Fas −670A/G (rs1800682) Polymorphism and Digestive Cancer Risk in Asians: A Meta-Analysis

Abstract

Objectives: Tumorigenesis is a multistep process that begins with the abrogation of normal controls of apoptosis and cell proliferation, and the Fas receptor-ligand system is a key regulator of apoptosis. The Fas −670 A/G single-nucleotide polymorphism (SNP) has been demonstrated to affect the expression of the Fas gene by altering the transcriptional activity in this gene's promoter. However, the association between the Fas −670 A/G polymorphism and digestive cancer risk is still controversial and ambiguous in the Asian population, so we conducted a meta-analysis to confirm and clarify the association between the Fas −670 A/G polymorphism and digestive cancer. Materials and Methods: A search of PubMed, China National Knowledge Infrastructure (CNKI), and WanFang databases was conducted and encompassed all available articles that had been published up to July 20, 2013. Overall, 15 case-control studies containing 3692 cases and 4895 controls were retrieved based on search criteria for digestive cancer susceptibility related to −670A/G SNP. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the strength of this association. Results: In the overall analysis, the country type and source of control subgroups, no association between the Fas −670 A/G polymorphism and digestive cancer risk was found. However, in the digestive cancer-type subgroups, a significant protective effect was detected between Fas −670 A/G polymorphism and hepatocellular carcinoma in Asians (AG vs. GG: OR=0.89, 95% CI=0.80-0.99; AA+AG vs. GG: OR=0.93, 95% CI=0.87-1.00). Conclusions: Our investigations demonstrated that the Fas −670 A/G polymorphism might decrease the hepatocellular carcinoma risk in Asian populations. Further studies based on larger sample sizes, other ethnicities, and gene-environment interactions should be conducted to further understand the role of Fas −670 A/G polymorphism in digestive cancer risk.

Introduction

Apoptosis is the physiological mechanism of programmed cell death that is crucial for normal tissue development and homeostasis (Danial and Korsmeyer, 2004). The aberrant regulation of apoptosis correlates with a variety of human diseases, including cancer (Lowe and Lin, 2000; Evan and Vousden, 2001). Fas (TNFRSF6/APO-1), which is known as a member of the tumor necrosis factor receptor superfamily, is a transmembrane receptor involved in apoptotic signal transmissions in many types of cells. The death signal cascade is initiated upon crosslinking of Fas with its natural ligand (FasL) (Nagata and Golstein, 1995). Decreased expression or mutation of the Fas gene has been found in many malignant tumors. This decreased expression or mutation impairs the sensitivity of tumor cells to apoptotic signals and allows tumor cells to evade or weaken the ability of the immune system to eliminate them from the body through the Fas-FasL pathway (Gastman et al., 1999; Lee et al., 1999; Viard-Leveugle et al., 2003). It is well known that the development of cancer is not only associated with the unlimited proliferation of cells but also with the suppression of apoptosis.

A single-nucleotide polymorphism (SNP) at −670 of the Fas gene promoter (A to G substitution) (rs1800682) has been found with potentially altered transcriptional efficiency, which implies that this SNP may affect the occurrence and progression of apoptosis-related disorders (Kanemitsu et al., 2002). The Fas −670G allele disrupts STAT1 transcription factor binding sites and, thus, diminishes the promoter activity and decreases Fas gene expression (Huang et al., 1997; Kanemitsu et al., 2002). This indicates that the A allele may protect transformed cells against apoptosis, whereas the G allele may be a risk factor for cancer.

So far, there have been many studies that investigated the role of Fas −670A/G polymorphism and digestive cancer risk in the Asian region; however, results have been inconsistent due to different countries, case ascertainment, and small sample sizes. Thus, previous studies had the potential for false-positive findings as well as limited power to detect modest associations. To our knowledge, this is the most comprehensive meta-analysis, which has been conducted to date that examines the association between the Fas −670A/G polymorphism and digestive cancer risk in Asians.

Materials and Methods

Eligibility of relevant studies

Searches were conducted in the PubMed and Chinese language (China National Knowledge Infrastructure [CNKI] and WanFang) databases using key words containing “Fas”, “cancer” or “carcinoma” or “tumor”, and “polymorphism” or “variant”. No restrictions were placed on language or publication year and the last search was updated on July 20, 2013. A total of 174 articles were retrieved using the above terms of which, 15 articles contained the inclusion criteria.

Criteria and data extraction

Included studies had to meet the following criteria: the study assessed the correlation between digestive cancer risk and the Fas-670A/G polymorphism in an Asian population, the study was case controlled, and the study contained sufficient genotype numbers for cases and controls. On the other hand, the following exclusion criteria were used: there was no control population, there were no available genotype frequency data, and the study was a duplicate. The following items were collected: the last name of first author, year of publication, country of origin, ethnicity, digestive cancer type, the total and number of each genotype frequency in case-control groups, source of control, Hardy-Weinberg equilibrium (HWE) of controls, and genotyping methods. A subgroup analysis, stratified by cancer type, was performed. If a cancer type appeared in only one study, it was placed into the other cancer subgroup. Source of control subgroup analysis was performed on two groups and was classified as population based (PB) or hospital based (HB).

Statistical analysis

Odds ratios (ORs) with 95% confidence intervals (CIs) were used to measure the strength of the association between the Fas −670A/G polymorphism and digestive cancer risk based on genotype frequencies in cases and controls. The fixed-effects model and the random-effects model were used to calculate the pooled OR value. The statistical significance of the summary OR was determined with the Z-test. Heterogeneity assumption was evaluated among the studies with a chi-square-based Q-test. A p-value of more than 0.10 for the Q-test indicated a lack of heterogeneity among the studies. If significant heterogeneity was detected, the random-effects model was used. Otherwise, the fixed-effects model was chosen (Mantel and Haenszel, 1959; DerSimonian and Laird, 1986). We investigated the relationship between genetic variants of the Fas −670 site and digestive cancer risk by allelic contrast (A allele vs. G allele), comparison of homozygotes (AA vs. GG), comparison of heterozygotes (AG vs. GG), the dominant model (AA+AG vs. GG), and the recessive model (AA vs. AG+GG). The departure of the Fas −670A/G polymorphism from expected frequencies under HWE was assessed in controls by the χ² test using the Pearson chi-square test; p<0.05 was considered significant. Publication bias was diagnosed using Egger's linear regression method and funnel plot. A p-value <0.05 in Egger's linear regression indicated the presence of potential publication bias (Hayashino et al., 2005). All statistical tests for this meta-analysis were performed with Stata software (version 10.0; StataCorp LP, College Station, TX).

Results

Studies characteristics

A total of 174 articles were collected from the PubMed and Chinese language (CNKI and WanFang) databases through literature search, using different combinations of key terms. Finally, 15 articles, including 3692 cases and 4895 controls, were identified (Kim et al., 2003; Sun et al., 2004; Ikehara et al., 2006; Jain et al., 2007; Jung et al., 2007; Hsu et al., 2008; Yang et al., 2008; Chen et al., 2009; Wang et al., 2009, 2010, 2013; Zhang et al., 2009; Zhou et al., 2010; Zhu et al., 2010; Hu et al., 2011) (Fig. 1). Study characteristics from published studies on the relationship between Fas −670 A/G polymorphism and digestive cancer risk are summarized in Table 1. The distribution of genotypes among controls was consistent with HWE in all studies, except one (Wang et al., 2010). In most of the studies, the cases were histologically diagnosed and the controls were free of cancer.

FIG. 1.

Flowchart illustrating the search strategy used to identify association studies of Fas −670 A/G polymorphisms and digestive cancer risk for the meta-analysis.

Table 1.

Characteristics of Studies of Fas −670A/G Polymorphism and Digestive Cancer Risk Included in Our Meta-Analysis

							Case			Control
First author	Year	Country	Digestive cancer type	Case	Control	Source of control	AA	AG	GG	AA	AG	GG	HWE	Genotype method
Kim	2003	Korea	Hepatocellular carcinoma	99	240	PB	30	41	28	78	118	44	0.957	PCR-RFLP
Sun	2005	China	Esophageal cancer	588	648	PB	224	247	117	246	321	81	0.130	PCR-RFLP
Ikehara	2006	Japan	Gastric cancer	271	271	HB	62	141	68	71	130	70	0.504	PCR-RFLP
Jain	2007	India	Esophageal cancer	151	201	PB	57	78	16	66	107	28	0.140	PCR
Jung	2007	Korea	Hepatocellular carcinoma	312	328	PB	98	140	74	93	168	67	0.576	TaqMan
Hsu	2008	China-Taiwan	Gastric cancer	86	101	PB	25	47	14	33	48	20	0.736	PCR-RFLP
Yang	2008	China	Pancreatic cancer	397	907	PB	158	182	57	357	419	131	0.653	PCR-RFLP
Zhang	2009	China	Hepatocellular carcinoma	45	36	HB	9	27	9	21	11	4	0.200	PCR-RFLP
Chen	2009	China	Esophageal cancer	188	324	PB	82	84	22	130	158	36	0.242	PCR-RFLP
Wang	2009	China	Gastric cancer	332	324	PB	116	172	44	132	148	44	0.806	PCR-RFLP
Zhu	2010	China	Nasopharyngeal carcinoma	237	264	HB	79	124	34	93	132	39	0.478	PCR-RFLP
Zhou	2010	China	Gastric cardiac carcinoma	262	524	PB	105	121	36	186	266	72	0.133	PCR-RFLP
Wang	2010	China-Taiwan	Oral squamous cell carcinoma	294	333	PB	90	144	60	106	180	47	0.034	PCR-RFLP
Hu	2011	China	Gastric cancer	129	95	HB	54	61	14	28	47	20	0.973	PCR-RFLP
Wang	2013	China	Larynx and hypopharynx carcinoma	301	299	PB	124	140	37	122	136	41	0.752	PCR-RFLP

HB, hospital based; HWE, Hardy-Weinberg equilibrium; PB, population-based; PCR-RFLP, polymerase chain reaction and restriction fragment length polymorphism.

Quantitative synthesis

The results of the overall meta-analysis suggested no association between the Fas −670A/G polymorphism and digestive cancer susceptibility (allelic contrast: OR=0.97, 95% CI=0.89-1.06, p_{heterogeneity}=0.036; heterozygote comparison: OR=0.91, 95% CI=0.76-1.09, p_{heterogeneity}=0.034; homozygote comparison: OR=0.93, 95% CI=0.71-1.11, p_{heterogeneity}=0.048; dominant model: OR=0.92, 95% CI=0.78-1.08, p_{heterogeneity}=0.035; and recessive model: OR=1.00, 95% CI=0.88-1.13, p_{heterogeneity}=0.060). Similarly, no association was found in the Chinese people and in the source of control subgroup (Table 2).

Table 2.

Stratified Analyses of Fas −670A/G Gene Polymorphism on Digestive Cancer Risk

			Allelic contrast			Homozygote comparison			Heterozygote comparison
Variables	n	Cases/controls	OR (95% CI)	p^a	p	OR (95% CI)	p^a	p	OR (95% CI)	p^a	p
Total	15	3692/4895	0.97 (0.89-1.06)	0.036	0.540	0.93 (0.77-1.11)	0.048	0.409	0.91 (0.76-1.09)	0.034	0.299
Country
China	11	2859/3855	0.97 (0.87-1.09)	0.018	0.627	0.93 (0.74-1.17)	0.027	0.545	0.93 (0.75-1.16)	0.033	0.532
Others	4	833/1040	0.99 (0.93-1.05)	0.336	0.725	0.97 (0.87-1.08)	0.272	0.562	0.96 (0.89-1.03)	0.125	0.291
Source of control
HB	4	682/666	0.93 (0.63-1.36)	0.002	0.698	0.96 (0.48-1.93)	0.010	0.917	1.05 (0.97-1.13)	0.709	0.255
PB	11	3010/4229	0.96 (0.90-1.03)	0.473	0.303	0.97 (0.93-1.01)	0.227	0.099	0.84 (0.69-1.03)	0.046	0.094
Cancer type
Gastric cancer	5	1080/1315	1.01 (0.96-1.06)	0.121	0.637	1.02 (0.95-1.11)	0.237	0.561	1.03 (0.97-1.10)	0.599	0.268
Hepatocellular carcinoma	3	456/604	0.73 (0.47-1.13)	0.014	0.153	0.62 (0.32-1.21)	0.073	0.161	0.89 (0.80-0.99)	0.506	0.036
Esophageal cancer	3	927/1173	0.98 (0.94-1.03)	0.111	0.446	0.93 (0.55-1.56)	0.057	0.772	0.79 (0.46-1.33)	0.048	0.370
Other cancer	4	1229/1803	0.99 (0.95-1.03)	0.617	0.608	0.98 (0.92-1.05)	0.399	0.109	0.98 (0.93-1.03)	0.237	0.478

			Dominant genetic model			Recessive genetic model
			OR (95% CI)	p^a	p	OR (95% CI)	p^a	p
Total	15	3692/4895	0.92 (0.78-1.08)	0.035	0.304	1.00 (0.88-1.13)	0.060	0.969
Country
China	11	2859/3855	0.93 (0.76-1.15)	0.030	0.513	0.98 (0.84-1.15)	0.025	0.840
Others	4	833/1040	0.98 (0.93-1.03)	0.150	0.339	1.02 (0.89-1.18)	0.486	0.750
Source of control
HB	4	682/666	1.02 (0.97-1.07)	0.196	0.458	0.79 (0.44-1.42)	0.001	0.438
PB	11	3010/4229	0.86 (0.72-1.03)	0.078	0.108	1.01 (0.95-1.08)	0.769	0.655
Cancer type
Gastric cancer	5	1080/1315	1.02 (0.98-1.06)	0.465	0.328	1.01 (0.77-1.32)	0.072	0.960
Hepatocellular carcinoma	3	456/604	0.93 (0.87-1.00)	0.521	0.035	0.66 (0.30-1.46)	0.002	0.303
Esophageal cancer	3	927/1173	0.85 (0.50-1.44)	0.037	0.545	1.05 (0.94-1.17)	0.645	0.423
Other cancer	4	1229/1803	0.99 (0.96-1.02)	0.232	0.463	0.99 (0.90-1.09)	0.958	0.847

The bold in this table means significant association between FAS −670A/G polymorphism and digestive cancer risk.

p: Value of Q-test for heterogeneity test.

p^a: Random-effects model was used when p-value for heterogeneity test<0.10; otherwise, fixed-effects model was used.

CIs, confidence intervals; ORs, odds ratios.

In the stratified analysis by digestive cancer type, a significant association was identified between the Fas −670A/G polymorphism and hepatocellular carcinoma (heterozygote comparison: OR=0.89, 95% CI=0.80-0.99, p_{heterogeneity}=0.506, p=0.036, Fig. 2 and dominant model: OR=0.93, 95% CI=0.87-1.00, p_{heterogeneity}=0.521, p=0.035, Fig. 3), but not for gastric cancer, esophageal cancer, and other cancers (Table 2).

FIG. 2.

Forest plot of digestive cancer risk associated with the Fas −670 A/G polymorphism (AG vs. GG) by cancer-type subgroup. The squares and horizontal lines correspond to the study-specific ORs and 95% CIs. The area of the squares reflects the weight (inverse of the variance). The diamond represents the summary OR and 95% CI. CIs, confidence intervals; ORs, odds ratios.

FIG. 3.

Forest plot of digestive cancer risk associated with the Fas −670 A/G polymorphism (AA+AG vs. GG) by cancer-type subgroup. The squares and horizontal lines correspond to the study-specific ORs and 95% CIs. The area of the squares reflects the weight (inverse of the variance). The diamond represents the summary OR and 95% CI.

Bias diagnosis

The Egger's test was performed to assess the publication bias of literature, and was used to provide statistical evidence of funnel plot symmetry. Ultimately, the results did not provide any evidence of publication bias.

Discussion

Antitumor T lymphocytes could be induced to undergo apoptosis after activation by tumor-associated or tumor-specific antigens, which may lead to escaping of cancer cells from antitumor immunosurveillance (Green et al., 2003). Activation-induced cell death of T lymphocytes is mainly initiated by Fas and FasL interaction (Suda et al., 1993; O'Connell et al., 1996). It has been found that there is reduced expression of FAS, but enhanced expression of FasL in many cancers (Rabinowich et al., 1998). The aberration of expression of Fas and/or FasL genes leads to cancer cells resisting the killing of anticancer T lymphocytes and malignant transformation.

Genetic susceptibility to cancers has led to growing attention to the studies of polymorphism of genes involved in carcinogenesis, which, if large and unbiased, can provide insight into the relationships between candidate genes and digestive cancer risk. However, there has been a continuing debate over the association between Fas −670A/G polymorphism and digestive cancer risk; previous studies have generally been underpowered to draw a convincing conclusion. The meta-analysis is a method that can solve the problem created by low statistical power in a single study to draw a more robust conclusion from the body of evidence.

The current report is a timely analysis that combines the findings of all previous publications that evaluated the Fas −670A/G polymorphism and digestive cancer risk in Asians. We performed a meta-analysis involving 3692 digestive cancer cases and 4895 controls. In the overall analysis, no association was found between the Fas −670A/G polymorphism and digestive cancer susceptibility in all genetic models. Similar findings were also indicated in the source of control subgroup. The main message of our meta-analysis is that there was a significant relationship between Fas −670A/G polymorphism and hepatocellular carcinoma risk, which suggests that the −670A allele in the Fas gene protects against the development of hepatocellular carcinoma and that the −670G allele confers an increased risk for the development of hepatocellular carcinoma. There must be some factors that would contribute to this discrepancy. First, Fas −670A/G polymorphism might play a different role in different digestive cancers. Second, multiple genes and environmental factors may lead to digestive cancer formation. Third, time lag bias and publication bias may also play a role in our meta-analysis.

Meta-analysis is recognized as an effective method for solving a wide variety of clinical questions by summarizing and reviewing published quantitative studies. Although meta-analysis could increase statistical power, it could not replace independent research due to differences in molecular mechanism in different types of digestive cancers. What is more, larger sample, multicenter, PB studies, which comprise gene-gene interactions and gene-environment interactions, should be carried out for the same digestive cancer; based on these, our meta-analysis would acquire much more effective statistical power. In spite of these limitations, there were two advantages in our meta-analysis. First, a substantial number of cases and controls were pooled from different studies, which significantly increased statistical power of the analysis. Second, the quality of case-control studies included in the current meta-analysis was satisfactory based on our selection criteria.

In summary, in the present meta-analysis, a significantly decreased association was found between Fas −670 A/G polymorphism and hepatocellular carcinoma risk in Asians. Therefore, further large studies, particularly, examining gene-gene and gene-environment interactions, are warranted. These future studies could lead to a better and more comprehensive understanding of the association between the Fas −670A/G polymorphism and development of digestive cancer risk.

Footnotes

Acknowledgments

The authors declare that they have no competing interests.

Author Disclosure Statement

No competing financial interests exist.

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