Background
Non-small cell lung cancer (NSCLC) accounts for 89% of all lung cancer, and 30% of NSCLC patients present with locally-advanced unresectable tumors (unresectable stage IIIa and IIIb) [
1]. Radiotherapy combined with chemotherapy, either sequentially or concurrently, is the standard treatment regimen for these patients, which, however, have resulted in unsatisfactory prognosis, with a 5-year survival rate of about 10-15% [
1], and a median survival time (MST) of 16-18 months [
2,
3]. There has been a persistent interest in search for readily accessible molecular markers that may provide therapeutic benefits by predicting clinical outcomes of these locally advanced NSCLC (LA-NSCLC) on an individual basis.
Angiogenesis is an essential process in the development, growth, and metastasis of malignant tumors including lung cancer [
4]. Vascular endothelial growth factor (VEGF) is one of the most potent and predominant mediators of angiogenesis, which stimulate vascular endothelial cell growth, survival, and proliferation. Recent investigation has further revealed that VEGF acts as a mitogenic and survival signal for the tumor cell itself, indicating a broader range of tumor-promoting effects. Therefore, VEGF stands as a good candidate for prognostic biomarkers in cancer patients. Indeed, most tumors produce VEGF, whereas inhibition of the VEGF signaling significantly inhibits tumor growth
in vivo [
5]. In NSCLC, it has been found that a high expression of VEGF protein or mRNA was associated with increased tumor angiogenesis, early tumor relapse and reduced survival time [
6‐
8]. A recent report further linked some functional
VEGF polymorphisms with prognosis of early stage (stage I and II) NSCLC, probably through regulation of VEGF expression [
9]. However, LA-NSCLC accounts for a significant proportion of lung cancer, and it is not known if
VEGF polymorphisms are associated with prognosis within this particular population.
Previous studies primarily focused on three common functional single nucleotide polymorphisms of the
VEGF gene, including the -460 T > C, -634 G > C (also assigned as +405 G > C) and +936 C > T (minor allele frequency = 0.422, 0.431 and 0.222 in Caucasians, respectively, according to the Hapmap database). The -460 T > C SNP is located in the promoter region and may influence the promoter activity [
10]; the -634 G > C SNP lies within the 5'-untranslated region and may affect the transcriptional factor binding affinity [
11]; the +936 C > T SNP is located in the 3'-untranslated region and has been associated with lower VEGF plasma levels [
12]. In the present study, we evaluated the association of these three potentially functional
VEGF SNPs (i.e., -460 T > C, -634 G > C [also assigned as +405 G > C] and +936 C > T) with overall survival (OS) of LA-NSCLC patients.
Discussion
Several studies have reported the association between
VEGF polymorphisms and progress and survival of different cancers [
16‐
19], but no study has investigated the association between the
VEGF polymorphisms and LA-NSCLC patients' survival to date. To reduce confounding effects of clinical parameters on the association, we limited our study subjects to a group of 124 Caucasian patients with homogenous stage IIIa and IIIb NSCLC, who received well-documented definitive chemoradiotherapy as previously described [
13]. We found that the
VEGF - 460 C variant genotypes were associated with a significantly improved OS, compared with the
VEGF -460 TT genotype.
To give a comprehensive view of the association between
VEGF genotypes and the prognosis of different cancer types, we summarized the published data in Table
3. Most of these studies confirmed an influence of
VEGF SNPs on the overall survival of cancer patients. However, these studies differed substantially in their conclusions. Even for the same
VEGF SNP, different risk allele was reported. Different ethnic populations might be one rational reason for the inconsistent results. Another possible explanation may be that the effects of VEGF are tumor-specific. The interaction of different therapeutic strategies with
VEGF genotypes may also contribute to the diverse clinical outcomes. In NSCLC, the three studies (including ours) were not consistent in the
VEGF risk alleles, suggesting that a further investigation was warranted. For example, Masago
et al. reported an association between -460 C allele and a poorer survival of advanced NSCLC in Japanese patients [
20], which was opposite to our findings in Caucasian patients. Numerous factors could have played a role in the ethnic discrepancy, including gene-gene interaction from different genetic background and gene-environmental interaction from different lifestyles. Even in the same ethnicity of Caucasians, the study by Heist
et al. failed to find any significant association between -460 C allele and survival in 462 early-stage NSCLC patients, most of whom were surgically resected [
9]. In that study, there were only 32 patients (7%) receiving radiation and three patients (0.6%) treated with chemotherapy. In contrast, the 124 LA-NSCLC patients of current study all received radiotherapy, and carriers of the C allele of -460 T > C polymorphism were found to benefit from radiotherapy. These findings, once validated in larger studies, will guide tailored therapeutics for individual patients.
Table 3
Summary of the influence of VEGF SNPs on cancer OS
Guan (Current) | 2010 | LA-NSCLC | USA | Caucasian | -460T > C, -634G > C, and 936C > T | 124 | T for -460T > C |
| 2009 | Head&neck | France | Caucasian | -460T > C, -634G > C, and 936C > T | 49 | None |
| 2009 | Advanced NSCLC | Japan | Asian | -460T > C, -1154G > A, -2578C > A, 405G > C, and 936C > T | 126 | C for -460T > C, A for -1154G > A, and A for -2578C > A |
| 2009 | Colorectum | Greece | Caucasian | -460T > C, -634G > C, -1154G > A, -2578C > A, and 936C > T | 312 | T for -460T > C, G for -634G > C, C for -2578C > A, and C for 936C > T |
| 2009 | Esophagus | Canada | Caucasian | -460T > C, 405G > C, and 936C > T | 361 | C for 936C > T |
| 2008 | Early NSCLC | USA | Caucasian | -460T > C, 405G > C, and 936C > T | 462 | G for 405G > C and C for 936C > T |
| 2008 | Colorectum | Korea | Asian | -634G > C, -2578C > A, and 936C > T | 445 | G for -634G > C and T for 936C > T |
| 2007 | Stomach | Korea | Asian | -116G > A, -460T > C, 405G > C, and 936C > T | 503 | C for -460T > C and T for 936C > T |
| 2007 | Renal cell | Japan | Asian | -634G > C, -2578C > A, and -1154G > A | 213 | C for -2578C > A |
| 2007 | Ovarian | Austria | Caucasian | -634G > C, -1154G > A, and -2578C > A | 563 | None |
| 2006 | Stomach | Greece | Caucasian | -634G > C, -2578C > A, -1154G > A, and 936C > T | 100 | C for -634G > C |
| 2005 | Breast | China | Asian | -460T > C, 405G > C, and 936C > T | 1119 | C for -460T > C, and G for 405G > C |
It is not clear how the
VEGF -460 C allele contributes to a better survival in LA-NSCLC patients. A previous
in vitro study indicated that the T allele of the
VEGF -460 T > C polymorphism located in the promoter of the
VEGF gene was associated with a decreased
VEGF promoter activity [
10]. Hence, the
VEGF -460 C allele may be associated with an increased VEGF expression, which would promote tumor angiogenesis. However, the majority of NSCLC patients included in the current study received chemotherapy in addition to radiotherapy (112 out of 124). It is possible that the increased tumor vasculature may enhance radiotherapy efficacy through inhibiting tumor radioresistance from radiation-induced hypoxia, or facilitate the delivery of chemotherapeutic agents to the tumor site and may have led to enhanced synergistic effect with radiotherapy. Or, the
VEGF -460 C allele has some additional unknown biological functions, besides regulation of mRNA expression. Further mechanistic studies are required to clarify this issue.
The strength of this study is that we included patients with stage IIIa and IIIb only, who received radiotherapy mostly in the range of 60-70 Gy with detailed OS data. However, there are several limitations. First, the study could not address the mechanism of how the
VEGF polymorphisms influence the survival outcomes of lung cancer patients. Previous study demonstrated a good correlation between TC/CC genotypes of the
VEGF -460 T > C polymorphism and increased serum VEGF levels in colorectal cancer patients [
21]. An increased serum VEGF expression was also observed in ovarian cancer patients carrying -634 C allele [
22]. We are collecting related data to determine if there is such correlation between the
VEGF polymorphisms and the VEGF protein levels in NSCLC patients. Secondly, we only included three common functional, promoter
VEGF SNPs, which is far from comprehensive. Indeed, the
VEGF gene is highly polymorphic with at least 140 variants reported to date
http://www.ncbi.nlm.nih.gov/SNP/. Some important functional SNPs may be missed or the observed association may result from genetic linkages with other untyped SNPs. Thirdly, our sample size is not big enough to allow evaluation of interactions between the studied polymorphisms and dose of radiation therapy. For the same reason, there appeared a wide confidence interval in our stratified analyses by tumor stage and the significance was lost due to the reduced statistical power. Therefore, a complete investigation of tagging SNPs in larger samples may be necessary in future studies.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
XXG, QYW, and ZXL designed the study. XXG, ZSL and XLY performed the experiments. XXG, MY, and HZ analyzed the data. XXG and MY wrote the manuscript. LEW, MSO, and RK coordinated the data and helped to revise the manuscript. All authors read and approved the final manuscript.