Ann Thorac Surg 2000;70:1861-1864
© 2000 The Society of Thoracic Surgeons
Original article: general thoracic
Neopterin: a prognostic variable in operations for lung cancer
Rupert Prommegger, MDa,
Bernhard Widner, PhDb,
Christian Murr, MDb,
Andreas Unger, MDa,
Dietmar Fuchs, PhDb,
Georg M. Salzer, MDa
a Department of Thoracic Surgery, University of Innsbruck, Innsbruck, Austria
b Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Innsbruck, Austria
Accepted for publication April 27, 2000.
Address reprint requests to Dr Prommegger, Department of Thoracic Surgery, University of Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria
e-mail: rupert.prommegger{at}uibk.ac.at
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Abstract
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Background. We studied the prognostic value of preoperatively measured neopterin to predict survival of lung cancer patients. Neopterin is produced and secreted by interferon-
-stimulated monocytic cells. High urinary neopterin concentrations are found in patients with viral infections, allograft rejection episodes, and some malignant diseases. In various tumor types high urinary neopterin concentrations are associated with a worse prognosis.
Methods. Preoperative neopterin levels of 110 patients (29 women, 81 men) with lung cancer including 7 patients with small cell lung cancer were measured and related to the time of survival after operation. Patients with clinically suspected stage IIIB lung cancer were not operated and therefore not enrolled in this study. Infectious diseases were not apparent at the time of preoperative urine sampling. Median postoperative follow-up period was 17.4 months.
Results. In a univariate analysis, patients with a preoperative neopterin concentration of more than 212 µmol/mol creatinine (4th quartile) were determined to have a significantly lower survival probability. In a multivariate analysis, a neopterin concentration of more than 212 µmol/mol creatinine (p < 0.01) and T-stage status (p < 0.005) were determined to be significantly predictive variables for worse survival prognosis.
Conclusions. Preoperative neopterin proved to be a reliable prognostic factor for survival. Immunology may provide an accurate assessment of tumor aggression and its clinical behavior. In this sense, neopterin can serve as an immunologically based estimation of malignant outgrowth. In patients who are operable by clinical tumor stage but have a high risk for operation, elevated preoperative neopterin may help in the decision for a nonoperative treatment.
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Introduction
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Neopterin (6-D-erythro-1'2'3'-trihydroxypropyl-pterin), which is synthesized from guanosine triphosphate (GTP), is released into serum and consequently excreted in urine after stimulation of monocytes/macrophages by -interferon (IFN-) [1]. The key enzyme of pteridine synthesis, GTP cyclohydrolase I, is found in neural and hepatic tissues in a constitutive form, but a cytokine-inducible form exists in many other tissues [2]. In human monocytes/macrophages, IFN- stimulates neopterin synthesis [3], whereas tumor necrosis factor alpha or lipopolysaccharides are costimulatory mediators. In viral infections, including HIV [4, 5], and in autoimmune diseases [6], elevated neopterin levels in serum and urine can be measured. In allograft recipients, elevated neopterin concentrations correlated with rejection episodes, and furthermore, neopterin was found to be a reliable predictive marker of long-term survival in these patients [7]. In various solid tumors like ovarian, cervical, prostate, colon, and hepatocellular cancer [8–12] elevated neopterin concentrations were detected in some cases and were then significantly associated with a worse prognosis. Moreover, neopterin seems to be an independent prognostic factor for early cancer death: In their study of 72 patients with lung cancer, Kronberger and coworkers [13] showed that elevated pretherapeutic urinary neopterin was significantly associated with higher rates of cancer death. However, in this study, all stages of lung cancer were included and only 33 patients were treated by surgical procedure alone. The aim of our study was to demonstrate the potential value of neopterin in decision making in operations for lung cancer.
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Patients and methods
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Patients
One hundred ten patients, 29 women and 81 men operated on with lung cancer, were enrolled in this prospective study. All clinical investigations were done before therapy was indicated. All patients were treated initially by operation alone. Preoperative staging was based mainly on computed tomography (CT) of the lung, abdomen, and brain. Additionally node biopsy by mediastinoscopy, bronchoscopy, and transthoracal biopsy was done if appropriate. Median age at diagnosis was 64 years (range, 24 to 85 years). T-stage levels were T1 (n = 36), T2 (n = 53), T3 (n = 17), T4 (n = 3). Grading was classified by I to III and nodal stage by N0 to N2. Patients with clinical stage IIIB were not operated on and therefore not included in this study. There were 7 small lung cancers and 103 nonsmall cell lung cancers (47 squamous cell cancers, 29 adenocarcinomas, 13 bronchoalveolar carcinomas, 5 anaplastic cell carcinomas, and 9 adenosquamous carcinomas).
Laboratory examinations
After the decision for operation was made, first morning urine neopterin concentrations were determined by a high performance liquid chromatographic technique described earlier [14]. In brief, to compensate for physiologic variations in urine density, neopterin concentrations were adjusted according to creatinine, which was simultaneously determined. The native fluorescence of neopterin at 353 nm excitation wavelength and 438 nm emission wavelength was used for detection; creatinine was quantified from its ultraviolet (UV) absorbance at 235 nm [1]. Leukocyte and thrombocyte counts, hematocrit, hemoglobin, serum protein, serum urea, alkaline phosphatase, -glutamyl transferase, and aspartate aminotransferase at diagnosis were measured by routine techniques (data not shown). From these data and from the following routine checks, signs of infection in the patients could be excluded.
Statistical procedures
Patients were categorized into four classes of neopterin levels on the invariable basis of quartile points of the neopterin distribution. The postoperative survival of patients with preoperative neopterin values in the 4th quartile was compared with patients whose neopterin values were in quartiles 1 to 3. Other factors, such as T-stage status, grading, and nodal stages, were classified according to the TNM classification. The 
2 test was used to prove for the association of neopterin with survival expectation within the cohort of pathologic stage I. Univariate survival analyses were performed using the Kaplan-Meier product-limit estimation, including the generalized Savage test, according to Mantle-Cox test statistics [15, 16]. Values of p less than 0.05 were considered to be significant. For multivariate survival analyses, the proportional hazards technique was implemented according to the regression model by forward stepping of variables (Cox). Also for these analyses, neopterin was dichotomized on the basis of quartiles of the observed distribution. The calculations were performed by the software package SPSS/6.1.3 (SPSS Inc, Chicago, IL).
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Results
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Median preoperative urinary neopterin was 189 µmol/mol creatinine (5th to 95th percentile, 80 to 403; range, 58 to 715) with quartile points of 125, 167, and 212 µmol/mol creatinine. Accordingly, the cutoff value for survival analysis in this study was assessed by 212 µmol/mol creatinine. Twenty percent of the patients had elevated urinary neopterin concentrations according to the normal values assessed earlier [14]. Median neopterin values in T stages were T1, 156; T2, 197; T3, 209; and T4, 307. None of the patients with small cell lung cancer had a urinary neopterin level higher than 212 µmol/mol creatinine. For squamous cell carcinoma and adenocarcinoma, neopterin in the 4th quartile was significantly associated with worse survival (squamous cell carcinoma: p < 0.01, log rank 6.53; adenocarcinoma: p < 0.03, log rank 4.66). For other types of histology, the number of cases was too small to derive statistically unequivocal results. For nonsmall lung cancer, urinary neopterin more than 212 µmol/mol was significantly associated with early cancer death (p < 0.0001, log rank 16.09).
Of 110 patients, 75 (68.2%) patients were alive at the end of the study. Twenty-seven (24.5%) patients died of tumor progression. Eight patients (7%) died of other causes and were therefore excluded from the statistical calculations. After operation, 66 patients presented with pathologic status T1–T3N0. Of these patients, 11 had a neopterin level more than 212 µmol/mol creatinine; 9 patients in this group (82%) died of tumor progression after a median of 9 months (range, 1 to 44 months). In contrast, of 55 patients with pathologic stage T1–T3N0 cancer and neopterin less than 212 µmol/mol creatinine, only 11 patients (20%) died of tumor progression after a median of 20 months (range, 3 to 43 months) (2 according to Pearson: 16.60, p < 0.0001).
Univariate analysis of survival (Table 1) shows product-limit estimates of cumulative survival possibilities for patients according to clinical variables and preoperative neopterin concentrations in urine. For these estimates, neopterin concentrations were dichotomized on the basis of the cutoff point of 212 µmol/mol creatinine representing the 1st to 3rd and the 4th quartile, respectively, of the neopterin distribution. Neopterin more than 212 µmol/mol creatinine was found to be significantly associated with earlier tumor death. Among the clinical variables, T and nodal stage were significant predictors of survival. Figure 1 shows the computed cumulative actual survival curves of patients with preoperative neopterin concentrations less than 212 and more than 212 µmol/mol creatinine, respectively.
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Table 1. Results of Generalized Savage Test (Mantle-Cox Test) for Differences Between Cumulative Survival Probabilitiesa
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Fig 1. Product-limit estimates for cumulative survival probability for patients with lung cancer. Patients were dichotomized by urinary neopterin less than 212 µmol/mol (upper line) versus more than 212 µmol/mol creatinine (lower line). The circles symbolize censored cases.
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Table 2 shows the result of a multivariate survival analysis using the proportional hazards model. A stepwise regression including the significant variables from the univariate analysis, ie, nodal stage, neopterin in the 4th quartile, and T stage, was applied. In this model calculation, neopterin more than 212 µmol/mol creatinine and T stage turned out to have significant predictive value.
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Comment
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Elevated preoperative urinary neopterin concentrations are strongly associated with a worse prognosis in lung cancer [13]. T stage, lymph node status, and histologic criteria are the most common predictive variables for prognosis. However, a further variable is a desirable factor in thoracic operations. Currently in operations for lung cancer, the indication for lung resection is based mainly on clinical staging. In addition to clinical staging, based on CT and histologic results after mediastinoscopy, lung function tests and performance scores are important in the assessment for operation. Preoperative neopterin, as shown in our study, proved to be a very significant and particularly predictive variable for poor prognosis, independent of clinical staging. We therefore recommend neopterin detection in the preoperative evaluation of lung cancer patients. In patients with poor general health conditions high neopterin levels can help to decide for conservative treatment. Kronberger and coworkers [13] also found neopterin levels to be a significant predictive variable in lung cancer when all stages of lung cancer were included and some patients were treated by chemotherapy or radiation therapy alone. In our study, all patients had lung resection as primary therapy, and therefore clinical staging of the patients was mostly lower than stage IIIB. In contrast to other laboratory variables, which have practically no predictive value, neopterin turned out to be a significant and independent predictor of survival in carcinoma of the cervix uteri [9], ovarian carcinoma [8], prostatic carcinoma [10], hepatocellular carcinoma [12], and in squamous cell carcinoma of the oral cavity [17], in colon cancer [11], and in various hematologic neoplasias [18–20]. Studies in ovarian cancer investigating the predictive value of tumor markers and concomitantly measured neopterin showed that tumor markers are more strongly related to tumor load than to prognosis [21], whereas the current opinion in immunology is that neopterin reflects tumor–host interactions rather than quantity of tumor cells [13]. This is strongly supported by our results, which show that elevated neopterin is associated with early cancer death and worse prognosis even in small, node-negative lung cancers. Recent data show that neopterin is able to enhance reactions that are mediated by free radicals [22–25]. Activated macrophages achieve part of their cytotoxic activity by release of oxygen species. It is speculated that macrophages fine-regulate the production of free radicals by neopterin [13, 25], but the definitive relationship between rapid tumor progression and poor prognosis in cancer patients with elevated neopterin is still unknown. Neopterin is not produced by the tumor cells themselves and is therefore not a tumor marker in the common sense. Überall and colleagues [26] showed that neopterin and the reduced form of neopterin, 7,8-dihydroneopterin, enhance c-fos gene expression in rat NIH3T3 fibroblasts in vitro. We can conclude that tumor growth and development may be promoted by these compounds. Consequently, the prognostic value of elevated neopterin for prediction of rapid tumor growth may be attributed to the capacity of neopterin to induce oncogene expression [17].
For thoracic surgeons treating patients with lung cancer, detection of urinary neopterin can be helpful in decision making for surgical therapy. In patients with lung cancer we recommend considering preoperative neopterin as part of the surgical assessment. Exact pathologic staging, and consequently predictive information, is only available postoperatively. In contrast to all prognostic factors available today, neopterin detection is easily done and gives important and valuable prognostic information before surgical intervention is performed.
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Acknowledgments
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This work was financially supported by a grant from the Austrian Ministry of Science and Transport. All work was done at the Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz Pregl Strasse 3, A-6020 Innsbruck, Austria. We thank Katherine Hourmont, MD, for carefully reading the manuscript.
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Abstract
Introduction
