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Journal of Clinical Oncology, Vol 22, No 22 (November 15), 2004: pp. 4575-4583 © 2004 American Society of Clinical Oncology. DOI: 10.1200/JCO.2004.01.091 Prognostic Factors in Resected Stage I NonSmall-Cell Lung Cancer: A Multivariate Analysis of Six Molecular MarkersFrom the Departments of Thoracic/Head and Neck Medical Oncology, Clinical Cancer Prevention, Pathology, and Biostatistics, The University of Texas M.D. Anderson Cancer Center, Houston, TX; Institut Gustave Roussy, Villejuif, France; and Winship Cancer Institute, Emory University, Atlanta, GA Address reprint requests to Charles Lu, MD, SM, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Box 432, Houston, TX 77030-4009; e-mail: clu{at}mdanderson.org
PURPOSE: To analyze the prognostic significance of six molecular biomarkers (death-associated protein kinase [DAPK] promoter methylation, interleukin-10 [IL-10] protein expression, cyclooxygenase-2 [COX-2] mRNA expression, human telomerase reverse transcriptase catalytic subunit [hTERT] mRNA expression, retinoic acid receptor-beta [RAR-ß] mRNA expression, and K-ras mutational status) in stage I nonsmall-cell lung cancer (NSCLC) patients. PATIENTS AND METHODS: Biomarker analyses were performed on tumors from 94 patients with stage I NSCLC who underwent surgical resection at our institution. A minimum follow-up period of 5 years was required. DAPK methylation was assessed by methylation-specific polymerase chain reaction (PCR). RAR-ß, COX-2, and hTERT mRNA levels were determined by in situ hybridization with digoxigenin-labeled antisense riboprobes. K-ras mutation status was determined by the PCRprimer introduced restriction with enrichment for mutant alleles method. IL-10 protein expression was analyzed by immunohistochemistry using a polyclonal antihuman IL-10 antibody. Cancer-specific survival was analyzed with a Cox proportional hazards model. To identify independent prognostic factors, a stepwise selection method was used. RESULTS: DAPK methylation, IL-10 lack of expression, COX-2 expression, hTERT expression, RAR-ß expression, and K-ras mutations were observed in 46.8%, 29.8%, 59.6%, 34.0%, 23.4%, and 34.0% of patients, respectively. In the final model, DAPK methylation and IL-10 lack of expression were significant negative prognostic factors for cancer-specific survival, whereas COX-2 expression was of borderline significance. CONCLUSION: In this cohort of resected stage I NSCLC patients, molecular markers that independently predict cancer-specific survival have been identified. The prognostic roles of DAPK methylation, IL-10, and other biomarkers in NSCLC merit further investigation.
Lung cancer remains a worldwide public health issue of immense proportions. In the year 2003, cancers of the lung and bronchus are expected to continue to account for the most cancer deaths in the United States (157,200 deaths or 28.2%), more than the estimated total number of deaths as a result of cancers of the breast, prostate, colon, and rectum combined.1 Approximately 80% of lung cancers will have nonsmall-cell carcinoma histology.2 Approximately 25% of patients present with early-stage disease.3 The standard treatment is surgical resection with appropriate lymph node sampling or dissection. Although early-stage nonsmall-cell lung cancer (NSCLC) patients have a relatively favorable prognosis, the risk of disease recurrence and death remains substantial. Five-year survival rates for pathologic stages I and II disease are 57% to 67% and 38% to 55%, respectively.4 Identification of reliable prognostic factors for disease recurrence and death could have significant clinical import. Patients in a high-risk group, for example, would be appropriate candidates for novel adjuvant or chemoprevention strategies. Both our group5-12 and others13-16 have focused on identifying molecular prognostic factors in early-stage NSCLC. We have established a retrospective cohort of stage I NSCLC patients who underwent surgical resection at our institution. Over the past few years, investigators in our group have analyzed a number of tumor biomarkers within this valuable clinical research database. Given the roles that retinoids play in the regulation of cell growth, differentiation, and apoptosis, Khuri et al8 investigated the prognostic significance of retinoic acid receptor-beta (RAR-ß) mRNA expression in 156 patients. Because RAR-ß expression seems to be suppressed during carcinogenesis, these investigators hypothesized that lower RAR-ß levels would predict a poor clinical outcome. Surprisingly, overall survival was significantly worse in patients with strongly positive RAR-ß expression. Because one RAR-ß isoform, RAR-ß4, may promote hyperplasia and neoplasia,17 the authors hypothesized that differential expression of RAR-ß isoforms may be a possible explanation for their unexpected findings. Khuri et al9 subsequently evaluated cyclooxygenase-2 (COX-2) mRNA expression and correlated it with the expression of RAR-ß in this cohort of stage I NSCLC patients. COX-2 overexpression had previously been demonstrated in lung, head and neck, and other tumors,18-20 and cell line data indicated that retinoic acid could suppress COX-2.21 These investigators found that COX-2 expression was associated with worse overall and disease-free survival and that COX-2 and RAR-ß mRNA levels were correlated. These findings were in conflict with the prior cell line data, which would have predicted that RAR-ß upregulation should downregulate COX-2. Telomerase is a ribonucleoprotein that lengthens and maintains the ends of chromosomes that are shortened with successive cell divisions.22 Telomerase is expressed in up to 85% of NSCLC tumors and plays a critical role in sustaining cellular immortality and carcinogenesis.23,24 Wang et al11 examined mRNA expression of the human telomerase reverse transcriptase catalytic subunit (hTERT) in 153 patients from our database. Positive hTERT expression was significantly associated with worse overall and disease-specific survival. Tang et al7 examined hypermethylation of the death-associated protein kinase (DAPK) promoter in 135 patients from this cohort. Epigenetic inactivation of tumor suppressor genes by promoter hypermethylation frequently occurs in NSCLC.25,26 DAPK is a putative tumor-suppressor gene that encodes for a calmodulin-dependent kinase that possesses a death domain at its C terminus.27 DAPK is required for interferon-gammainduced apoptosis and seems to suppress the metastatic ability of lung cancer cells.28 In the study by Tang et al,7 DAPK hypermethylation was significantly associated with poorer overall and disease-specific survival. Soria et al12 examined the role of interleukin-10 (IL-10) protein expression among 135 patients. The immunomodulatory effects of IL-10 have demonstrated conflicting results in various tumor systems. Some reports support the role of IL-10 in helping tumors evade immunosurveillance because IL-10 can inhibit macrophage, T-cell, and antigen-presenting cell functions.29,30 Others have demonstrated that IL-10 may function as a potent inhibitor of tumor growth and metastasis.31,32 In this study, IL-10 lack of expression was significantly associated with poorer overall and disease-specific survival. The aforementioned hypothesis-driven studies each focused on one or a few biomarkers. To simultaneously examine multiple potential molecular prognostic factors in this clinical research database, we identified 94 patients who had complete information for a panel of six biomarkers (RAR-ß, COX-2, hTERT, DAPK promoter methylation, IL-10, and K-ras). Multivariate Cox regression analysis was used to identify independent predictors of cancer-specific survival in this population of resected stage I NSCLC patients.
Study Population Five hundred ninety-five consecutive patients with stage I NSCLC underwent definitive surgical resection, defined as a lobectomy or a pneumonectomy, from 1975 to 1990 at The University of Texas M.D. Anderson Cancer Center (Houston, TX). Patients did not receive preoperative or postoperative chemotherapy or radiotherapy. We retrospectively identified 185 patients for whom both tissue samples and a median follow-up period of more than 5 years were available. All available tissue blocks were reviewed by a thoracic pathologist (B.K.), and 163 cases had adequate tumor present in the surgical specimen. The patient population was identified through a search of the Tumor Registry database maintained by the Department of Medical Informatics at The University of M.D. Anderson Cancer Center. Survival status was verified and updated from Tumor Registry records as of December 1, 2000. This study was reviewed and approved by the institutional review board and conducted in accordance with its policies. Five published studies7-9,11,12 had previously examined different molecular prognostic factors among the 163 patients with sufficient tumor specimens and more than 5 years of follow-up data. The sample sizes ranged from 135 to 160 patients. A total of 94 patients had complete information for a panel of six biomarkers, and these patients were included in our analysis.
Methylation-Specific Polymerase Chain Reaction (PCR)
Immunohistochemical Staining for IL-10 Protein The IL-10 labeling index was defined as the percentage of tumor cells displaying cytoplasmic immunoreactivity and was calculated by counting IL-10stained tumor cells among at least 1,000 tumor cells for each section as previously described.12 On the basis of previous reports, if 10% or more of the tumor cells were positive for IL-10, the case was considered to be IL-10 positive.35 All slides were scored concomitantly by a pathologist (X.T.) and another investigator (J.-C.S.) in a blinded manner.
hTERT In Situ Hybridization (ISH)
COX-2 and RAR-ß ISH
K-ras Mutation Analysis With PCRPrimer Introduced Restriction With Enrichment for Mutation Alleles (PCR-PIREMA) Briefly, PCR around K-ras codon 12 was performed using a mismatched primer (forward primer: 5'-TGAATATAAACTTGTGGTAGTTGGACCT-3'; reverse primer: 5'-CTGTATCAAAGAATGGTCC TGCACC-3') that introduced an MvaI restriction site into the PCR products derived from normal alleles. MvaI digestion of the PCR products left only the PCR products derived from mutant alleles intact, after which further PCR selectively amplified the mutant PCR products. The first PCR reaction was performed with mixtures containing 0.5 µL of DNA recovery solution, 10 ng of each nucleotide, and the mismatched primer to introduce an Mva I restriction site flanking the K-ras exon 1, with 15 cycles at an annealing temperature of 55°C. The first PCR products were digested with MvaI and diluted 1:100. One microliter of the diluted product was amplified by 20 cycles of PCR with the same primers at an annealing temperature of 40°C, and the products were digested with MvaI a second time. The second PCR products were diluted 1:100, amplified by 35 cycles with the previous forward primer and a new reverse primer (5'-CTCTATTGTTGGATCATATTCGTCCAC-3') at an annealing temperature of 65°C, and digested with MvaI a third time. The final digested products were then electrophoresed on 2.5% agarose gels and stained with ethidium bromide. A digestion-resistant 106-bp band indicated the presence of a K-ras codon 12 mutation. Extensive measures were taken to prevent cross-contamination of samples. A normal control sample and a known mutation sample were included in all of the experiments.
Statistical Analyses All survival curves were calculated from the date of surgery. Overall survival took all deaths (cancer related or not) into account. Disease-specific survival time was calculated from the date of surgery to death from cancer-related causes. Disease-free survival time was calculated from the date of surgery to relapse or death from cancer-related causes.
Data for a panel of six molecular markers (RAR-ß, COX-2, hTERT, DAPK promoter methylation, IL-10, and K-ras) were available for 94 patients in our retrospective cohort. These patients were the study population for our analysis. Patient characteristics are listed in Table 1. Median follow-up time for alive patients and those lost to follow-up was 10.9 years. Sixty-nine patients have died. Twenty-nine deaths were cancer related.
The frequency of each molecular marker, displayed as a negative prognostic factor, is listed in Table 2. Univariate analyses of each molecular marker and its association with disease-specific survival and overall survival were performed (Table 3). Similar univariate survival analyses of clinical variables (age, sex, and smoking status) were performed. A highly significant association was demonstrated between age (< 60 years v 60 years) and overall survival (P = .003). Sex and smoking status were not associated with overall or disease-specific survival. Age 60 years was associated with a significant increased risk of noncancer-related death (P < .001) and was not associated with disease-specific survival (P = .577). This phenomenon is likely explained by the relatively long follow-up of these subjects and by the fact that that the majority of deaths (40 of 69 deaths) were unrelated to cancer. In light of these findings, we reasoned that disease-specific survival would serve as a more clinically relevant end point for this cohort, although we continued to include overall survival in our analyses. Disease-specific survival stratified by each molecular marker is shown in Figure 1.
A multivariate Cox proportional hazards model was created to identify predictors of disease-specific survival (Table 4). DAPK promoter methylation and IL-10 lack of expression were significant negative prognostic factors for disease-specific survival, whereas COX-2 expression was of borderline significance. The same variables were selected when tumor stage, histology, smoking status, and sex were included in the model. The poorer disease-specific and overall survival of patients with both DAPK methylation and IL-10 lack of expression are illustrated in Figure 2. We defined these patients as a high-risk group, and the remaining patients were defined as a low-risk group. A log-rank test assessing the difference in survival between these groups was statistically significant for both disease-specific survival (P < .0001) and overall survival (P < .0001). We note that the definitions of the high- and low-risk groups are data dependent. That is, the definition of high risk was not determined a priori. A similar model for overall survival yielded three significant negative prognostic factors (age 60 years, P = .0017; COX-2 expression, P = .021; and DAPK methylation, P = .044), whereas IL-10 lack of expression was of borderline significance (P = .069).
Exploratory analyses of the relationships between the various molecular markers were performed. Significant associations were found between hTERT and COX-2 expression (odds ratio [OR], 6.14; 95% CI, 2.09 to 18.04; P = .0004) and K-ras mutations and DAPK methylation (OR, 2.64; 95% CI, 1.10 to 6.36; P = .032). Associations between IL-10 lack of expression and hTERT expression (OR, 2.63; 95% CI, 1.06 to 6.67; P = .056), IL-10 lack of expression and COX-2 expression (OR, 2.63; 95% CI, 0.99 to 7.14; P = .066), and COX-2 expression and RAR-ß expression (OR, 2.88; 95% CI, 0.96 to 8.64; P = .08) were of borderline significance. We also investigated other models by performing all two-variable, three-variable, and four-variable multivariate models. On the basis of these analyses, only DAPK methylation and IL-10 lack of expression were statistically significant (P < .05) for all models. Furthermore, the three-variable model, including DAPK methylation, IL-10 lack of expression, and COX-2 expression, had the lowest Akaike Information Criterion (AIC) value of 224.029 (although the two-variable model that excluded COX-2 expression had an AIC of similar value). We noted that there was some evidence of association between IL-10 lack of expression and hTERT expression (OR, 2.63; P = .056) and IL-10 lack of expression and COX-2 expression (OR, 2.63; P = .066). Moreover, hTERT and COX-2 expression were highly associated (OR, 6.14; P = .0004). We ensured that the effect of these variables was not masked by colinearity by modeling them separately. Specifically, we modeled COX-2 expression with DAPK methylation (AIC = 228.135) and hTERT expression with DAPK methylation (AIC = 228.654). Neither of these models provided better fit than the model chosen.
Our findings further characterize and extend our group's previous research efforts to identify novel molecular prognostic factors in patients with early-stage NSCLC. We identified 94 patients with complete information for a panel of six molecular markers. Each biomarker had been previously studied as a prognostic factor based on its role in carcinogenesis. When analyzed individually, five of these biomarkers (RAR-ß, COX-2, hTERT, DAPK promoter methylation, and IL-10) were demonstrated in prior studies7-9,11,12 by our group to be significant predictors of survival. One available marker (K-ras) was included in the current analysis based on published data demonstrating that it had prognostic significance in early-stage NSCLC,14,42 even though it did not have prognostic significance in univariate analysis in our patients. Our multivariable analysis indicates that two biomarkers (DAPK promoter methylation and IL-10) function as independent predictors of disease-specific survival, and a third biomarker (COX-2) is of borderline significance in this cohort. These findings should be confirmed in other NSCLC patient populations. Our results further support the importance of epigenetic gene regulation in lung carcinogenesis. Others have demonstrated that aberrant promoter methylation of DAPK and other genes frequently occurs in NSCLC tumors,25,26 suggesting that methylation may be a common mechanism of inactivation of cancer-related genes. DAPK promoter methylation was the most statistically significant predictor of survival in our study. Kim et al43 investigated the role of DAPK methylation in 185 NSCLC patients who underwent surgical resection, including 102 patients with stage I disease. DAPK methylation was significantly correlated with advanced stage, suggesting that DAPK may be important in the progression of NSCLC. Stage I patients with DAPK methylation had worse overall survival, although this association was not statistically significant. The authors noted that patient follow-up data was limited, and this factor may have contributed to their findings. Harden et al44 examined promoter methylation of a panel of five genes in tumors and lymph nodes of 90 stage I NSCLC patients. Interestingly, patients with both DAPK and adenomatous polyposis coli gene methylation had poorer overall survival that did not reach statistical significance, although the methylation of either gene alone was not a predictor of survival. Possible explanations for these results include the relatively low frequency of DAPK methylation (17%) compared with our findings (47%). The smaller number of patients with DAPK methylation (n = 15) would result in the study having less power to detect significant associations with survival.
The role of IL-10 in carcinogenesis remains controversial. Our findings indicate that loss of IL-10 expression predicts poor disease-specific survival in early-stage NSCLC. Human bronchial epithelial cells constitutively produce IL-10, which may regulate the local immune response in normal lungs.34 IL-10 also seems to have significant inhibitory effects on tumor growth and metastasis in multiple animal models and tumor types, including melanoma, breast cancer, prostate cancer, and Burkitt's lymphoma.31,32,45-47 Evidence suggests that IL-10 exerts its antitumor and antimetastatic activity by inhibiting angiogenesis, and this activity is, in part, mediated by the downregulation of angiogenic molecules, such as vascular endothelial growth factor, IL-1ß, tumor necrosis factor- The data supporting the antitumor and antimetastatic activity of IL-10 are compelling, but most preclinical models using IL-10 to mediate such effects do so at concentrations that far exceed the levels demonstrated in lung cancer patients. Other authors have demonstrated that IL-10 is a potent immunosuppressive molecule that may promote lung cancer growth by suppressing T-cell and macrophage function and enabling tumors to escape immune detection.50-52 Elevated baseline serum IL-10 levels were found to be independent predictors of poorer survival in 60 advanced-stage NSCLC patients receiving platinum-based chemotherapy.53 Hatanaka et al54 measured IL-10 mRNA levels by reverse transcriptase PCR in the tumors of 82 NSCLC patients who underwent surgical resection. Their assay demonstrated IL-10 expression in 83% of the surgical specimens. In contrast to our results, IL-10 expression was significantly associated with worse survival. The reasons for these discrepant findings remain unclear. These investigators included patients with stages I to IIIb disease in their study and used a different IL-10 assay (mRNA v protein) than the assay we used in our study. These factors may have contributed to these divergent results. Our exploratory analyses demonstrate a highly significant association between hTERT expression and COX-2 expression (P = .0004). A precise explanation for this correlation is lacking, although various COX-2 inhibitors have been reported to inhibit both tumor growth and telomerase activity in mice.55,56 We also observed a significant association between K-ras mutations and DAPK methylation (P = .032). Reports suggesting that DNA methylation may be regulated by the ras signaling pathway57,58 are consistent with these findings. However, others have not found correlations between ras mutations and promoter hypermethylation in NSCLC tumors.43,59 Clearly, a better understanding of the significance of these associations will require future studies. Our analyses also demonstrate a borderline significant association between IL-10 lack of expression and COX-2 expression (P = .066).60,61 This finding is consistent with data suggesting that IL-10 has the capacity to potently downregulate COX-2. Therefore, in the absence of IL-10, COX-2 and its derived products would be more abundant and could further promote tumor progression. This study is limited by its retrospective nature and the inclusion only of patients with complete information for all six biomarkers. It is difficult to speculate on potential biases affecting our results. It is possible, for example, that small tumors with limited tissue availability were underrepresented in this cohort. These results should be validated in a separate population of NSCLC patients. In conclusion, our analysis of six molecular markers in patients with resected stage I NSCLC yielded two independent predictors of poorer disease-specific survival: DAPK methylation and IL-10 lack of expression. Future studies are warranted to further define their roles in tumor proliferation and metastasis. However, these and other potential molecular prognostic factors have yet to be validated, and thus, the integration of molecular marker assessments into the routine clinical management of NSCLC has remained an elusive goal. As the number of potential molecular markers increases, it has become more difficult to assess which prognostic factors are likely to be clinically relevant. A comprehensive multivariable analysis is not feasible because the majority of studies analyze only a single or a few biomarkers at a time. In this regard, the development of high-throughput technologies to determine gene-expression profiles and proteomic patterns of tissue specimens represents a significant methodologic advance. Several recent reports have demonstrated that mRNA and protein patterns of NSCLC tumors may be predictive of survival.62,63 Hopefully, these technologies will eventually provide the clinician with a reliable, validated molecular staging system that will improve therapeutic strategies for NSCLC.
The authors indicated no potential conflicts of interest.
Supported in part by National Cancer Institute grant No. K12 CA088084 and the Department of Defense, Biology, Education, Screening, Chemoprevention, and Treatment of Lung Cancer grant No. DAMD17-01-1-0689 and Translational Approaches for the Reversal, Genetic, Evaluation and Treatment of Lung Cancer grant No. DAMD17-02-1-0706. Presented in part at the 93rd Annual Meeting of the American Association for Cancer Research, San Francisco, CA, April 610, 2002. Authors' disclosures of potential conflicts of interest are found at the end of this article.
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Copyright © 2004 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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