | A | T | |
Bo | 208 | 36 | 108 | 64 | 190 | 26 | 96 | 68 | 180 | 236 | 148 | 232 |
Canedo | 333 | 53 | 169 | 111 | 693 | 137 | 353 | 203 | 275 | 391 | 627 | 759 |
Crusius | 236 | 48 | 113 | 75 | 1139 | 250 | 574 | 315 | 209 | 263 | 1074 | 1204 |
de Oliveira | 207 | 47 | 98 | 62 | 240 | 45 | 134 | 61 | 192 | 222 | 224 | 256 |
Felipe | 104 | 15 | 58 | 31 | 196 | 52 | 85 | 59 | 88 | 120 | 189 | 203 |
Garza-Gonzalez | 78 | 16 | 47 | 15 | 189 | 33 | 87 | 69 | 79 | 77 | 153 | 225 |
Kamali-Sarvestani | 19 | 9 | 6 | 4 | 153 | 22 | 74 | 57 | 24 | 14 | 118 | 188 |
Kamangar | 112 | 14 | 56 | 42 | 207 | 24 | 111 | 72 | 84 | 140 | 159 | 255 |
Kang | 334 | 49 | 159 | 126 | 322 | 27 | 148 | 147 | 257 | 411 | 202 | 442 |
Ko | 81 | 12 | 35 | 34 | 308 | 27 | 146 | 135 | 59 | 103 | 200 | 416 |
Lee | 470 | 59 | 213 | 198 | 308 | 62 | 138 | 108 | 331 | 609 | 262 | 354 |
Liu | 138 | 23 | 89 | 26 | 137 | 15 | 72 | 50 | 135 | 141 | 102 | 172 |
Lu | 250 | 54 | 102 | 94 | 300 | 37 | 144 | 119 | 210 | 290 | 218 | 382 |
Ohyauchi | 212 | 13 | 106 | 93 | 346 | 20 | 118 | 208 | 132 | 292 | 158 | 534 |
Pan | 308 | 48 | 168 | 92 | 308 | 59 | 148 | 101 | 264 | 352 | 266 | 350 |
Qadri | 130 | 12 | 68 | 50 | 200 | 12 | 94 | 94 | 92 | 168 | 118 | 282 |
Ramis | 9 | 4 | 1 | 4 | 38 | 7 | 20 | 11 | 9 | 9 | 34 | 42 |
Savage | 88 | 23 | 39 | 26 | 429 | 75 | 207 | 147 | 85 | 91 | 357 | 501 |
Savage | 287 | 76 | 140 | 71 | 428 | 117 | 205 | 106 | 292 | 282 | 439 | 417 |
Shirai | 181 | 20 | 78 | 83 | 468 | 49 | 208 | 211 | 118 | 244 | 306 | 630 |
Song | 125 | 20 | 72 | 33 | 140 | 23 | 70 | 47 | 112 | 138 | 116 | 164 |
Taguchi | 396 | 44 | 191 | 161 | 252 | 22 | 105 | 125 | 279 | 513 | 149 | 355 |
Vinagre | 102 | 25 | 56 | 21 | 103 | 19 | 42 | 42 | 106 | 98 | 80 | 126 |
Ye | 153 | 17 | 82 | 54 | 206 | 23 | 86 | 97 | 116 | 190 | 132 | 280 |
Zeng | 206 | 59 | 110 | 37 | 196 | 39 | 114 | 43 | 228 | 184 | 192 | 200 |
Zhang | 519 | 128 | 261 | 130 | 504 | 93 | 251 | 160 | 517 | 521 | 437 | 571 |
Table 3.
Meta-analysis results
Subgroup | OR | 95% CI | P value | Heterogeneity | Effects model | ||
---|---|---|---|---|---|---|---|
| |||||||
I2 | P value | ||||||
Allele model A vs. T | |||||||
Overall | 1.16 | 1.05-1.27 | 0.002 | 66% | P<0.00001 | R | |
Ethnicity | European | 1.01 | 0.87-1.17 | 0.90 | 54% | 0.03 | R |
Asian | 1.23 | 1.10-1.37 | 0.0002 | 61% | 0.0005 | R | |
Source of controls | PB | 1.10 | 0.98-1.24 | 0.09 | 58% | 0.004 | R |
HB | 1.23 | 1.05-1.43 | 0.01 | 72% | P<0.0001 | R | |
Genotyping method | PCR-RFLP | 1.13 | 0.98-1.30 | 0.10 | 68% | 0.0003 | R |
Non-RFLP | 1.18 | 1.04-1.35 | 0.01 | 66% | 0.0002 | R | |
Dominant model AA + AT vs. TT | |||||||
Overall | 1.22 | 1.07-1.39 | 0.003 | 61% | P<0.0001 | R | |
Ethnicity | European | 1.05 | 0.81-1.35 | 0.71 | 64% | 0.005 | R |
Asian | 1.30 | 1.13-1.49 | 0.0002 | 49% | 0.01 | R | |
Source of controls | PB | 1.09 | 0.98-1.21 | 0.13 | 27% | 0.17 | F |
HB | 1.40 | 1.12-1.76 | 0.004 | 73% | P<0.0001 | R | |
Genotyping method | PCR-RFLP | 1.20 | 1.00-1.46 | 0.06 | 62% | 0.002 | R |
Non-RFLP | 1.23 | 1.02-1.49 | 0.03 | 63% | 0.0007 | R | |
Recessive model AA vs. AT + TT | |||||||
Overall | 1.20 | 1.01-1.41 | 0.03 | 60% | P<0.0001 | R | |
Ethnicity | European | 0.94 | 0.80-1.10 | 0.43 | 38% | 0.12 | F |
Asian | 1.33 | 1.07-1.64 | 0.009 | 61% | 0.0005 | R | |
Source of controls | PB | 1.25 | 0.99-1.58 | 0.06 | 65% | 0.0005 | R |
HB | 1.14 | 0.90-1.44 | 0.29 | 54% | 0.01 | R | |
Genotyping method | PCR-RFLP | 1.12 | 0.87-1.45 | 0.39 | 63% | 0.002 | R |
Non-RFLP | 1.27 | 1.01-1.58 | 0.04 | 60% | 0.002 | R | |
Homozygous genetic model AA vs. TT | |||||||
Overall | 1.31 | 1.08-1.59 | 0.006 | 63% | P<0.00001 | R | |
Ethnicity | European | 1.01 | 0.76-1.34 | 0.97 | 50% | 0.04 | R |
Asian | 1.49 | 1.18-1.87 | 0.0009 | 60% | 0.0008 | R | |
Source of controls | PB | 1.27 | 0.98-1.64 | 0.07 | 63% | 0.001 | R |
HB | 1.38 | 1.02-1.88 | 0.04 | 66% | 0.0005 | R | |
Genotyping method | PCR-RFLP | 1.24 | 0.91-1.67 | 0.17 | 67% | 0.0005 | R |
Non-RFLP | 1.38 | 1.06-1.80 | 0.02 | 62% | 0.001 | R | |
Heterozygote comparison AT vs. TT | |||||||
Overall | 1.19 | 1.04-1.35 | 0.01 | 57% | 0.0002 | R | |
Ethnicity | European | 1.07 | 0.81-1.42 | 0.63 | 67% | 0.002 | R |
Asian | 1.25 | 1.09-1.43 | 0.001 | 41% | 0.04 | R | |
Source of controls | PB | 1.04 | 0.93-1.16 | 0.54 | 5% | 0.39 | F |
HB | 1.39 | 1.11-1.74 | 0.004 | 68% | 0.0002 | R | |
Genotyping method | PCR-RFLP | 1.20 | 1.00-1.45 | 0.05 | 55% | 0.01 | R |
Non-RFLP | 1.18 | 0.97-1.42 | 0.09 | 60% | 0.002 | R |
F-fixed effects model; R-random effects model.
The subgroup analysis stratified by Source of controls showed an increased breast cancer risk in hospital-based (HB) studies in any genetic model except recessive model (A vs. T: OR=1.23, 95% CI=1.05-1.43, P=0.01; AA + AT vs. TT: OR=1.40, 95% CI=1.12-1.76, P=0.004; AA vs. TT: OR=1.38, 95% CI=1.02-1.88, P=0.04; AT vs. TT: OR=1.39, 95% CI=1.11-1.74, P=0.004). However, there was no association in any genetic model in population based (PB) studies (Table 3).
When stratifying by Genotyping method, we found statistical association in Non-RFLP (restriction fragment length polymorphism) in any genetic model except heterozygote comparison (A vs. T: OR=1.18, 95% CI=1.04-1.35, P=0.01; AA + AT vs. TT: OR=1.23, 95% CI=1.02-1.49, P=0.03; AA vs. AT + TT: OR=1.27, 95% CI=1.01-1.58, P=0.04; AA vs. TT: OR=1.38, 95% CI=1.06-1.80, P=0.02), the effect was remain in PCR-RFLP in dominant model and heterozygote comparison (AA + AT vs. TT: OR=1.20, 95% CI=1.00-1.46, P=0.06; AT vs. TT: OR=1.20, 95% CI=1.00-1.45, P=0.05).
Sensitivity analyses
As shown in Table 1, all the studies conformed to he balance of Hardy-Weinberg equilibrium (HWE) in controls except Zeng’s (P<0.05), however, after performing the sensitivity analyses, The overall results did not show quantitative changes when excluding any study, suggesting the stability and reliability of this meta-analysis.
Detection for heterogeneity
Statistically significant heterogeneity was observed between trials of the following analyses using Q statistic: allele model (A vs. T: P<0.00001, I2=66%), the dominant model (AA + AT vs. TT: P<0.0001, I2=61%), the recessive model (AA vs. AT + TT: P<0.0001, I2=60%), the homozygous genetic model (AA vs. TT: P<0.00001, I2=63%), and the heterozygous genetic model (AT vs. TT: P=0.0002, I2=57%), and the random-effects model was performed in these studies.
Publication bias
Begg’s funnel plot and Egger’s test were employed to assess the publication bias. As shown in Figure 2, the funnel plots failed to reveal any obvious asymmetry in all genotypes in overall population. Neither Begg’s test nor Egger’s test showed statistical evidence for publication bias in our meta-analysis (P>0.05).
Figure 2.
Funnel plot assessing evidence of publication bias from 26 studies (A vs. T). Abbreviations: SE, standard error; OR, odds ratio; A vs. G, Allele model.
Discussion
A large amount of evidence suggests that genetics is important in determining the risk of cancer. Related research is to search for the susceptibility genes associated with cancer [46]. It is believed that single nucleotide polymorphism is the most common source of human genetic variation, which may contribute to the susceptibility of individuals to cancer [38-41,47]. In recent years, genetic susceptibility to cancer has caused people’s great interest, and the study on the genetic polymorphism of the tumor is increasing.
Recently, a growing number of epidemiological studies have been performed to assess the association of Interleukin-8-251A/T polymorphisms with GC risk [12-37]. However, the results are conflicting. Thus, we conducted a comprehensive meta-analysis involving published data, to assess the strength of association between the polymorphisms and GC risk.
In this present meta-analysis, 26 studies with 5286 cases and 8000 controls were included. And we explored the association between the potentially functional polymorphisms of Interleukin-8-251A/T and GC risk. In the overall population, the pooled results showed that there was significant association between Interleukin-8-251A/T polymorphism and GC risk in any genetic model: Allele model (A vs. T: OR=1.16, 95% CI=1.05-1.27, P=0.002), dominant model (AA + AT vs. TT: OR=1.22, 95% CI=1.07-1.39, P=0.003) recessive model (AA vs. AT + TT: OR=1.20, 95% CI=1.01-1.41, P=0.03) homozygous genetic model (AA vs. TT: OR=1.31, 95% CI=1.08-1.59, P=0.006) heterozygote comparison (AT vs. TT: OR=1.19, 95% CI=1.04-1.35, P=0.01). In a previous meta-analysis by Wang et al. [39], they failed to find association between Interleukin-8-251A/T polymorphism and gastric cancer susceptibility. This contradiction may result from different sample size and ethnic groups.
In the subgroup analysis by ethnicity, the effects remained in Asians (A vs. T: OR=1.23, 95% CI=1.10-1.37, P=0.0002; AA + AT vs. TT: OR=1.30, 95% CI=1.13-1.49, P=0.0002; AA vs. AT + TT: OR=1.33, 95% CI=1.07-1.64, P=0.009; AA vs. TT: OR=1.49, 95% CI=1.18-1.87, P=0.0009; AT vs. TT: OR=1.25, 95% CI=1.09-1.43, P=0.001). However, no genetic models reached statistical association in Europeans (Table 3). It was partially in line with the results of Cheng (2013)’s [41], Xue (2012)’s [38] and Wang (2012)’s [40] finding. However, there were only 18 studies respectively in their meta-analysis, while 26 studies were involved in our meta-analysis.
The subgroup analysis stratified by Source of controls showed an increased breast cancer risk in hospital-based (HB) studies in any genetic model except recessive model (A vs. T: OR=1.23, 95% CI=1.05-1.43, P=0.01; AA + AT vs. TT: OR=1.40, 95% CI=1.12-1.76, P=0.004; AA vs. TT: OR=1.38, 95% CI=1.02-1.88, P=0.04; AT vs. TT: OR=1.39, 95% CI=1.11-1.74, P=0.004). However, there was no association in any genetic model in population based (PB) studies (Table 3). When stratifying by Genotyping method, we found statistical association in Non-RFLP (restriction fragment length polymorphism) in any genetic model except heterozygote comparison (A vs. T: OR=1.18, 95% CI=1.04-1.35, P=0.01; AA + AT vs. TT: OR=1.23, 95% CI=1.02-1.49, P=0.03; AA vs. AT + TT: OR=1.27, 95% CI=1.01-1.58, P=0.04; AA vs. TT: OR=1.38, 95% CI=1.06-1.80, P=0.02), the effect was remain in PCR-RFLP in dominant model and heterozygote comparison (AA + AT vs. TT: OR=1.20, 95% CI=1.00-1.46, P=0.06; AT vs. TT: OR=1.20, 95% CI=1.00-1.45, P=0.05). Above findings was reported first by the paper.
There are some limitations in this meta-analysis. Firstly, this meta-analysis was based on pooled data. We could not assess the risk of cancer according to stratification of age, Sex and H. pylori infection, smoking, alcohol consumption, environment factors, and other risk factors. Secondly, we just included the published studies in the meta-analysis. It is possible that we missed some related unpublished studies that might meet the inclusion criteria. Moreover, small study effect, in which effects reported in small studies are larger, could not be avoided in that some studies were of a relative small size. Further large scale multicenter studies are warranted to further validate on Interleukin-8-251A/T polymorphisms and GC risk.
Conclusions
In conclusion, this meta-analysis suggests that Interleukin-8-251A/T polymorphism is a risk factor for susceptibility to GC in overall population, especially in Asians, in hospital populations and in Non-RFLP. While, there was no association in Europeans and in general population. Further large scale multicenter epidemiological studies are warranted to confirm this finding.
Disclosure of conflict of interest
None.
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