
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Division of Epidemiology, University of Minnesota, Minneapolis, Minnesota 55454 [C. S.]; Center for Research on Environmental and Occupational Toxicology, Oregon Health and Science University, Portland, Oregon [V. N-S.]; Departments of Environmental Health [P. L. S., D. L. E.] and Epidemiology [T. L. V.], University of Washington, Seattle, Washington; and Program in Epidemiology, Fred Hutchinson Cancer Research Center, Seattle, Washington [T. L. V.]
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Three studies have reported on survival of lung cancer patients in relation to common polymorphisms affecting GST activity, with inconsistent results. Goto et al. (17) observed a hospital-based series of 232 NSCLC patients for ≤5 years and reported that patients who were homozygous for deletion of the GSTM1 gene (GSTM1-null genotype) had shorter survival than patients with one or two GSTM1 alleles (GSTM1 present genotype, which represents normal GSTM1 activity). In contrast, no association between mean disease-free survival time and GSTM1 genotype was reported in a series of 105 surgically treated NSCLC patients observed for 5 years (18) . In a third study of 250 lung cancer cases (all histologies were included), GSTM1 genotype, the GSTT1 gene deletion, and the GSTP1 Ile105Val single nucleotide polymorphism were studied in relation to survival, and the overall proportion surviving at 1 year was similar across categories of each GST genotype (19) . These investigations differed in several aspects of study design, including size of the study populations, observation of NSCLC patients only or of all lung cancers, length of follow-up, and choice of different end points, death versus disease-free interval. The discordant results may be related to these differences in approach.
Thus, there are plausible mechanisms through which a cancer patients inherited genotype for GST enzymes may influence his or her survival, but evidence for a role of these genetic differences in lung cancer survival is limited. Characterization of associations between drug metabolizing enzyme polymorphisms and patient prognosis could contribute to identifying individual differences in potential to benefit from particular types of therapy. We have investigated survival in relation to genotype for three common GST polymorphisms in a population-based cohort of men with lung cancer.
| Subjects and Methods |
|---|
|
|
|---|
The age range among the participants was 2874 years, with a median of 62 years. The majority (263) of the men (96%) were Caucasian, 4 were Native-American, 2 were Asian, 1 was African-American, and race was unknown for 4 men. We obtained information on stage at diagnosis (categorized according to SEER program criteria as local, regional, or distant), tumor site, histology, and type of primary therapy from the CSS. Patients with distant stage of disease at diagnosis were less likely to participate in the blood draw and, therefore, were underrepresented in the group with blood samples (31%) compared with the overall group of eligible lung cancer patients (58%). Participants with blood samples available also differed from eligible patients with no sample with regard to several other characteristics that were correlated with less advanced disease at diagnosis and/or good prognosis, so that lung cancer patients with a blood sample were less likely to be current smokers, were more likely to have a body mass index (calculated as weight in kilograms divided by height in meters, squared) above the median, were more likely to have a tumor location in the upper lobe, and were more likely to have been treated by surgery, compared with all eligible patients.
GST genotypes were determined from DNA extracted from lymphocytes. The presence of GSTM1 and GSTT1 genes was assayed by multiplex PCR (22) , and genotype at the GSTP1 Ile105Val substitution was determined by PCR and the oligonucleotide ligation assay method (23) , with primers and probes for GSTP1 as described previously (24) .
Subjects were followed for vital status through 2000 by the CSS by active follow-up and matching to electronic death certificate records from the state of Washington and the National Center for Health Statistics. Survival analysis methods were used to consider the influence of GST genotypes on patient survival. We calculated survival time as the time from diagnosis to death or to the end of follow-up for each patient. Death from any cause was treated as a failure in the survival analysis, and living subjects were censored at the time of last contact. We calculated person-years at risk within each genotype category as the sum of survival times of all subjects in that category. Overall survival in relation to GST genotype was evaluated by Kaplan-Meier survival function and log-rank tests, stratified by stage at diagnosis. RR of death was estimated by the hazard ratio from a multivariate Cox proportional hazards model, with adjustment for categories of stage at diagnosis as strata in the model and other prognostic characteristics as covariates. RRs within subgroups according to type of therapy, and by tumor histology, were calculated by including a multiplicative interaction term in the Cox model. The likelihood ratio test comparing models with and without the interaction term was used to evaluate the statistical significance of effect modification. Stata software (Stata Corp., College Station, TX) was used for statistical analysis.
| Results |
|---|
|
|
|---|
|
2 = 3.36, 1 df, P = 0.07), there was an indication that GSTM1 null individuals had poor survival compared with GSTM1 present subjects. The Kaplan-Meier estimates of overall survival at 1, 3, and 5 years were 0.77 (95% CI 0.690.84), 0.39 (96% CI 0.300.47), and 0.29 (95% CI 0.220.37) for GSTM1 present subjects and 0.77 (95% CI 0.690.83), 0.34 (95% CI 0.260.41), and 0.2 (95% CI 0.140.27) for GSTM1 null subjects. There was no evidence of a survival difference by GSTT1 genotype (
2 = 0.77, 1 df, P = 0.38), nor by GSTP1 genotype (
2 = 0.12, 2 df, P = 0.94).
|
|
|
|
| Discussion |
|---|
|
|
|---|
The study population that we followed for survival was a population-based sample, and, through the CSS registry, we were able to observe almost all of the participating lung cancer patients from time of diagnosis to ≥5 years or until death. The number of deaths observed during the follow-up period (214) was large enough to provide reasonable power to assess the main effects of the genotypes of interest and rule out any strong associations of GSTT1 or GSTP1 with survival. The GSTM1-survival association was significant; however, the lower 95% confidence limit approached 1. Because the study population was limited to men, and the source population was largely Caucasian, results may not be generalizable to female lung cancer patients or members of other ethnic or racial groups.
The cohort of patients for whom we obtained blood for genotyping represented 42% of the overall eligible population, and participants tended to have lower stage at diagnosis and somewhat better survival than nonparticipants. Poor participation can introduce selection bias in a cohort study when two conditions are met: (a) participation is related to survival; and (b) participation differs according to exposure status, independent of the exposures influence on survival. In the present study, participation was related to survival, so one condition that contributes to bias is present. GST genotypes of nonparticipants are not known, so we are unable to evaluate whether these exposures were related to participation. However, GST genotypic variants do not produce any evident phenotype that would be expected to affect an individuals tendency to participate in a study, so it is unlikely that the second condition was met. Because survival analysis methods rely on comparisons within the cohort of participating patients, differences between participants and nonparticipants should not introduce bias into our estimates of RRs, although generalizability to those who do not survive long after diagnosis may be limited.
Considered in context of previous studies, our result regarding GSTM1 and lung cancer survival is consistent with the GSTM1-survival association described in a study which was similar in design, having a large study population and several years of follow-up. Goto et al. (17) reported that, among 232 NSCLC patients, those with the GSTM1 null genotype had worse survival, with 44% of GSTM1 null patients surviving at 3 years, compared with 55% of patients with GSTM1 present. These results are quite comparable with our study population, in which, when NSCLC cases only were considered, 42% of GSTM1 null versus 48% of GSTM1 present patients survived to 3 years. Yang et al. (19) reported no overall differences in lung cancer survival at 1 year according to GSTM1 genotype. We note that in the present study data, survival at 1 year was essentially identical (77%) in the two GSTM1 genotype categories. It was at 3 and 5 years of follow-up that the increased risk of death among GSTM1-null patients became apparent. Thus, the data presented by Yang et al., after only 1 year of follow-up, are not inconsistent with those of the present study. The third published study of GSTM1 and lung cancer survival that may be compared with the current investigation is the study conducted by Przygodzki et al. (18) . This study found no association between GSTM1 and survival, but because of its smaller study population (n = 105), it would not have had statistical power to detect an association of the magnitude that was observed in our data.
Because GST enzymes are of interest as potential modifiers of the effects of chemotherapy and radiation therapy, we analyzed the associations between all three GST polymorphisms and survival by type of therapy. We found that the GSTM1-survival association was not modified by chemotherapy but appeared to be strongest among patients treated by radiation. The biological significance of this difference according to treatment is unclear. Some limitations of the subgroup analysis by treatment should be acknowledged. Our only source of treatment information was cancer registry data, which may not be completely reliable regarding therapies. Multiple subgroup comparisons according to type of therapy were made, so chance should be considered as an explanation for the interaction between GSTM1 genotype and radiation therapy.
Although the GSTP1 allelic variants have been reported to have different activities in glutathione conjugation of both nitrogen mustard and cisplatin chemotherapy agents in vitro (7
, 8
, 25) , we did not find evidence that GSTP1 genotype influences survival among lung cancer patients, either in the overall study population or a subgroup treated with chemotherapy. GSTT1 genotype was also unrelated to survival. For both GSTP1 and GSTT1, the analysis of subgroups by type of therapy (Tables 3
and 4)
resulted in some RRs that departed from 1, but these were generally based on small numbers of deaths and not statistically significant. The GSTT1 null or GSTP1 Val/Val genotypes are each present in only
20% of individuals in the population, so given the size of our study population, we cannot rule out modest associations between GSTT1 and GSTP1 genotypes and survival. The study by Yang et al. (19)
presents the only previous data that we are aware of regarding GSTT1 and GSTP1 genotypes in relation to lung cancer survival, and its results also indicated no overall association.
Two possible mechanisms for an association between GSTM1 genotype and survival have been suggested, one involving differences in detoxification of treatment agents or GST-mediated protection against oxidative damage during treatment and the other related to differences in carcinogen damage to DNA. Under the first mechanism, individuals with GSTM1 null genotypes would experience a higher effective dose of chemotherapy and/or more reactive oxidant damage to tumor tissue. Therapy might then be more effective in GSTM1 null patients, in which case we would observe longer survival for this group, as has been reported for GSTM1 null breast cancer patients (26 , 27) . In the present study of lung cancer, the direction of the association was the reverse. Shorter survival for patients with reduced capacity for GST-mediated detoxification might be explained by more severe therapy-related toxicity. An increased number of deaths attributed to therapy-related toxicity was reported among GSTT1 null leukemia patients treated with high-dose therapy (28) . The survival difference that we observed among lung cancer patients was evident ≥3 years after diagnosis and so seems unlikely to be explained by therapy-related toxicity. A possible explanation for the association observed in our data is that GSTM1 null patients may have had dose reductions or delays caused by toxicity and, therefore, received less effective treatment. We have no information on toxicity, dose delays, or reductions in our study population. The shorter survival in association with GSTM1 null genotype that we observed is also in keeping with the model proposed by Goto et al. (17) , in which smokers with GSTM1 null genotype would have more tendency to form carcinogen-DNA adducts in lung tissue and develop cancers that contain mutations of p53, K-ras, and/or genes involved in tumor development, growth, and metastasis. Because of the presence of these mutations, the GSTM1 null patients would be expected to have more aggressive tumor biology and poorer survival, even after taking into account stage, as was observed in the present study.
If GSTM1 genotype affects lung cancer survival, as has now been described in two large study populations, this raises the possibility that survival bias may influence case control studies of GSTM1 genotype in lung cancer etiology. Shorter survival for GSTM1 null patients could result in lower prevalence of the null genotype in the group of cases who are alive and able to participate in a study. If this occurred, the observed odds ratio would be biased low. However, we observed that the proportions of GSTM1 present and GSTM1 null lung cancer patients surviving to 1 year after diagnosis were essentially identical and that survival differences only became apparent after longer follow-up. Therefore, lung cancer case control studies that have ascertained incident cases within a year after diagnosis should not be affected by survival bias. On the basis of our survival data, bias in a study addressing GSTM1 genotype in lung cancer risk would be a concern only if the case group included substantial numbers of prevalent cases.
The evidence of an association between GSTM1 null genotype and increased risk of lung cancer (2, 3, 4) , association of the same genotype with somatic changes in lung tumor tissue (12, 13, 14, 15) , as have been characterized previously, and association between GSTM1 genotype and survival, as described here, presents a complex picture. The implications for patient care, if any, are not clear. The underlying mechanism for the GSTM1-survival association should be further investigated. If the mechanism for the GSTM1-survival association is through the presence of p53 and/or K-ras mutations, as seems plausible, then our results may serve to reinforce the importance of considering GSTM1 genotype in future studies of lung cancer survival.
| Acknowledgments |
|---|
| Footnotes |
|---|
1 Supported by NIH Grants National Cancer Institute (NCI) CA53392, NCI CA62082, and National Institute of Environmental Health Sciences Center Grant ES07033. The Cancer Surveillance System (CSS) is supported by NIH contract N01-PC-67009. ![]()
2 To whom requests for reprints should be addressed, at Division of Epidemiology, University of Minnesota, 1300 South Second Street #300, Minneapolis, MN 55454. Phone: (612) 626-9096; Fax: (612) 624-0315; E-mail: sweeney{at}epi.umn.edu ![]()
3 The abbreviations used are: GST, glutathione S-transferase; CSS, Cancer Surveillance System; SEER, Surveillance, Epidemiology, and End Results; df, degrees of freedom; NSCLC, non-small cell lung cancer; RR, relative risk; CI, confidence interval. ![]()
4 Nazar-Stewart et al., submitted for publication. ![]()
Received 8/14/02; revised 3/ 4/03; accepted 3/17/03.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
M. L. Cote, W. Chen, D. W. Smith, S. Benhamou, C. Bouchardy, D. Butkiewicz, K. M. Fong, M. Gene, A. Hirvonen, C. Kiyohara, et al. Meta- and Pooled Analysis of GSTP1 Polymorphism and Lung Cancer: A HuGE-GSEC Review Am. J. Epidemiol., April 1, 2009; 169(7): 802 - 814. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y.-S. Lin, S.-C. Hung, Y.-H. Wei, and D.-C. Tarng GST M1 Polymorphism Associates with DNA Oxidative Damage and Mortality among Hemodialysis Patients J. Am. Soc. Nephrol., February 1, 2009; 20(2): 405 - 415. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Barahmani, S. Carpentieri, X.-N. Li, T. Wang, Y. Cao, L. Howe, L. Kilburn, M. Chintagumpala, C. Lau, and M. F. Okcu Glutathione S-transferase M1 and T1 polymorphisms may predict adverse effects after therapy in children with medulloblastoma Neuro-oncol, January 1, 2009; 11(3): 292 - 300. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. G. Schwartz, G. M. Prysak, C. H. Bock, and M. L. Cote The molecular epidemiology of lung cancer Carcinogenesis, March 1, 2007; 28(3): 507 - 518. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Oldenburg, S. M. Kraggerud, M. Cvancarova, R. A. Lothe, and S. D. Fossa Cisplatin-Induced Long-Term Hearing Impairment Is Associated With Specific Glutathione S-Transferase Genotypes in Testicular Cancer Survivors J. Clin. Oncol., February 20, 2007; 25(6): 708 - 714. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Yang, J. O. Ebbert, Z. Sun, and R. M. Weinshilboum Role of the Glutathione Metabolic Pathway in Lung Cancer Treatment and Prognosis: A Review J. Clin. Oncol., April 10, 2006; 24(11): 1761 - 1769. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Sugimura and P. Yang Long-term Survivorship in Lung Cancer: A Review. Chest, April 1, 2006; 129(4): 1088 - 1097. [Abstract] [Full Text] [PDF] |
||||
![]() |
J.-M. Lee, M.-T. Wu, Y.-C. Lee, S.-Y. Yang, J.-S. Chen, H.-H. Hsu, P.-M. Huang, S.-W. Kuo, C.-J. Lee, and C.-J. Chen Association of GSTP1 Polymorphism and Survival for Esophageal Cancer Clin. Cancer Res., July 1, 2005; 11(13): 4749 - 4753. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. R. Spitz, X. Wu, and G. Mills Integrative Epidemiology: From Risk Assessment to Outcome Prediction J. Clin. Oncol., January 10, 2005; 23(2): 267 - 275. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |