Association of an EGFR intron 1 SNP with never-smoking female lung adenocarcinoma patients

Abstract

Epidermal growth factor receptor (EGFR) plays an important role in the development and progression of a variety of malignant tumors. To test single nucleotide polymorphisms (SNPs) and haplotypes of the EGFR in modulating the lung cancer susceptibility, we conducted a matched case–control study of 730 lung cancer patients and 730 healthy controls for examining the association in Taiwanese population. Fourteen tag SNPs distributed in EGFR were selected for genotyping and one SNP 8227G>A (rs763317) located in the intron 1 of EGFR was significantly associated with lung cancer (P = 0.009). Interestingly, the increase of lung cancer risk is significantly associated with never-smoking female adenocarcinoma patients harboring 8227A allele. In never-smoking female population, ORs for 8227G>A were significantly increased in adenocarcinoma subtype (adjusted odds ratio (OR) for GA genotype = 1.23, 95% confidence interval (CI) = 0.87–1.75; and adjusted OR for AA genotype = 3.52, 95% CI = 1.32–9.37, respectively). The ORs in dominant or recessive genetic model were also significantly increased in female lung adenocarcinoma subtype (adjusted OR = 1.35, 95% CI = 1.05–1.90; and adjusted OR = 3.26, 95% CI = 1.24–8.62, respectively). Haplotype analyses of 14 EGFR SNPs revealed that haplotype comprising the rare allele of 8227G>A and the common allele of the other 13 SNPs was associated with a significantly increased risk of female adenocarcinoma (OR = 2.81, 95% CI = 1.02–7.77). Together, our results suggest that polymorphisms or haplotypes of the EGFR play an important role in the development of lung cancer in Taiwan, particularly in never-smoking female lung adenocarcinoma.

Introduction

Lung cancer is the leading cause of cancer mortality worldwide and in Taiwan [1]. Although cigarette smoking is known to be the most important risk factor and a number of smoking-related genetic alterations have been identified to be responsible for lung tumorigenesis such as mutations in K-ras[2], only a fraction of smokers develop lung cancer during their lifetime suggesting that other genetic and epigenetic factors are of importance in determining individual's susceptibility to lung cancer [3], [4]. In Taiwan, less than 10% of Taiwanese female with lung cancer smoke and overall only around 50% of lung cancer incidence can be attributed with cigarette smoking [5]. Adenocarcinoma is the major pathological tissue type of lung cancer in female. Furthermore, the lung cancer mortality in Taiwan was shown to have gender disparity with a male-to-female ratio of around 2.0 lower than that of other areas of the world [6]. These results suggest that different molecular mechanisms may be involved in lung tumorigenesis in Taiwan.

Studies of tumorigenesis of lung cancers have shown that the epidermal growth factor receptor (EGFR), the first receptor protein tyrosine kinase described, plays a critical role in the signal transduction pathway for cell proliferation, differentiation, migration, motility, resistance to apoptosis and enhance cell survival [7]. Consistent with these finding at the cellular level, somatic aberrations such as over-expression, mutation, amplification, or deregulation of EGFR are associated with many malignant tumors including lung cancer and used as molecular target for chemotherapy [8], [9]. It is therefore important to explore the genetic variations in EGFR for determining the susceptibility of developing lung cancer. To date, several polymorphisms in EGFR gene are well described and associated with increased EGFR protein production. For example, CA simple sequence repeat 1 (CA-SSR1) in intron 1 is a highly polymorphic dinucleotide locus and the lower number of repeats was correlated with increased transcription and expression of EGFR[10], [11], [12]. Two single nucleotide polymorphisms (SNPs) in the promoter region, 216 (G/T or T/T) and 191 (C/A or A/A) were correlated with promoter activity and expression of EGFR [12], [13], [14]. In addition, a polymorphism (G2607A) in EGFR tyrosine kinase domain was identified to be associated with risk of lung cancer [15]. Given the various consequences of EGFR aberrations in tumorigenesis of lung cancer influenced by status of smoke exposure, ethnicity and gender [16], we hypothesized that individual genetic susceptibility might be relevant for lung cancer tumorigenesis.

To investigate common polymorphisms and haplotypes of EGFR in association with lung cancer, we conducted a matched case–control study to examine the frequency distributions of genotypes and haplotype structures by using the known common tag SNPs distributed in EGFR between lung cancer patients and healthy controls in Taiwanese population. Interestingly, a common tag SNP 8227G>A located in intron 1 of EGFR was significantly associated with lung cancer, especially in never-smoking female lung adenocarcinoma patients.