552310
research-article2014
JRA0010.1177/1470320314552310Journal of the Renin-Angiotensin-Aldosterone SystemWang et al.
Original Article
Angiotensin-converting enzyme insertion/ deletion gene polymorphism and lung cancer risk: A meta-analysis
Journal of the Renin-AngiotensinAldosterone System 2015, Vol. 16(1) 189–194 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1470320314552310 jra.sagepub.com
Nan Wang1, DaFu Yang1, Bin Ji1 and JianYou Li2
Abstract Objective: Angiotensin-converting enzyme (ACE) I/D polymorphism has been reported to be associated with lung cancer, but the results of previous studies are conflicting. The present study was designed to investigate the association between this polymorphism and the risk of lung cancer using a meta-analysis of the published studies. Methods: Two investigators independently searched the PubMed, Embase and CNKI databases. This meta-analysis covered six case-control studies, including 807 lung cancer patients and 816 healthy controls. Results: The results of this meta-analysis based on all the studies showed no significant association between ACE I/D gene polymorphism and lung cancer risk (DD vs II: OR = 1.18, 95% CI = 0.68–2.04; DI vs II: OR = 0.93, 95% CI = 0.56–1.53; DD+DI vs II: OR = 1.01, 95% CI = 0.68–1.50; DD vs II+DD: OR =1.11, 95% CI = 0.73–1.71). In the subgroup analysis by race and the larger studies (n > 200 participants), no significant associations between the ACE I/D polymorphism and risk of lung cancer were indicated. However, when the analyses were restricted to small studies (n ≤ 200 participants), a significantly higher risk was observed (DD vs II: OR = 2.57, 95% CI = 1.24–5.30). Conclusions: This meta-analysis suggests that the ACE gene I/D polymorphism may not be associated with the risk of lung cancer, and the observed increase in the risk of lung cancer may be due to small-study bias. Keywords ACE, gene polymorphism, lung cancer, meta-analysis Date received 21 December 2013; accepted 25 July 2014
Introduction According to the International Agency for Research on Cancer of the World Health Organization, lung cancer is the most common cancer in the world, with an estimated 1.6 million new cases in 2008, representing one in eight of all new cancer cases. It is also the most common form of cancer death in the world, comprising nearly one in five of all deaths from cancer.1 There are many factors contributing to lung cancer, of which environmental exposure, primarily to smoking, is the major risk factor. However, not all lung cancers are due to smoking, and increasing evidence for the association between genetic factors and identified lung cancer risk has been accumulated in hundreds of studies.2 Existing evidence has suggested that genetic factors also play an important role in the pathogenesis of lung cancer.3 Angiotensin-converting enzyme (ACE) is a zinc metallopeptidase that converts angiotensin I to angiotensin II (vasoconstrictor) and degrades bradykinin (vasodilator), regulating blood pressure and cardiovascular homeostasis.4 Approximately 90% of the physiologic conversion
of angiotensin I to angiotensin II takes place in the lungs. ACE in peripheral blood is thought to be identical to the lung enzyme and is proportional to blood oxygen concentration, suggesting that serum ACE activity is closely correlated with the enzyme concentration in the pulmonary tissue.5 ACE plasma levels depend on a 287 bp insertion/ deletion (I/D) polymorphism of the ACE gene located on chromosome 17q23.6 Homozygotes for the D allele have the highest ACE plasma levels, homozygotes for the I
1Medical
Department, Huzhou Traditional Chinese Medicine Hospital, People’s Republic of China 2Medical Department, Huzhou Central Hospital, People’s Republic of China Corresponding author: JianYou Li, Medical Department, Huzhou Central Hospital, 198 Hongqi Road, Huzhou 313000, People’s Republic of China. Email: [email protected]
Creative Commons CC-BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 License (http://www.creativecommons.org/licenses/by-nc/3.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (http://www.uk.sagepub.com/aboutus/openaccess.htm). Downloaded from jra.sagepub.com at MICHIGAN STATE UNIV on April 6, 2015
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allele have the lowest, and ID heterozygotes have intermediate levels. Over the past few years, many studies have shown that the ACE I/D polymorphism may be closely associated with the risk of cancer, including breast, gastric, and prostate cancer. In addition, though, several studies found an association between ACE I/D polymorphism and lung cancer while others did not, suggesting that it may serve as a possible risk factor for lung cancer. Meta-analysis can be a useful tool in the detection of associations that could otherwise remain unseen in studies with small sample sizes, especially studies evaluating rare allele frequency polymorphisms.7 This has recently become an important part of genetic research, mainly because it can reconcile previously conducted studies that gave inconsistent results. The present study investigated, by performing a meta-analysis, whether the ACE I/D polymorphism is associated with lung cancer risk.
Data extraction Data were independently extracted by two investigators (Nan Wang and JianYou Li), and a consensus was reached on all of the items. To ensure quality, the most recent and complete articles were chosen if a study was published more than once. First author, year of publication, country, nationality, number of patients and controls, gene polymorphisms and evidence of Hardy-Weinberg equilibrium (HWE) were documented. Any encountered discrepancies were adjudicated by a discussion and a 100% consensus was reached.
Statistical analysis
Literature databases including PubMed, Embase and China National Knowledge Infrastructure (CNKI) databases were searched for all articles on any association between ACE I/D polymorphism and the risk of lung cancer (last search update November 30, 2013). The search strategy was designed to identify all possible studies using the following keywords: “ACE I/D,” ”lung cancer,” “polymorphism,” “single nucleotide polymorphism” and “genetic polymorphism.” The search was not restricted by language, but all included studies had to be conducted on humans. Reference lists of previous reviews and meta-analyses were searched manually. Unpublished reports were not considered. If more than one article was published by the same author using the same case series, the study covering the greater number of individuals was included.
We assessed HWE in the controls for each study using the goodness-of-fit test (chi-square or Fisher exact test) and p < 0.05 was considered as significant disequilibrium. ORs were used as a measure of the association between the ACE I/D polymorphism and risk of lung cancer under a homozygote comparison (DD vs II), a heterozygote comparison (DI vs II), a dominant model (DD+DI vs II) and a recessive mode (DD vs II+DI) between groups.8 Both the Cochran’s Q statistic to test for heterogeneity and the I2 statistic to quantify the proportion of the total variation due to heterogeneity were calculated. A p value of more than the nominal level of 0.10 for the Q statistic indicated a lack of heterogeneity across studies, allowing for the use of a fixed-effects model; otherwise, the random-effects model was used. We examined the following study characteristics: ethnicity and study sample size (≤200 and >200 individuals). Sensitivity analysis was performed to assess the stability of the results. Publication bias was investigated with a funnel plot, which is the main graphical method of assessing bias. To supplement the funnel plot approach, the Begg’s test was adopted (p < 0.05 was considered statistically significant). Data analysis was performed using STATA version 12.0 (StataCorp LP, College Station, TX, USA).
Inclusion and exclusion criteria
Results
The studies included in the meta-analysis met all of the following inclusion criteria: (1) case-control studies conducted to evaluate the association between the ACE I/D polymorphism and the risk of lung cancer; (2) sufficient genotype data to calculate the odds ratios (ORs) and 95% confidence intervals (CIs); and (3) the paper clearly described the sources of cases and controls. Major exclusion criteria were as follows: (1) studies lacking case-control evaluation of the association between ACE I/D polymorphism and risk of lung cancer; (2) case reports, letters, reviews, meta-analyses and editorial articles; (3) studies based on incomplete raw data or for which no usable data were reported; and (4) duplicate studies.
Study characteristics
Materials and methods Literature search strategy
A total of 151 articles were gleaned by a literature search of PubMed, Embase and CNKI databases, using different combinations of key terms. As shown in Figure 1, a final total of six case-control studies met our inclusion criteria,9–14 including 807 cases and 816 controls. The genotype distributions in the controls of all studies were in agreement with HWE. There were three studies of Europeans12–14 and three of Asians.9–11 The information from these six studies and the numbers of cases and controls with II, DI and DD genotypes reported in each study are all presented in Table 1.
Downloaded from jra.sagepub.com at MICHIGAN STATE UNIV on April 6, 2015
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Figure 1. Flow diagram of the study search and selection process.
CNKI: China National Knowledge Infrastructure; ACE: angiotensin-converting enzyme; I: insertion; D: deletion.
Table 1. Characteristics of the included studies for meta-analysis. Study included
Year
Area
Ethnicity
Cases/ Controls
Cheon et al.9 Wang et al.10 Zhang et al.11 Yaren et al.12 Nacak et al.13 Dević Pavlić et al.14
2000 2000 2005 2008 2010 2012
Korea China China Turkey Turkey Croatia
Asian Asian Asian Caucasian Caucasian Caucasian
218/121 34/38 47/54 75/85 125/165 308/353
Genotypes for cases
Genotypes for controls
HWE test
II DI DD
II DI DD
72 116 30 10 6 18 21 21 5 4 39 32 37 50 38 64 148 96
48 50 23 13 18 7 20 30 4 14 37 34 29 72 64 78 177 98
0.13 0.86 0.11 0.47 0.27 0.91
HWE: Hardy-Weinberg equilibrium.
Quantitative synthesis The evaluation of an association between the ACE I/D polymorphism and the risk of lung cancer is displayed in Table 2. The results of this meta-analysis showed no significant association between the ACE I/D polymorphism and lung cancer risk in any of the genetic models (Figure 2, DD vs II: OR = 1.18, 95% CI = 0.68–2.04; DI vs II: OR = 0.93, 95% CI = 0.56–1.53; DD+DI vs II: OR = 1.01, 95% CI = 0.68–1.50; DD vs II+DI: OR = 1.11, 95% CI = 0.73– 1.71). In a subgroup analysis by ethnicity, the studies included were divided into Asian and Caucasian populations, and no significant association was found between the ACE I/D polymorphism and lung cancer risk in Asians (DD vs II: OR = 1.20, 95% CI = 0.71–2.03; DI vs II: OR = 0.76, 95% CI = 0.30–1.92; DD+DI vs II: OR = 1.07, 95% CI = 0.74–1.54; DD vs II+DI: OR = 1.64, 95% CI = 0.45– 6.01) and in Caucasians (DD vs II: OR = 1.09, 95% CI = 0.45–2.66; DI vs II: OR = 1.08, 95% CI = 0.50–2.35; DD+DI vs II: OR = 1.08, 95% CI = 0.50–2.42; DD vs
II+DI: OR = 1.01, 95% CI = 0.79–1.30). However, when the analyses were restricted to three small studies (n ≤ 200 participants), meta-analysis results showed a significant association with the risk of lung cancer (DD vs II: OR = 2.57, 95% CI = 1.24–5.30). Sensitivity analyses were conducted by altering the statistic models. No material alteration was detected, indicating that our results were statistically robust (DD vs II: OR = 1.05, 95% CI = 0.79– 1.39; DI vs II: OR = 0.97, 95% CI = 0.77–1.26; DD+DI vs II: OR = 1.00, 95% CI = 0.79–1.26; DD vs II+DI: OR = 1.05, 95% CI = 0.84–1.31).
Publication bias The publication bias of the meta-analysis of the association between the ACE I/D polymorphism and lung cancer risk was detected by Begg’s funnel plot; all graphical funnel plots of the included studies appeared to be symmetrical. Results showed that there was no publication bias (DD vs II: Begg’s test, p = 1.00, Egger test; DI vs II: Begg’s
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Table 2. Stratified analyses of the ACE I/D polymorphism and risk of lung cancer. Variables
Cases/ controls
DD vs II
DI vs II
DD+DI vs II
DD vs II+DI
OR (95% CI) p
OR (95% CI) p
OR (95% CI) p
OR (95% CI) p
6
807/816
1.18 (0.68–2.04) 0.02
0.93 (0.56–1.53) 0.01
1.01 (0.68–1.50) 0.04
3 3
299/213 508/603
1.20 (0.71–2.03) 0.16 1.09 (0.45–2.66) 0.01
0.76 (0.30–1.92) 0.02 1.08 (0.50–2.35) 0.02
1.07 (0.74–1.54) 0.57 1.08 (0.50–2.42) 0.01
3 3
651/639 156/177
0.81 (0.46–1.42) 0.05 2.57 (1.24–5.30) 0.49
0.98 (0.58–1.65) 0.03 0.89 (0.24–3.31) 0.01
0.89 (0.56–1.42) 0.05 1.36 (0.57–3.26) 0.09
1.11 (0.73–1.71) 0.02 1.64 (0.45–6.01) 0.01 1.01 (0.79–1.30) 0.20 0.86 (0.58–1.29) 0.11 1.94 (0.74–5.09) 0.06
N
Total Ethnicity Asian Caucasian Sample size >200 ≤200
N = number of comparisons; p value of the Q-test for heterogeneity test. Random-effects model was used when p value for heterogeneity test 0.05, Figure 3).
Discussion Genetic polymorphisms that alter the amount of protein expressed may have a substantial influence on disease activity.15 Lung cancer is a complex disease, and many factors, including environmental and occupational exposure, cigarette smoking, and genetics, contribute to its progression. The I/D polymorphism accounts for 20% to 50% of the variance in ACE expression or activity in blood and tissues among individuals.16 The relationship between ACE I/D polymorphism and risk of lung cancer has been addressed in several studies, and the results are controversial. An apparent discrepancy in the results may be due to ethnic differences, or to insufficient sample size. The aim of meta-analysis is to combine the same kinds of studies to increase the sample size and statistical power, thereby producing more authentic results. This is the first meta-analysis to consider ACE I/D polymorphism and the risk of lung cancer. In the current metaanalysis, the association between ACE I/D polymorphism and the risk of lung cancer was examined by critically including all published studies. Ultimately, only six case-control studies were included, comprising a total of 807 patients and 816 healthy controls. The final results of this meta-analysis did not show any significant association between ACE I/D polymorphism and the risk of lung cancer. Because results may be affected by ethnicity, a race-related subgroup analysis was performed, and no significant association was found
between ACE I/D polymorphism and susceptibility to lung cancer in either Caucasian or Asian populations. When stratifying by sample size (≤200), this meta-analysis detected a significant association between ACE I/D polymorphism and lung cancer. However, this conclusion was drawn using a small number of samples, which suggests that the observed associations between ACE I/D polymorphism and an increased lung cancer risk reflect chance observations rather than true associations, which is a small-study bias. Further sensitivity analysis confirmed the significance of the association between ACE I/D polymorphism and risk of lung cancer. No evidence collected in this meta-analysis indicated publication bias (p > 0.05). The potential influence of ACE I/D polymorphism may be affected by gene-gene and gene-environment interactions. The effects of ACE I/D polymorphism on lung cancer may be attributable to linkage disequilibrium with the ACE gene A-240T and A2350G polymorphisms.17 In addition, nicotine and its metabolites increase the expression and activity of ACE in human endothelial cells,18 and higher levels of circulating ACE, which are associated with the ACE I/D polymorphism, are found in male smokers.19 This suggests that the ACE I/D polymorphism may be correlated with tobacco smoking and with an increased risk of lung cancer development. However, one study could not be included in this meta-analysis, and further studies of genegene and gene-environment interactions must be taken into consideration for assessment of the risk of lung cancer. The current meta-analysis has some limitations in this meta-analysis: 1) Only published studies were included, so publication bias may be an issue, even though the use of a
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statistical test did not indicate any; 2) because of incomplete raw data or publication limitations, some relevant studies could not be included in our analysis; and 3) genegene and gene-environment interactions were not tested in the present study because of the lack of information from the original studies. In conclusion, this meta-analysis indicates that the ACE I/D polymorphism may be not associated with lung cancer risk, and the observed increase in the risk of lung cancer may be due to small-study bias. Because few studies are available in this field and because current evidence remains limited, large studies of adequate methodological quality, properly controlling for possible confounding factors, are greatly needed. Acknowledgement We thank LetPub (www.letpub.com) for its linguistic assistance.
Conflict of interest None declared.
Funding This work was supported by a grant from Zhejiang Science and Technology R&D Fund (2014C33245), the Medical Scientific Research Foundation of Zhejiang Province (2012RCB039), and the Huzhou Science and Technology R&D Fund (2012YS02).
References 1. Mitsudomi T. Advances in target therapy for lung cancer. Jpn J Clin Oncol 2010; 40: 101–106. 2. Brennan P, Hainaut P and Boffetta P. Genetics of lung-cancer susceptibility. Lancet Oncol 2011; 12: 399–408. 3. Herbst RS, Heymach JV and Lippman SM. Lung cancer. N Engl J Med 2008; 359: 1367–1380. 4. van der Knaap R, Siemens C, Coebergh JW, et al. Renin angiotensin system inhibitors, angiotensin I-converting enzyme gene insertion/deletion polymorphism and cancer: The Rotterdam Study. Cancer 2008; 112: 748–757. 5. Barát E, Böszörményi-Nagy G and Debreczeni LA. Serum angiotensin converting enzyme values in chronic obstructive pulmonary disease. Acta Physiol Hung 1987; 70: 337–342. 6. Castellon R and Hamdi HK. Demystifying the ACE polymorphism: From genetics to biology. Curr Pharm Des 2007; 13: 1191–1198. 7. Attia J, Thakkinstian A and D’Este C. Meta-analyses of molecular association studies: Methodologic lessons for genetic epidemiology. J Clin Epidemiol 2003; 56: 297–303.
8. Niu W, Qi Y, Gao PJ, et al. Review: Association between angiotensin converting enzyme G2350A polymorphism and hypertension risk: A meta-analysis. J Renin Angiotensin Aldosterone Syst 2011; 12: 8–14. 9. Cheon KT, Choi KH, Lee HB, et al. Gene polymorphisms of endothelial nitric oxide synthase and angiotensin-converting enzyme in patients with lung cancer. Lung 2000; 178: 351–360. 10. Wang HW, Nie ZS, Duan YZ, et al. Association between polymorphism in ACE gene with lung cancer and COPD patients [article in Chinese]. Bei Jing Yi Xue 2000; 22: 364– 365. 11. Zhang QZ, Liu XM, Zhang ZG, et al. Analysis of the relationship between polymorphism of angiotensin-converting enzyme gene and lung cancer [article in Chinese]. Zhongguo Fei Ai Za Zhi 2005; 8: 211–214. 12. Yaren A, Oztop I, Turgut S, et al. Angiotensin-converting enzyme gene polymorphism is associated with anemia in non small-cell lung cancer. Exp Biol Med (Maywood) 2008; 233: 32–37. 13. Nacak M, Nacak I, Sanli M, et al. Association of angiotensin converting enzyme gene insertion/deletion polymorphism with lung cancer in Turkey. Cancer Genet Cytogenet 2010; 198: 22–26. 14. Dević Pavlić S, Ristić S, Flego V, et al. Angiotensin converting enzyme insertion/deletion gene polymorphism in lung cancer patients. Genet Test Mol Biomarkers 2012; 16: 722–725. 15. Tahara T, Shibata T, Nakamura M, et al. Effect of polymorphisms in the 3’ untranslated region (3’-UTR) of vascular endothelial growth factor gene on gastric cancer and peptic ulcer diseases in Japan. Mol Carcinog 2009; 48: 1030–1037. 16. Röcken C, Lendeckel U, Dierkes J, et al. The number of lymph node metastases in gastric cancer correlates with the angiotensin I-converting enzyme gene insertion/deletion polymorphism. Clin Cancer Res 2005; 11: 2526–2530. 17. Gao M, Wang Y, Shi Y, et al. The relationship between three well-characterized polymorphisms of the angiotensin converting enzyme gene and lung cancer risk: A case-control study and a meta-analysis. J Renin Angiotensin Aldosterone Syst 2012; 13: 455–460. 18. Saijonmaa O, Nyman T and Fyhrquist F. Regulation of angiotensin-converting enzyme production by nicotine in human endothelial cells. Am J Physiol Heart Circ Physiol 2005; 289: 2000–2004. 19. Ljungberg L, Alehagen U, Länne T, et al. The association between circulating angiotensin-converting enzyme and cardiovascular risk in the elderly: A cross-sectional study. J Renin Angiotensin Aldosterone Syst 2011; 20: 1–9.
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research-article2014
JRA0010.1177/1470320314552310Journal of the Renin-Angiotensin-Aldosterone SystemWang et al.
Original Article
Angiotensin-converting enzyme insertion/ deletion gene polymorphism and lung cancer risk: A meta-analysis
Journal of the Renin-AngiotensinAldosterone System 2015, Vol. 16(1) 189–194 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1470320314552310 jra.sagepub.com
Nan Wang1, DaFu Yang1, Bin Ji1 and JianYou Li2
Abstract Objective: Angiotensin-converting enzyme (ACE) I/D polymorphism has been reported to be associated with lung cancer, but the results of previous studies are conflicting. The present study was designed to investigate the association between this polymorphism and the risk of lung cancer using a meta-analysis of the published studies. Methods: Two investigators independently searched the PubMed, Embase and CNKI databases. This meta-analysis covered six case-control studies, including 807 lung cancer patients and 816 healthy controls. Results: The results of this meta-analysis based on all the studies showed no significant association between ACE I/D gene polymorphism and lung cancer risk (DD vs II: OR = 1.18, 95% CI = 0.68–2.04; DI vs II: OR = 0.93, 95% CI = 0.56–1.53; DD+DI vs II: OR = 1.01, 95% CI = 0.68–1.50; DD vs II+DD: OR =1.11, 95% CI = 0.73–1.71). In the subgroup analysis by race and the larger studies (n > 200 participants), no significant associations between the ACE I/D polymorphism and risk of lung cancer were indicated. However, when the analyses were restricted to small studies (n ≤ 200 participants), a significantly higher risk was observed (DD vs II: OR = 2.57, 95% CI = 1.24–5.30). Conclusions: This meta-analysis suggests that the ACE gene I/D polymorphism may not be associated with the risk of lung cancer, and the observed increase in the risk of lung cancer may be due to small-study bias. Keywords ACE, gene polymorphism, lung cancer, meta-analysis Date received 21 December 2013; accepted 25 July 2014
Introduction According to the International Agency for Research on Cancer of the World Health Organization, lung cancer is the most common cancer in the world, with an estimated 1.6 million new cases in 2008, representing one in eight of all new cancer cases. It is also the most common form of cancer death in the world, comprising nearly one in five of all deaths from cancer.1 There are many factors contributing to lung cancer, of which environmental exposure, primarily to smoking, is the major risk factor. However, not all lung cancers are due to smoking, and increasing evidence for the association between genetic factors and identified lung cancer risk has been accumulated in hundreds of studies.2 Existing evidence has suggested that genetic factors also play an important role in the pathogenesis of lung cancer.3 Angiotensin-converting enzyme (ACE) is a zinc metallopeptidase that converts angiotensin I to angiotensin II (vasoconstrictor) and degrades bradykinin (vasodilator), regulating blood pressure and cardiovascular homeostasis.4 Approximately 90% of the physiologic conversion
of angiotensin I to angiotensin II takes place in the lungs. ACE in peripheral blood is thought to be identical to the lung enzyme and is proportional to blood oxygen concentration, suggesting that serum ACE activity is closely correlated with the enzyme concentration in the pulmonary tissue.5 ACE plasma levels depend on a 287 bp insertion/ deletion (I/D) polymorphism of the ACE gene located on chromosome 17q23.6 Homozygotes for the D allele have the highest ACE plasma levels, homozygotes for the I
1Medical
Department, Huzhou Traditional Chinese Medicine Hospital, People’s Republic of China 2Medical Department, Huzhou Central Hospital, People’s Republic of China Corresponding author: JianYou Li, Medical Department, Huzhou Central Hospital, 198 Hongqi Road, Huzhou 313000, People’s Republic of China. Email: [email protected]
Creative Commons CC-BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 License (http://www.creativecommons.org/licenses/by-nc/3.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (http://www.uk.sagepub.com/aboutus/openaccess.htm). Downloaded from jra.sagepub.com at MICHIGAN STATE UNIV on April 6, 2015
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allele have the lowest, and ID heterozygotes have intermediate levels. Over the past few years, many studies have shown that the ACE I/D polymorphism may be closely associated with the risk of cancer, including breast, gastric, and prostate cancer. In addition, though, several studies found an association between ACE I/D polymorphism and lung cancer while others did not, suggesting that it may serve as a possible risk factor for lung cancer. Meta-analysis can be a useful tool in the detection of associations that could otherwise remain unseen in studies with small sample sizes, especially studies evaluating rare allele frequency polymorphisms.7 This has recently become an important part of genetic research, mainly because it can reconcile previously conducted studies that gave inconsistent results. The present study investigated, by performing a meta-analysis, whether the ACE I/D polymorphism is associated with lung cancer risk.
Data extraction Data were independently extracted by two investigators (Nan Wang and JianYou Li), and a consensus was reached on all of the items. To ensure quality, the most recent and complete articles were chosen if a study was published more than once. First author, year of publication, country, nationality, number of patients and controls, gene polymorphisms and evidence of Hardy-Weinberg equilibrium (HWE) were documented. Any encountered discrepancies were adjudicated by a discussion and a 100% consensus was reached.
Statistical analysis
Literature databases including PubMed, Embase and China National Knowledge Infrastructure (CNKI) databases were searched for all articles on any association between ACE I/D polymorphism and the risk of lung cancer (last search update November 30, 2013). The search strategy was designed to identify all possible studies using the following keywords: “ACE I/D,” ”lung cancer,” “polymorphism,” “single nucleotide polymorphism” and “genetic polymorphism.” The search was not restricted by language, but all included studies had to be conducted on humans. Reference lists of previous reviews and meta-analyses were searched manually. Unpublished reports were not considered. If more than one article was published by the same author using the same case series, the study covering the greater number of individuals was included.
We assessed HWE in the controls for each study using the goodness-of-fit test (chi-square or Fisher exact test) and p < 0.05 was considered as significant disequilibrium. ORs were used as a measure of the association between the ACE I/D polymorphism and risk of lung cancer under a homozygote comparison (DD vs II), a heterozygote comparison (DI vs II), a dominant model (DD+DI vs II) and a recessive mode (DD vs II+DI) between groups.8 Both the Cochran’s Q statistic to test for heterogeneity and the I2 statistic to quantify the proportion of the total variation due to heterogeneity were calculated. A p value of more than the nominal level of 0.10 for the Q statistic indicated a lack of heterogeneity across studies, allowing for the use of a fixed-effects model; otherwise, the random-effects model was used. We examined the following study characteristics: ethnicity and study sample size (≤200 and >200 individuals). Sensitivity analysis was performed to assess the stability of the results. Publication bias was investigated with a funnel plot, which is the main graphical method of assessing bias. To supplement the funnel plot approach, the Begg’s test was adopted (p < 0.05 was considered statistically significant). Data analysis was performed using STATA version 12.0 (StataCorp LP, College Station, TX, USA).
Inclusion and exclusion criteria
Results
The studies included in the meta-analysis met all of the following inclusion criteria: (1) case-control studies conducted to evaluate the association between the ACE I/D polymorphism and the risk of lung cancer; (2) sufficient genotype data to calculate the odds ratios (ORs) and 95% confidence intervals (CIs); and (3) the paper clearly described the sources of cases and controls. Major exclusion criteria were as follows: (1) studies lacking case-control evaluation of the association between ACE I/D polymorphism and risk of lung cancer; (2) case reports, letters, reviews, meta-analyses and editorial articles; (3) studies based on incomplete raw data or for which no usable data were reported; and (4) duplicate studies.
Study characteristics
Materials and methods Literature search strategy
A total of 151 articles were gleaned by a literature search of PubMed, Embase and CNKI databases, using different combinations of key terms. As shown in Figure 1, a final total of six case-control studies met our inclusion criteria,9–14 including 807 cases and 816 controls. The genotype distributions in the controls of all studies were in agreement with HWE. There were three studies of Europeans12–14 and three of Asians.9–11 The information from these six studies and the numbers of cases and controls with II, DI and DD genotypes reported in each study are all presented in Table 1.
Downloaded from jra.sagepub.com at MICHIGAN STATE UNIV on April 6, 2015
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Figure 1. Flow diagram of the study search and selection process.
CNKI: China National Knowledge Infrastructure; ACE: angiotensin-converting enzyme; I: insertion; D: deletion.
Table 1. Characteristics of the included studies for meta-analysis. Study included
Year
Area
Ethnicity
Cases/ Controls
Cheon et al.9 Wang et al.10 Zhang et al.11 Yaren et al.12 Nacak et al.13 Dević Pavlić et al.14
2000 2000 2005 2008 2010 2012
Korea China China Turkey Turkey Croatia
Asian Asian Asian Caucasian Caucasian Caucasian
218/121 34/38 47/54 75/85 125/165 308/353
Genotypes for cases
Genotypes for controls
HWE test
II DI DD
II DI DD
72 116 30 10 6 18 21 21 5 4 39 32 37 50 38 64 148 96
48 50 23 13 18 7 20 30 4 14 37 34 29 72 64 78 177 98
0.13 0.86 0.11 0.47 0.27 0.91
HWE: Hardy-Weinberg equilibrium.
Quantitative synthesis The evaluation of an association between the ACE I/D polymorphism and the risk of lung cancer is displayed in Table 2. The results of this meta-analysis showed no significant association between the ACE I/D polymorphism and lung cancer risk in any of the genetic models (Figure 2, DD vs II: OR = 1.18, 95% CI = 0.68–2.04; DI vs II: OR = 0.93, 95% CI = 0.56–1.53; DD+DI vs II: OR = 1.01, 95% CI = 0.68–1.50; DD vs II+DI: OR = 1.11, 95% CI = 0.73– 1.71). In a subgroup analysis by ethnicity, the studies included were divided into Asian and Caucasian populations, and no significant association was found between the ACE I/D polymorphism and lung cancer risk in Asians (DD vs II: OR = 1.20, 95% CI = 0.71–2.03; DI vs II: OR = 0.76, 95% CI = 0.30–1.92; DD+DI vs II: OR = 1.07, 95% CI = 0.74–1.54; DD vs II+DI: OR = 1.64, 95% CI = 0.45– 6.01) and in Caucasians (DD vs II: OR = 1.09, 95% CI = 0.45–2.66; DI vs II: OR = 1.08, 95% CI = 0.50–2.35; DD+DI vs II: OR = 1.08, 95% CI = 0.50–2.42; DD vs
II+DI: OR = 1.01, 95% CI = 0.79–1.30). However, when the analyses were restricted to three small studies (n ≤ 200 participants), meta-analysis results showed a significant association with the risk of lung cancer (DD vs II: OR = 2.57, 95% CI = 1.24–5.30). Sensitivity analyses were conducted by altering the statistic models. No material alteration was detected, indicating that our results were statistically robust (DD vs II: OR = 1.05, 95% CI = 0.79– 1.39; DI vs II: OR = 0.97, 95% CI = 0.77–1.26; DD+DI vs II: OR = 1.00, 95% CI = 0.79–1.26; DD vs II+DI: OR = 1.05, 95% CI = 0.84–1.31).
Publication bias The publication bias of the meta-analysis of the association between the ACE I/D polymorphism and lung cancer risk was detected by Begg’s funnel plot; all graphical funnel plots of the included studies appeared to be symmetrical. Results showed that there was no publication bias (DD vs II: Begg’s test, p = 1.00, Egger test; DI vs II: Begg’s
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Table 2. Stratified analyses of the ACE I/D polymorphism and risk of lung cancer. Variables
Cases/ controls
DD vs II
DI vs II
DD+DI vs II
DD vs II+DI
OR (95% CI) p
OR (95% CI) p
OR (95% CI) p
OR (95% CI) p
6
807/816
1.18 (0.68–2.04) 0.02
0.93 (0.56–1.53) 0.01
1.01 (0.68–1.50) 0.04
3 3
299/213 508/603
1.20 (0.71–2.03) 0.16 1.09 (0.45–2.66) 0.01
0.76 (0.30–1.92) 0.02 1.08 (0.50–2.35) 0.02
1.07 (0.74–1.54) 0.57 1.08 (0.50–2.42) 0.01
3 3
651/639 156/177
0.81 (0.46–1.42) 0.05 2.57 (1.24–5.30) 0.49
0.98 (0.58–1.65) 0.03 0.89 (0.24–3.31) 0.01
0.89 (0.56–1.42) 0.05 1.36 (0.57–3.26) 0.09
1.11 (0.73–1.71) 0.02 1.64 (0.45–6.01) 0.01 1.01 (0.79–1.30) 0.20 0.86 (0.58–1.29) 0.11 1.94 (0.74–5.09) 0.06
N
Total Ethnicity Asian Caucasian Sample size >200 ≤200
N = number of comparisons; p value of the Q-test for heterogeneity test. Random-effects model was used when p value for heterogeneity test 0.05, Figure 3).
Discussion Genetic polymorphisms that alter the amount of protein expressed may have a substantial influence on disease activity.15 Lung cancer is a complex disease, and many factors, including environmental and occupational exposure, cigarette smoking, and genetics, contribute to its progression. The I/D polymorphism accounts for 20% to 50% of the variance in ACE expression or activity in blood and tissues among individuals.16 The relationship between ACE I/D polymorphism and risk of lung cancer has been addressed in several studies, and the results are controversial. An apparent discrepancy in the results may be due to ethnic differences, or to insufficient sample size. The aim of meta-analysis is to combine the same kinds of studies to increase the sample size and statistical power, thereby producing more authentic results. This is the first meta-analysis to consider ACE I/D polymorphism and the risk of lung cancer. In the current metaanalysis, the association between ACE I/D polymorphism and the risk of lung cancer was examined by critically including all published studies. Ultimately, only six case-control studies were included, comprising a total of 807 patients and 816 healthy controls. The final results of this meta-analysis did not show any significant association between ACE I/D polymorphism and the risk of lung cancer. Because results may be affected by ethnicity, a race-related subgroup analysis was performed, and no significant association was found
between ACE I/D polymorphism and susceptibility to lung cancer in either Caucasian or Asian populations. When stratifying by sample size (≤200), this meta-analysis detected a significant association between ACE I/D polymorphism and lung cancer. However, this conclusion was drawn using a small number of samples, which suggests that the observed associations between ACE I/D polymorphism and an increased lung cancer risk reflect chance observations rather than true associations, which is a small-study bias. Further sensitivity analysis confirmed the significance of the association between ACE I/D polymorphism and risk of lung cancer. No evidence collected in this meta-analysis indicated publication bias (p > 0.05). The potential influence of ACE I/D polymorphism may be affected by gene-gene and gene-environment interactions. The effects of ACE I/D polymorphism on lung cancer may be attributable to linkage disequilibrium with the ACE gene A-240T and A2350G polymorphisms.17 In addition, nicotine and its metabolites increase the expression and activity of ACE in human endothelial cells,18 and higher levels of circulating ACE, which are associated with the ACE I/D polymorphism, are found in male smokers.19 This suggests that the ACE I/D polymorphism may be correlated with tobacco smoking and with an increased risk of lung cancer development. However, one study could not be included in this meta-analysis, and further studies of genegene and gene-environment interactions must be taken into consideration for assessment of the risk of lung cancer. The current meta-analysis has some limitations in this meta-analysis: 1) Only published studies were included, so publication bias may be an issue, even though the use of a
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statistical test did not indicate any; 2) because of incomplete raw data or publication limitations, some relevant studies could not be included in our analysis; and 3) genegene and gene-environment interactions were not tested in the present study because of the lack of information from the original studies. In conclusion, this meta-analysis indicates that the ACE I/D polymorphism may be not associated with lung cancer risk, and the observed increase in the risk of lung cancer may be due to small-study bias. Because few studies are available in this field and because current evidence remains limited, large studies of adequate methodological quality, properly controlling for possible confounding factors, are greatly needed. Acknowledgement We thank LetPub (www.letpub.com) for its linguistic assistance.
Conflict of interest None declared.
Funding This work was supported by a grant from Zhejiang Science and Technology R&D Fund (2014C33245), the Medical Scientific Research Foundation of Zhejiang Province (2012RCB039), and the Huzhou Science and Technology R&D Fund (2012YS02).
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