Early onset lung cancer, cigarette smoking and the SNP309 of the murine double minute-2 (<it>MDM2</it>) gene

1471-2407-8-113 1471-2407 Research article Early onset lung cancer, cigarette smoking and the SNP309 of the murine double minute-2 (<it>MDM2</it>) gene Mittelstrass Kirstin kirstin.mittelstrass@helmholtz-muenchen.de Sauter Wiebke wiebke.sauter@helmholtz-muenchen.de Rosenberger Albert arosenb@gwdg.de Illig Thomas illig@helmholtz-muenchen.de Timofeeva Maria m.timofeeva@dkfz-heidelberg.de Klopp Norman klopp@helmholtz-muenchen.de Dienemann Hendrik hendrik.dienemann@thoraxklinik-heidelberg.de Meese Eckart hgemee@med-rz.uni-sb.de Sybrecht Gerhard prof.g.w.sybrecht@uniklinikum-saarland.de Woelke Gabi woelke@helmholtz-muenchen.de Cebulla Mathias mathias.cebulla@sanktgeorg.de Degen Maria maria.degen@t-online.de Morr Harald harald.morr.waldhof@t-online.de Drings Peter peter.drings@thoraxklinik-heidelberg.de Groeschel Andreas inagro@med-rz.uni-sb.de Kreymborg Grosse Karsten karsten.g.kreymborg@medizin.uni-leipzig.de Haeußinger Karl gauting@asklepios.com Hoeffken Gerd hoeffken@fachkrankenhasu-coswig.de Schmidt Christine schmidt@fachkrnakenhaus-coswig.de Jilge Bettina b.jilge@skc.de Schmidt Wilhelm e.schmidt@skc.de Ko You-Dschun y.ko@jk-bonn.de Taeuscher Dagmar d.taeuscher@t-online.de Chang-Claude Jenny j.chang-claude@dkfz-heidelberg.de Wichmann Heinz-Erich wichmann@helmholtz-muenchen.de Bickeboeller Heike hbickeb@gwdg.de Risch Angela a.risch@dkfz-heidelberg.de

Helmholtz Center Munich, German Research Center for Environmental Health, Institute of Epidemiology, Munich/Neuherberg, Germany

Department of Genetic Epidemiology, Georg-August University of Göttingen, Medical School, Göttingen, Germany

German Cancer Research Centre (DKFZ), Heidelberg, Germany

Thoraxklinik Heidelberg GmbH, Heidelberg, Germany

Institute of Human Genetics, University of the Saarland, Germany

Institute of Internal Medicine V, Medical School, University of the Saarland, Germany

Municipal Hospital „Sankt Georg", Leipzig, Germany

Clinic of Pneumology, Waldhof Elgershausen, Greifenstein, Germany

Department Internal Medicine-Oncology, Thorax-Clinic Heidelberg GmbH, Heidelberg, Germany

Centre for Internal Medicine, University Hospital Leipzig, Germany

Clinic of Pneumology München-Gauting, Munich, Germany

Clinic Coswig GmbH, Division Internal Medicine, Coswig, Germany

Chemnitz Hospital, Clinic for Internal Medicine, Chemnitz, Germany

Department of Oncology, University Hospital of Bonn, Germany

Wald-Hospital Gera GmbH, II. Medical Clinic, Gera, Germany

Ludwig-Maximilians-University of Munich, Institute of Medical Data Management, Biometrics and Epidemiology, Germany

BMC Cancer 1471-2407 2008 8 1 113 http://www.biomedcentral.com/1471-2407/8/113 18433484 10.1186/1471-2407-8-113 19 9 2007 23 4 2008 23 4 2008 2008 Mittelstrass et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The polymorphism SNP309 (rs2279744) in the promoter region of the MDM2 gene has been shown to alter protein expression and may play a role in the susceptibility to lung cancer. The MDM2 protein is a key inhibitor of p53 and several mechanisms of MDM2/p53 interactions are presently known: modulating DNA-repair, cell-cycle control, cell growth and apoptosis.

We used 635 Caucasian patients diagnosed with lung cancer before 51 years of age and 1300 healthy gender and age frequency matched population Caucasian controls to investigate the association between the MDM2 SNP309 and the risk of developing early onset lung cancer. Conditional logistic models were applied to assess the genotype-phenotype association, adjusted for smoking.

Compared to the GG genotype, the adjusted ORs for the TG and TT genotype were 0.9 (95% CI: 0.7–1.5) and 1.0 (95% CI: 0.7–1.5), respectively. Also no association was found for histological subtypes of lung cancer. The strength of this study is that within young cases the genetic component to develop lung cancer may be greater. Our results indicate that the MDM2 SNP309 is not significantly associated with lung carcinogenesis but point towards gender-specific differences.

Background

Human cells have developed a complex system to protect themselves from genotoxic damage where the p53 tumor suppressor gene plays an important role in protecting against such insults by serving as an integrator of the signals produced by DNA damage. The MDM2 protein inhibits p53 transactivation activity and promotes its export from the nucleus by binding to the transcriptional activation domain of p53 1 and acts as an ubiquitin ligase upon p53 pushing fast degradation of the suppressor 23.

Recently, a SNP (SNP309, G2580T) at the intronic p53-response promoter of MDM2 was identified and associated with altered Sp1 binding affinity and expression levels of MDM2 RNA and protein 4. Contradictory results were reported regarding the MDM2 SNP309 association with lung cancer 5678. In addition the polymorphism was correlated with a decreased age at the time of lung cancer diagnosis in Li-Fraumeni syndrome and sporadic sarcoma patients 4. Our study is the first report on a large German case-control study of young lung cancer patients (age of onset < 51 years) investigating the MDM2 SNP 309.

Methods

Study population

The study population consists of 635 lung cancer patients with an onset of disease ≤ 50 years of age and 1300 healthy population controls, all Caucasians. Controls were recruited from the KORA S3 + S4 (Cooperative Health Research in the Augsburg Region) surveys, which are large population-based consecutive cross-sectional studies 910 and matched by gender and 3-years age groups to cases in a 1:2 matching design. In order to increase the sample size of early onset lung cancer patients we included cases from two existing studies. 472 cases were from the LUCY (

LUng

Cancer in the

Young) study. Additional 163 cases were derived from the hospital-based

Heidelberg

Lung

Cancer (HLC) study from the Thoraxklinik Heidelberg 11.

The LUCY-study is a multicenter study with 31 participating clinics all over Germany. Only newly diagnosed patients with histological or cytological confirmed primary lung cancer entered the study. Detailed epidemiologic data on family history, tobacco and smoking exposure, education and occupational exposure have been collected and blood samples were taken.

The HLC-study is an ongoing hospital based case-control study. The DKFZ has recruited over 1000 LC cases at and in collaboration with the Thoraxklinik Heidelberg. 163 of these LC cases with onset of disease under age 51, recruited between 01/1997 and 12/2003 were included in the analysis. Data on occupational exposure, tobacco smoking and educational status were assessed by a self-administered questionnaire.

The KORA-study is a population based epidemiological survey of persons living in or near the city of Augsburg, Southern Germany conducted since 1984. No major population stratification between KORA (Southwest Germany) and two other cohorts from Northern Germany could be detected in an intensive study using a genomic control approach 12.

Informed consent was obtained from all study participants and the studies were approved by the ethical committee of the Bayerische Landesärztekammer, the corresponding local ethics committees of the participating clinics and the ethical committee of the University of Heidelberg.

Genotyping

The detection of the MDM2 gene polymorphism (rs2279744; G > T; NM_002392.2) was based upon analysis of primer extension products generated from previously amplified genomic DNA using a chip-based MALDI-TOF (matrix-assisted laser desorption/ionization time-of flight) mass spectrometry platform (SEQUENOM, Inc., San Diego, CA) as described in Weidinger et al. (2004) 13. Genotyping was performed by laboratory personnel blinded to case-control status. Standard genotyping quality control included 10% duplicate samples, negative and positive samples and checking for Hardy-Weinberg equilibrium (HWE).

Statistical analysis

Hardy Weinberg Equilibrium (HWE) was tested using a log-likelihood test. Conditional logistic regression models were applied to test for a genotype-phenotype association and gene-smoking interaction, with conditioning on the matched variables age groups (≤ 40 years, 41–45 years, 46–50 years) and gender. The amount of smoking exposure (s. table 1 for definition) was considered as a covariate to adjust for a smoking-related increase in lung cancer risk. The overall level of significance was set to 5%. We investigated differences between multiple characteristics (age of onset, gender, LC subtype and MDM2 SNP390 genotype) of both cases-samples by calculating a propensity score, which is defined as the conditional probability of assignment to a particular case-sample given a vector of observed covariates 14. We then calculated kappa as measurement of agreement between true and the assigned membership to a case-sample and performed a McNemar's test for agreement between these.

Table 1

Characteristics of lung cancer cases and healthy controls

Category

Group

Cases (n = 635)

Controls

LUCY-study

(n = 472)

HLC-study

(n = 163)

KORA-study

(n = 1300)

gender

men

66% (310)

59% (96)

63% (819)

women

34% (162)

41% (67)

37% (481)

age at diagnosis (mean ± SD)

men

45.4 ± 4.1

45.4 ± 3.7

45.2 ± 4.3

women

44.5 ± 4.6

45.1 ± 4.6

44.7 ± 4.7

age at diagnosis (men)

≤ 40 years

13% (40)

11% (11)

14% (116)

41–45 years

32% (99)

33% (32)

31% (251)

46–50 years

55% (171)

55% (53)

55% (451)

age at diagnosis (women)

≤ 40 years

17% (28)

16% (11)

17% (83)

41–45 years

31% (51)

25% (17)

30% (144)

46–50 years

51% (83)

58% (39)

53% (255)

LC subtypes (men)

NSCLC-Adenocarcinoma

26% (81)

35% (34)

other NSCLC

40% (125)

43% (41)

SCLC

26% (81)

20% (19)

other types

7% (22)

2% (2)

LC subtypes (women)

NSCLC-Adenocarcinoma

44% (71)

54% (36)

other NSCLC

22% (36)

24% (16)

SCLC

25% (41)

16% (11)

other types

9% (14)

6% (4)

smoking exposure (packyears)

minimally exposed (0–10)

12% (57)

13% (21)

54% (712)

lightly exposed (11–20)

17% (81)

8% (13)

14% (178)

moderately exposed (21–30)

31% (144)

20% (33)

15% (188)

highly exposed (31++)

39% (186)

52% (85)

15% (192)

unknown

0.9% (4)

7% (11)

2% (30)

MDM2 SNP309 genotypes*

42% (199)

44% (71)

42% (547)

47% (222)

44% (71)

46% (598)

10% (49)

13% (21)

12% (149)

unknown

0.3% (2)

0.5% (6)

mean age at diagnosis (95% CI)

45.1 (44.5–45.7)

44.8 (43.7–45.8)

45.3 (44.7–45.8)

45.6 (44.7–46.5)

44.6 (43.3–45.9)

45.9 (44.2–47.6)

LUCY-study: Lung Cancer in the Young study; HLC-Study: Heidelberg lung cancer study; Other NSCLC = other non small cell lung cancers (NSCLC excluding adenocarcinoma), SCLC = small cell lung cancer, other types = other kinds of lung cancer

All analyses were performed with SAS 9.1^®. Power analyses for the single marker association was done according to the method of Slager 2001 15 and for the single marker interaction tests it was accomplished by using Nquery Advisor 4.0.

Results

Population characteristics

There was no statistically significant difference in the distribution of gender (p = 0.13) and age (p = 0.80) between patients and controls. The distribution of the histology subtypes within the cases can be seen in table 1. Although one might see a higher percentage of NSCLC-Adenocarcinoma within HCL-cases, the difference between both case-populations was by far not significant (p = 0.617). In total, there are no major differences between both case-populations. Applying the propensity score approach we found no agreement between the true and the assigned membership to a case-sample (kappa 0.01; 95% CI: -0.1 to 0.1). Thus we have no evidence to assume group differences shown by the multiple characteristics considered (p = 1.00).

Genotyping

The genotyping success rates were above 99.5%. No discordance between the duplicates was found.

Associations of the MDM2 SNP309 with lung cancer

No deviations from HWE were found in the genotype distribution of the MDM2 polymorphism among controls (p = 0.453) or cases (p = 0.474). All but eight samples were successfully genotyped for the MDM2 SNP309. The minor allele frequency (MAF) was 0.34 (CI: 0.35–0.33). Lung cancer was not found to be associated with the MDM2 SNP309 (p = 0.988). Compared to the GG genotype, the smoking adjusted ORs for the TG and TT genotypes were 1.0 (95% CI: 0.7–1.5) and 1.0 (95% CI: 0.7–1.5), respectively. Both case populations compared separately to the controls showed no significant associations (Table 2). Gender related subgroup analysis yielded no association of the MDM2 SNP309 and lung cancer (Table 2, 3, 4). Also no influence in lung cancer risk by the MDM2 SNP309 was observed for the diverse histological subtypes of lung cancer (Table 3, 4, 5).

Table 2

Association of MDM2 SNP309 with lung cancer within both case-populations

genotype

95% CI

p-value

LUCY cases (n = 470) vs. KORA controls (n = 815)

TG vs. GG

1.1^§

0.7–1.6

0.794

TT vs. GG

1.0^§

0.7–1.6

0.841

men: LUCY cases (n = 309) vs. KORA controls (n = 815)

TG vs. GG

1.1^§§

0.7–1.8

0.706

TT vs. GG

1.1^§§

0.7–1.8

0.751

women: LUCY cases (n = 161) vs. KORA controls (n = 815)

TG vs. GG

1.0^§§

0.5–2.1

0.937

TT vs. GG

1.0^§§

0.5–2.1

0.966

gender difference in genotypic ORs

0.778

HLC cases (n = 163) vs. KORA controls (n = 479)

TG vs. GG

0.9^§

0.5–1.7

0.761

TT vs. GG

1.0^§

0.5–1.7

0.906

men: HLC cases (n = 96) vs. KORA controls (n = 479)

TG vs. GG

1.2^§§

0.5–3.0

0.648

TT vs. GG

1.6^§§

0.7–3.7

0.314

women: HLC cases (n = 67) vs. KORA controls (n = 479)

TG vs. GG

0.7^§§

0.3–1.6

0.372

TT vs. GG

0.5^§§

0.2–1.3

0.159

gender difference in genotypic ORs

0.083

HLC cases vs. LUCY cases (distribution of TT/TG/GG)

all

^$0.773

men

^$0.383

women

^$0.100

^§conditional to age/gender-strata (6 groups) and adjusted for smoking exposure^§§conditional to age-strata (3 groups) and adjusted for smoking exposure and gender^$. Fishers Exact Test

Table 3

Association of MDM2 SNP309 with lung cancer

gender

Genotype

95% CI

p-value

men*

TG vs. GG

1.1

0.7 – 2.0

0.630

men*

TT vs. GG

1.2

0.7 – 2.2

0.504

women*

TG vs. GG

0.9

0.5 – 1.6

0.723

women*

TT vs. GG

0.8

0.5 – 1.3

0.565

histology

NSCLC-Adenocarcinoma**

TG vs. GG

1.0

0.6 – 1.7

0.991

NSCLC-Adenocarcinoma**

TT vs. GG

1.0

0.6 – 1.8

0.890

other NSCLC**

TG vs. GG

1.0

0.6 – 1.8

0.873

other NSCLC**

TT vs. GG

0.9

0.5 – 1.6

0.751

SCLC**

TG vs. GG

1.0

0.5 – 1.9

0.980

SCLC**

TT vs. GG

1.2

0.6 – 2.1

0.637

smoking exposure (packyears)

lightly exposed (11–20 PY)***

TT vs. GG

1.0

0.6 – 1.8

0.928

lightly exposed (11–20 PY)***

TG vs. GG

1.0

0.5 – 1.7

0.857

moderately exposed (21–30 PY)***

TT vs. GG

1.0

0.6 – 1.7

0.960

moderately exposed (21–30 PY)***

TG vs. GG

0.9

0.6 – 1.6

0.822

highly exposed (31++ PY)***

TT vs. GG

0.9

0.5 – 1.4

0.595

highly exposed (31++ PY)***

TG vs. GG

0.8

0.5 – 1.3

0.369

*conditional to age-strata (3 groups: ≤ 40 years, 41–45 years, 46–50 years), adjusted for smoking exposure; **conditional to age/gender-strata (6 groups) and adjusted for smoking exposure; ***conditional to age/gender-strata (6 groups)

Table 4

Association of MDM2 SNP309 with lung cancer within NSCLC cases

genotype

95% CI

p-value

all: NSCLC cases (n = 434) vs. controls (n = 1295)

TG vs. GG

1.1^§

0.7–1.6

0.828

TT vs. GG

1.0^§

0.7–1.5

0.841

men: NSCLC cases (n = 280) vs. controls (n = 815)

TG vs. GG

1.2^§§

0.7–2.9

0.422

TT vs. GG

1.2^§§

0.7–2.9

0.515

women: NSCLC cases (n = 154) vs. controls (n = 479)

TG vs. GG

0.8^§§

0.4–1.6

0.471

TT vs. GG

0.7^§§

0.4–4.0

0.323

gender difference in genotypic ORs

0.237

^§conditional to age/gender-strata (6 groups) and adjusted for smoking exposure^§§conditional to age-strata (3 groups) and adjusted for smoking exposure and gender

Table 5

MDM2 SNP309 genotypes

Group

MDM2 SNP309 genotypes

Cases (n = 635)

Controls

LUCY-study

(n = 472)

HLC-study

(n = 163)

KORA-study

(n = 1300)

gender

men

128 (41%)

47 (49%)

350 (43%)

148 (48%)

42 (44%)

366 (45%)

33 (11%)

7 (7%)

99 (12%)

unknown

1 (0%)

3 (0%)

women

71 (44%)

24 (36%)

197 (41%)

74 (46%)

29 (43%)

232 (48%)

16 (10%)

14 (21%)

50 (10%)

unknown

1 (0%)

3 (0%)

age at diagnosis

≤ 40 years

30 (44%)

11 (50%)

85 (43%)

30 (44%)

8 (36%)

91 (46%)

6 (9%)

3 (14%)

21 (11%)

unknown

2 (3%)

2 (1%)

41–45 years

58 (39%)

21 (43%)

172 (44%)

73 (49%)

23 (47%)

185 (47%)

19 (13%)

5 (10%)

37 (9%)

unknown

1 (0%)

46–50 years

111 (44%)

39 (42%)

290 (41%)

119 (47%)

40 (43%)

322 (46%)

24 (9%)

13 (14%)

91 (13%)

unknown

3 (0%)

smoking exposure level (SEL)

minimally exposed

28 (49%)

7 (33%)

297 (42%)

(0–10 PY)

19 (33%)

12 (57%)

332 (47%)

9 (16%)

2 (10%)

81 (11%)

unknown

1 (2%)

2 (0%)

lightly exposed (> 10–20 PY)

29 (36%)

7 (54%)

72 (40%)

42 (52%)

5 (38%)

81 (46%)

9 (11%)

1 (8%)

24 (13%)

unknown

1 (1%)

moderately exposed (> 20–30 PY)

65 (45%)

13 (39%)

81 (44%)

70 (49%)

15 (45%)

86 (46%)

9 (6%)

5 (15%)

19 (10%)

unknown

highly exposed

76 (41%)

41 (48%)

84 (44%)

(> 30++ PY)

89 (48%)

33 (39%)

87 (45%)

21 (11%)

11 (13%)

21 (11%)

unknown

LC subtypes

NSCLC- Adenocarcinoma

63 (41%)

35 (50%)

75 (49%)

23 (33%)

13 (9%)

12 (17%)

unknown

1 (1%)

other NSCLC

68 (43%)

17 (30%)

73 (46%)

34 (60%)

19 (12%)

6 (11%)

SCLC

55 (45%)

15 (50%)

55 (45%)

12 (40%)

13 (11%)

3 (10%)

other types

13 (27%)

4 (40%)

19 (39%)

2 (20%)

4 (8%)

unknown

13 (27%)

4 (40%)

Furthermore it was investigated whether an interaction existed between the MDM2 SNP309 and the smoking status. We did not find an association between the MDM2 SNP309 and lung cancer for any of the defined smoking exposure level groups (Table 3, 5).

Even though no significant difference between both case-populations could be stated statistically, we observed twice as many female GG-carriers among HLC-cases (21%) than in the control- or LUCY population (10%) (Table 5). We also observed an enrichment of NSCLC- and NSCLC adenocarcinoma-cases in the HLC-sample (78%) compared to the LUCY-sample (66%). Lind et al. (2006) 6 recently reported a gender specific risk disposing effect of the T-allele of MDM2 SNP309 for NSCLC cases. We therefore additionally performed a subgroup analysis restricted to NSCLC-cases and tested for gender differences. Compared to the GG genotype, the smoking adjusted ORs for the TG and TT genotypes for female NSCLC-cases were 0.8 (95% CI: 0.4–1.6) and 0.71 (95% CI: 0.4–4.0), respectively. For men the ORs were 1.2 (95% CI: 0.7–2.8) and 1.2 (95% CI: 0.7–2.9), respectively (Table 4). Although a possible NSCLC risk modification of MDM2 SNP309 seems to be reverse between men and women, we failed to achieve significance for this gender difference (p = 0.237). We also tested a gender specific genetic association within both case-samples separately. Neither within all HLC-cases (p = 0.083) nor within all LUCY-cases (p = 0.778) were significant gender differences found (Table 2).

MDM2 SNP309 was recently reported to be associated with an earlier onset of disease 4. The average age at the time of diagnosis in our cases overall was not significantly different (p = 0.923) between the variant genotypes (Table 1) and can be assumed as homogeneous between both case-samples (p = 0.7157). The mean age of diagnosis of men was 45.2 (median = 46.0 years, range 26.0 – 50.0 years) and of women 44.7 years (median = 46.0 years, range 24.0 – 50.0 years). Women, however, with the MDM2 SNP309 were diagnosed at a younger age (8 months) compared to males, but this was not statistically significant (p = 0.059, 95% CI: 0 to 16 months). Within the LUCY-case population this gender difference was 10 months (95% CI: 0.3 to 20 months, p = 0.044), and only 6 months (95% CI: -10 to 22 months, p = 0.496) in the much smaller HLC-case population.

Discussion

Reports have shown an increased risk of lung cancer for the G allele of the MDM2 SNP309 in Korean and Chinese populations 71617. In contrast, in our study of 635 Caucasian lung cancer patients with age of onset < 51 years and 1300 controls the MDM2 SNP309 was not associated with lung cancer. We did not observe a significant overall association either with the G allele or with the T allele as reported by Li et al. (2006) where they showed an increased lung cancer risk with the T/T genotype in a non-Hispanic white population 18. We had a 90% power (alpha = 0.05, two sided test) to detect a minimum overall OR of 1.4 for the MDM2 SNP309 T allele. Thus our study had sufficient power to detect an OR of 1.6 (95% CI: 1.1–2.5) and 1.8 (95% CI: 1.5–2.3) reported in other studies 67. The estimated allele frequency (T: 0.66, G: 0.34) agrees well with further reported allele frequencies in Caucasian populations 68. Differences between the two case populations were statistically not palpable (Table 1, 2, 3, 4, 5) but the HLC-sample was enriched with NSCLC-cases. According to Steffens et al. 2006 12 we can assume the German population to be nearly free of population stratification, which may lead to false positive or false negative association findings in genetic case control studies. Differences in ethnicity between our population and those reported by Zhang et al. 2006 7, Park et al. 2006 16 and Jun et al. 2007 19 may provide a partial explanation for the lack of association in our study. On the other hand Hu et al. 2006 5 also did not observe an association between the MDM2 SNP309 and lung cancer in a Chinese population. Our results were similar to the report of Pine et al. (2006) 8. They also did not find any overall association between the MDM2 SNP309 and lung cancer in a Caucasian (USA) population. Similarly, we did not observe an interaction between the MDM2 SNP309 and smoking. A combined analysis of the available genotype data of the MDM2 SNP309 showed an increased risk of lung cancer for the GG versus the TT genotype (OR: 1.3, 95% CI: 1.1–1.4) 20. A main difference between the two study populations is the age of cases. Therefore one possible explanation would be, that the MDM2 variant is only associated with risk of later onset lung cancer. On the other hand a large study of 1787 Caucasian lung cancer patients could also not confirm the results of this meta-analysis. They did not find any significant association of the MDM2 SNP309 and lung cancer 21. The populations used in the meta-analysis are mostly of Asian origin so possibly pointing to population heterogeneity.

Lind et al. (2006) 6 recently reported a gender specific risk disposing effect of the T allele of MDM2 SNP309 for NSCLC cases. They investigated NSCLC-cases and found female carriers of the GG-genotype associated to LC by an OR of 4.1, while male homozygotes showed a non significant OR of 1.3. Our data slightly tends to confirm this finding, but the corresponding OR for NSCLC women is just 1.4 (1/0.71 of Table 4), which is much smaller and not significant (p = 0.323). In our study none of the gender specific ORs nor a test of gender differences yielded significance. But we noticed discrepancies of such a gender specific genetic association between the two case-samples of our investigation. A gender difference was almost significant (p = 0.08) for the much smaller single center case-sample of the HLC-study. There, the OR for female carriers of the GG-Genotype (corresponding to Lind et al. (2006)) was 1.9 (1/0.54 of Table 4) and for male carriers 0.6 (1/1.56 of Table 4). With n = 67 female and n = 96 male cases these subsamples are quite small and the tests for association are underpowered. Thus our investigation provides no significance for such gender specific associations by itself. Comparing our study samples to that of Lind et al. (2006) the major difference is the age of onset of LC. The presented investigation focused on early onset LC cases which are in the mean 20 years younger than those of Lind et al. (2006). As the population by Lind et al. (2006) is of Norwegian origin there might also be different gene-environmental interactions.

MDM2 SNP309 was reported by Bond et al. 2004 4 to be associated with an earlier onset of disease for Li-Fraumeni syndrome and sporadic sarcoma patients. We did not observe a lower age of diagnosis in our study, similar findings are also described by Hu et al. 2006 5 and Pine et al. 2006 8. Our sample size is large enough to detect a shift of two years for the time of diagnosis with 90% power (alpha = 0.05) for heterozygous as well as for homozygous allele carriers. Recently Bond et al. 2006 22 reviewed the possible interaction between the SNP309 and the oestrogen receptor status in women. Within women of the LUCY case population we could observe an earlier onset of disease of 10 months (95% CI: 0.3 to 20 months, p = 0.044), but only 6 months (95% CI: -10 to 22 months, p = 0.496) in the by far smaller HLC-case population. Recent data suggest that the promoter polymorphism in the MDM2 gene may influence the age of cancer onset in a gender specific way 232425.

Conclusion

Given that lung cancer is a result of gene-environmental interaction, the genetic component may be a particularly strong risk factor among early onset lung cancer patients. In our sample, after controlling for gender and other characteristics, the overall data suggest that the MDM2 SNP309 might not be a sufficient risk factor of lung carcinogenesis not even in young cases where the genetic component might have a larger contribution to the risk of disease. It might modify the time of tumour onset, especially in women, supporting the model, that female-specific hormones, such as oestrogen, could allow the SNP309 to accelerate tumour formation. Our investigation provides no significance for gender specific associations by itself; it points only towards gender specific differences. Therefore further studies have to be conducted to explicitly study these gender-specific effects.

Abbreviations

CI: confidence interval; HLCS: Heidelberg lung cancer study; KORA: Cooperative Health Research in the Augsburg Region; LC: lung cancer; LUCY: lung cancer in the young; MALDI-TOF: matrix-assisted laser desorption/ionization time-of flight; NSCLC: none small cell lung cancer; OR: odds ratio; PY: packyear; SCLC: small cell lung cancer.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

KM carried out the molecular genetic study and drafted the manuscript. WS, NK carried out the molecular genetic study. AR, JCC performed the statistical analysis. HEW, HB, ARi, TI conceived the study, and participated in its design and coordination. GW proband recruitment and data acquisitions. MT data acquisitions. NK, HD, EM, GS, MC, MD, HM, PD, AG, KG, KH, GH, CS, BJ, WS, YK, DT recruited the lung cancer cases in different hospitals. All authors read and approved the final manuscript.

Acknowledgements

The computational assistance of G. Fischer, H. Grallert and C. Gieger, Institute of Epidemiology, GSF-National Research Center for Environment and Health, Neuherberg, Germany is gratefully acknowledged. We thank Rolf Holle, C. Hanrieder and A. Steinwachs, Institute of Epidemiology, GSF-National Research Center for Environment and Health, Neuherberg, Germany for their assistance in data management. We also thank all individuals who participated as cases or controls in this study and the KORA Study Center and their co-workers for organizing and conducting the data collection. The authors wish to thank all patients, their physicians and nurses involved in sample and data collection in the following hospitals: Dr. Heidi Kleen – Aurich, Lungenklinik Heckeshorn – Berlin, Berufsgenossenschaftliche Kliniken Bochum, Medizinische Poliklinik der Universität Bonn, Pneumologische Klinik des Zentralkrankenhaus Bremen Ost, Bereich Innere Medizin des Fachkrankenhaus Coswig GmbH, Fachklinik für Atemwegserkrankungen – Donaustauf, Abt. Pneumologie – Ruhrlandklinik Essen, II. Medizinische Klinik des Wald-Klinikum Gera, Pneumologische Klinik – Greifenstein, Zentrum für Pneumologie und Thoraxchirurgie des Krankenhaus Großhansdorf, Klinik für Pneumologie am Klinikum Hannover Heidehaus, Abt. Innere Medizin-Onkologie der Thoraxklinik – Heidelberg, Innere Medizin V des Universitätsklinik des Saarlandes – Homburg, Fachklinik für Lungenerkrankungen – Immenhausen, Innere Medizin des Klinikum Chemnitz – Krankenhaus Küchwald, Abt. Pneumologie der Universitätsklinik Leipzig, Robert-Koch-Klinik des Städtischen Klinikums St. Georg – Leipzig, Abt. Pneumologie des Klinikum der LMU-München, Pneumologische Klinik, München-Gauting, Lungenklinik Unterstedt des Diakoniekrankenhaus Rotenburg. We are also grateful to the LUCY-Consortium and the KORA Study Group (Head: H.E. Wichmann).

This work was funded in part by the National Genome Research Network (NGFN), the DFG (BI 576/2-1; BI 576/2–2), the Helmholzgemeinschaft (HGF) and the Federal office for Radiation Protection (Bfs: STSch4454). Genotyping was performed in the Genome Analysis Center (GAC) of the GSF Research Center for Environment and Health. The KORA Surveys were financed by the GSF, which is funded by the German Federal Ministry of Education, Science, Research and Technology and the State of Bavaria. Recruitment of the cases in Heidelberg was in part financed by the Deutsche Krebshilfe.

Mdm-2: "big brother" of p53 Momand J Zambetti GP J Cell Biochem 1997 64 343 352 10.1002/(SICI)1097-4644(19970301)64:3<343::AID-JCB1>3.0.CO;2-V 9057092 Functions of the MDM2 oncoprotein Freedman DA Wu L Levine AJ Cell Mol Life Sci 1999 55 96 107 10.1007/s000180050273 10065155 Regulation of p53 stability by Mdm2 Kubbutat MH Jones SN Vousden KH Nature 1997 387 299 303 10.1038/387299a0 9153396 A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans Bond GL Hu W Bond EE Robins H Lutzker SG Arva NC Bargonetti J Bartel F Taubert H Wuerl P Onel K Yip L Hwang SJ Strong LC Lozano G Levine AJ Cell 2004 119 591 602 10.1016/j.cell.2004.11.022 15550242 Genetic variants in the MDM2 promoter and lung cancer risk in a Chinese population Hu Z Ma H Lu D Qian J Zhou J Chen Y Xu L Wang X Wei Q Shen H Int J Cancer 2006 118 1275 1278 10.1002/ijc.21463 16152608 Association of a functional polymorphism in the promoter of the MDM2 gene with risk of nonsmall cell lung cancer Lind H Zienolddiny S Ekstrom PO Skaug V Haugen A Int J Cancer 2006 119 718 721 10.1002/ijc.21872 16496380 Genetic polymorphisms in cell cycle regulatory genes MDM2 and TP53 are associated with susceptibility to lung cancer Zhang X Miao X Guo Y Tan W Zhou Y Sun T Wang Y Lin D Hum Mutat 2006 27 110 117 10.1002/humu.20277 16287156 MDM2 SNP309 and SNP354 are not associated with lung cancer risk Pine SR Mechanic LE Bowman ED Welsh JA Chanock SC Shields PG Harris CC Cancer Epidemiol Biomarkers Prev 2006 15 1559 1561 10.1158/1055-9965.EPI-06-0217 16896050 KORA--a research platform for population based health research