CD95 rs1800682A/G Variant and Tumor Risk in Asians: Evidence from a Meta-Analysis of 36 Case-Control Studies Containing 22 438 Samples

Background

CD95 (also known as TNFRSF6/Fas/APO-1), is a cell surface receptor and plays a key role in apoptotic signaling pathway in a variety of cell types [1,2]. The CD95 gene is located at chromosome 10q24.1, consisting of 9 exons and 8 introns. One of the single-nucleotide polymorphisms (SNPs) has been widely reported in the promoter region. An A to G transition at nucleotide position -670 (rs1800682), located within the signal transducer and activator of transcription (STAT-1), may influence CD95 expression and deregulate cell death signaling, which could contribute to carcinogenesis [3,4].

Many epidemiologic studies on CD95 rs1800682A/G polymorphism and tumor susceptivity have been reported. However, conclusions across these studies were inconsistent. Considering the vital role of CD95 rs1800682A/G polymorphism in cancer (influencing the CD95 gene expression may lead to tumorigeneses), all eligible case-control studies were identified and selected in our present meta-analysis.

Material and Methods

RETRIEVAL OF STUDIES AND SELECTION CRITERIA:

We systematically searched available studies updated on 1 June 2014 in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) and SinoMed (http://sinomed.imicams.ac.cn) databases. Keywords contained ‘CD95 or Fas or TNFRSF6 or APO-1’, ‘cancer or tumor’, ‘polymorphism or variant’. The inclusion criteria were: (1) case-control study about CD95 rs1800682A/G polymorphism in tumor about Asians; (2) information on each genotype (AA, AG, and GG) in both case and control group. Exclusion criteria were: (1) no control group; (2) insufficient genotype frequency data; (3) reduplicate studies, and (4) study not to accord with Hardy-Weinberg equilibrium (HWE) of controls.

DATA EXTRACTION:

Extracted data included: first author’s last name, publication year, original country, race, cancer category, genotype distribution, and HWE of controls. If 1 tumor was only reported in 1 article, it was placed into the ‘other cancer’ subgroup.

SNP GENOTYPING:

Genotyping for CD95 rs1800682A/G polymorphism was analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), ligase detection reaction-polymerase chain reaction (LDR-PCR), Tetra-amplification refractory mutation system–polymerase chain reaction (T-ARMS-PCR), and TaqMan technology.

QUALITY SCORE ASSESSMENT:

The Newcastle-Ottawa Scale [5] was selected to assess the quality of each study. This measure assesses aspects of methodology in observational studies related to study quality, including selection of cases, comparability of populations, and ascertainment of exposure to risks. The NOS ranges from zero (worst) to 9 stars (best). Studies with a score of 7 stars or greater were considered as high quality.

STATISTICAL ANALYSIS:

All the statistical analysis was performed by Stata software (Version 10.0; StataCorp LP, College Station, TX). Odds ratio (OR) and 95% confidence intervals (CI) were used to assess the strength of the association between the CD95 rs1800682A/G polymorphism and tumor risk. The statistical significance of the summary OR was determined with the Z-test. A heterogeneity assumption was evaluated among studies using the chi-square-based Q-test. When heterogeneity was more than 0.10, Mantel-Haenszel method (fixed-effects model) was used to calculate the pooled OR. Otherwise, DerSimonian and Laird method (random-effects model) was performed [6,7]. The departure of the CD95 rs1800682A/G polymorphism from expected frequencies under HWE was assessed in controls using the Pearson chi-square test. Sensitivity analysis was performed by limiting the meta-analysis to high-quality studies (according to the NOS score). In addition, publication bias was assessed by funnel plots and evaluated by both Egger’s and Begg’s test, respectively. A P<0.05 for Egger’s test or Begg’s test indicates the presence of potential publication bias [8,9].

Results

ELIGIBLE STUDIES AND INCLUDING CHARACTERISTICS:

A total of 217 studies were found in the PubMed (213 articles) and SinoMed (4 articles) databases using keywords. After reviewing the titles and abstracts, 129 articles were excluded; 34 were removed mainly because they were duplications, reviews, clinical trials, letters or comments, meta-analyses, or investigated other site polymorphisms in CD95 or CD95L genes. Subsequently, the remaining 54 publications were further evaluated for eligibility, including 36 case-control studies in Asian populations. The HWE in control group in 3 publications, which were excluded, was not meet with selection criteria. Moreover, the ethnicity of 2 articles was African and mixed, which were also excluded because just 1 paper cannot be combined in meta-analysis. Finally, 34 articles including 36 case-control studies [10–43] were included in the present meta-analysis. The detailed flow chart of study selection is shown in Figure 1. Study characteristics for the association between CD95 rs1800682A/G and tumor risk in Asians are summarized in Table 1. The NOS results show that the average score was 7.08, which indicated that the methodological quality was generally good (Table 2).

POOLED ANALYSIS:

The results of the quantitative synthesis of the data are summarized in Table 3. In the total analysis, there was no association between the CD95 rs1800682A/G polymorphism and whole tumor risk: OR=1.04, 95% CI=0.97–1.12, Pheterogeneity=0.010 (random model) for AA vs. AG+GG, OR=1.01, 95% CI=0.91–1.13, Pheterogeneity=0.015 (random model) for AA vs. GG and OR=0.98, 95% CI=0.89–1.07, Pheterogeneity=0.049 (random model) for AA+AG vs. GG, OR=1.01, 95% CI=0.96–1.07, Pheterogeneity=0.005 (random model) for A-allele vs. G-allele, OR=0.99, 95% CI=0.97–1.01, Pheterogeneity=0.049 (random model) for AG vs. GG. At the same time, no relationship was detected among this SNP and source of control group.

In the subgroup study by the type of cancer, a weak association was found between CD95 rs1800682A/G polymorphism and hepatocellular carcinoma [OR: 0.93, 95% CI: 0.87–0.99, P: 0.521 for heterogeneity (fixed model) and P: 0.035 in dominant model, Figure 2; OR: 0.89, 95% CI: 0.80–0.99, P: 0.506 for heterogeneity (fixed model) and P: 0.036 in heterozygote comparison model (Figure 3). No association was found in other types of cancer, such as breast cancer, lung cancer, breast cancer, gastric cancer, or cervical cancer.

SENSITIVITY ANALYSIS AND PUBLICATION BIAS:

Sensitivity analyses were conducted to determine whether modification of the inclusion criteria of the meta-analysis affected the final results. The included studies were limited to those with high NOS score. For CD95 rs1800682A/G polymorphism, 7 studies with relatively low NOS score (<7) [19,27,28,31,34,40,42] were excluded from the sensitivity analysis. The corresponding pooled ORs were not materially altered. The above results of sensitivity analyses indicated that the overall results were statistically robust. The results of sensitivity analyses are shown in Table 2. The publication bias was assessed by Begg’s funnel plots and Egger’s linear regression test. The shapes of the funnel plots did not reveal asymmetry (such as AA vs. GG: t=0.21, P=0.836; AA+AG vs. GG: t=−0.20, P=0.841, Figures 4 and 5). No statistically significant difference was shown in the Egger’s test, which indicated lack of publication bias in the whole analysis.

Discussion

The global burden of cancer is increasing, with about 12.7 million cancer cases and 7.6 million cancer-related deaths each year [44]. Tumorigenesis is a multi-step and complex process interacting with various environmental and genetic factors. An abundance of evidence has established that gene polymorphisms play a vital role in individual susceptibilities to cancer, such as hepatocellular carcinoma [45–47]. Detection of functional gene polymorphisms, which are associated with cancer risk, may greatly improve cancer prevention and treatment.

The CD95/CD95L system induces the death signal cascade that subsequently results in cell apoptosis [48]. Decreased expression or mutation of CD95 gene has been detected in many types of malignant tumors, which not only impair the sensitivity of tumor cells to apoptotic signal, but also cause tumor cells to evade or weaken the immune elimination through the CD95-CD95L pathway [10]. Considering the important role of the CD95/CD95L system in the apoptotic process of cancer, and down-regulation of CD95 expression by rs1800682 A to G alteration, it is reasonable that CD95 rs1800682A/G polymorphism may affect cancer risk.

It is necessary to analyze associations between CD95 rs1800682A/G polymorphism and cancer risk through using meta-analysis to reach a credible and powerful conclusion. The present analysis is the first to combine all eligible studies, involving 9874 cancer cases and 12 564 controls in Asians. Our study found a weak positive association between CD95 rs1800682A/G and hepatocellular carcinoma, but no association was found with other cancers. There are 2 possible explanations for this phenomenon. On the one hand, cancer is a multifactorial disease because complicated interactions between several genetic and environmental factors may influence the development of cancer. On the other hand, no single gene or single environmental factor determines cancer risk [49].

For better interpreting the results, 2 potential limitations of our meta-analysis should be considered. First the sample size in most of the included studies was small, which may increase the probability of false-positives or false-negatives. Secondly, gene-gene and gene-environment interactions and other covariates, such as age, sex, family history, and lifestyle, should be reported and re-analyzed, because the expression of 1 gene may be influenced by other genes or environment factors.

Conclusions

Our analysis found a weak association between CD95 rs1800682A/G polymorphism and hepatocellular carcinoma risk in Asians. Well-designed studies with larger sample sizes and including gene-gene and gene-environment factors are needed to explain and confirm our findings.