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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 Department of Endocrinology and Metabolism, Orthopaedics and Traumatology, Occupational Medicine, University of Pisa, 2 Pulmonary Unit, University Hospital of Pisa, Pisa, Italy; 3 Molecular Epidemiology, 4 Clinical Pathology, and 5 Epidemiology and Biostatistics, National Cancer Research Institute of Genoa, 6 Pulmonary Unit, 7 Medical Oncology, A.O. Villa Scassi Genoa, Genoa, Italy; 8 Pulmonary Unit, A.O. Sarzana, La Spezia, Italy; and 9 Department of Medicine, Local Health Unit 11, Vercelli, Italy
Requests for reprints: Alfonso Cristaudo, Departments of Endocrinology and Metabolism, Orthopaedics and Traumatology, and Occupational Medicine, University of Pisa, "Cisanello Hospital", Via Paradisa 2, Pisa 56124, Italy. Phone: 39-5099-3820; Fax: 39-5099-3822; E-mail: a.cristaudo{at}med.unipi.it.
| Abstract |
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Experimental Design: SMRP blood concentrations were measured in 107 patients with MM, 215 patients with LC, 130 patients with benign respiratory diseases (BRD), and 262 controls. Statistical comparison between mean serum SMRP levels in all groups was done and receiver operating characteristic curves were constructed to evaluate the performance of this marker.
Results: SMRP levels were significantly higher in patients with MM and LC than in patients with benign respiratory diseases and controls (P < 0.001). The area under the receiver operating characteristic curve for serum SMRP discriminating MM and controls was 0.77 (95% confidence interval, 0.71-0.83), with a best cutoff of 1.00 nmol/L (sensitivity, 68.2%; specificity, 80.5%). In both MM and LC, serum SMRP levels did not differ significantly between early and late stages. High SMRP levels proved to be an independent negative prognostic factor in patients with MM.
Conclusions: Our data confirm that serum SMRP is a promising marker for the diagnosis, prognosis, and clinical monitoring of MM. We found that serum SMRP dosage may prove helpful in LC diagnosis as well. These data may also have positive repercussions on secondary preventive medical strategies for workers previously exposed to asbestos.
Because of the widely exposed population, a secondary prevention strategy exclusively based on radiological examinations for MM is not very feasible from either an ethical or an economical point of view, whereas the advisability of radiological screening for LC is still a matter of debate. In fact, although it is indisputable that spiral CT screening can detect early stage LC, its effectiveness in reducing LC-related mortality has not yet been shown (9). Therefore, the investigation of biological markers as "risk factors" or "markers of early diagnosis" is strongly recommended by the scientific community (10, 11).
Recently, several authors have proposed mesothelin as a promising predictive marker for early evidence of MM (12–17). The human mesothelin gene codes for several proteins and is consistently expressed in normal mesothelial cells and even more in mesotheliomas, ovarian cancers, and pancreatic adenocarcinomas. The primary product of the gene is a 71-kDa precursor protein which undergoes physiologic cleavage by a furin-like protease resulting in two main proteins. One is the 31-kDa NH2-terminal megakaryocyte potentiation factor, which is normally secreted into the blood. The COOH-terminal product of the cleavage, a 40-kDa glycosylated phosphatidylinositol-linked glycoprotein, remains bound to the cell membrane and provides epitopes for immunohistochemistry. Some authors have suggested that after further subsequent cleavages, this cell surface protein releases soluble mesothelin-related peptides (SMRP), which are the principal mesothelin family proteins tested thus far (12–15). In order to evaluate its clinical (prognostic/diagnostic) significance, we assessed the level of serum SMRP in patients with MM and LC and in patients with benign pleural or lung diseases (benign respiratory diseases—BRD) and controls with or without a history of asbestos exposure.
| Materials and Methods |
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A questionnaire, elaborated by the Italian National Institute of Occupational Safety and Prevention, and aimed at assessing asbestos exposure level (classified as "ascertained", "probable", and "possible") as well as providing data regarding the history of previous diseases and dwellings, was administered by trained personnel either directly to each participant or to their relatives. Approval from the ethical boards and written informed consent was obtained from all participants.
SMRP dosage. Serum mesothelin concentrations were determined using Mesomark (by Cisbio International), following the manufacturer's instructions. SMRP assays were all done in a single laboratory ("Santa Chiara", Pisa University Hospital) by investigators who were unaware of the patients' diagnoses. All serum samples were analyzed in duplicate.
Statistics. SMRP levels were transformed into natural logarithms. Differences in the values between the groups studied were checked using independent samples test and ANOVA procedures. The univariate relation of each independent variable to the groups was examined using the
2 test. Pearson's correlation method was used to correlate the SMRP level with age.
In order to evaluate the performance of SMRP, receiver operating characteristic curves (18), areas under the receiver operating characteristic curves (AUC), and their 95% confidence intervals (95% CI) were calculated using standard techniques.
Logistic regression models were established to evaluate the power of the five cut-points considered to discriminate between cases and controls. Age, gender, and asbestos exposure were included in the models to adjust for the possible confounding effects. Akaike information criteria (19) was used to compare the goodness-of-fit of each model. The "optimal" cut-point was estimated through an "ad hoc" developed STATA routine (20, 21), and its 95% CI was computed by means of a bootstrap procedure (22). All other statistical tests were done by using SPSS for Windows.
Predictive values were estimated on the basis of the number of MM expected among the asbestos-exposed population according to the incidence rate in our geographic areas (two cases/10,000 person-years in the 55-65 years old age groups) increased 5-fold due to asbestos exposure (10 cases/104 person-years).
In order to evaluate the SMRP prognostic significance on survival of patients with MM, Cox's proportional hazards regression analysis (21) was carried out as multivariate analysis, adjusting for age, sex, histology, platelet count, treatments (chemotherapy, radiotherapy, or surgery), and clinical stage (according to the International Mesothelioma Interest Group staging system). Survival time was calculated from the date the serum sample was obtained. Survival curves were determined using the Kaplan-Meier method. The log-rank test allowed us to evaluate the differences between survival curves.
| Results |
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SMRP was higher in epithelioid than in sarcomatous mesothelioma (P = 0.01), whereas the desmoplastic type showed the lowest levels in comparison with other groups (P = 0.04 versus epithelioid and P = 0.05 versus mixed tumors; Table 2). Differences in SMRP levels between the early and late stages of MM were evident, although not statistically significant (Table 2).
The receiver operating characteristic curves showing the performance of SMRP in discriminating between either thoracic cancers and BRD or controls were comparable, so comparisons were made between MM (Fig. 2A ) or LC and the latter group. The AUC value was 0.77 for both groups of MM regardless of the stage (95% CI, 0.71-0.83) and for patients with stage I to II disease (95% CI, 0.68-0.89; Fig. 2B). In patients with stage III to IV MM, the AUC value was 0.81 (95% CI, 0.72-0.90). AUC was 0.81 (95% CI, 0.75-0.88) in epithelioid or mixed MM and 0.62 (95% CI, 0.40-2.85) in the sarcomatous type.
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SMRP and survival in MM. Most of the patients with MM (101) were followed up. During the study period, 69 patients (68.3%) died. Median follow-up time was 6 months (range, 0.30-57.6 months) and 9.4 months (range, 0.4-51.7 months) for censored and deceased patients, respectively. In agreement with the literature (23), median survival time for the entire group was 13 months. Median survival of patients was 21.5 months (for patients with MM) and 9.8 months (for patients with SMRP), lower and higher than the assumed cutoff of 1 nmol/L, respectively (P < 0.001; Fig. 3 ).
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400 103/µL; HR, 2.32; 95% CI, 1.47-3.67; P < 0.001), age (
68 versus <68 years; HR, 1.50; 95% CI, 1.04-2.18; P = 0.03) was found. Interestingly, SMRP levels above the assumed cutoff of 1 nmol/L were found to be independent predictors of poor survival (HR, 1.62; 95% CI, 1.10-2.39; P = 0.02). SMRP levels in LC. The log of the SMRP mean values were also significantly higher in patients with LC than in patients with BRD (P = 0.001) or controls (P < 0.001).
Contrary to what was observed in patients with MM, SMRP dosage in LC was not related to histology. No significant difference in SMRP levels was found among different stages of LC (Table 2).
The efficacy of SMRP in discriminating between LC and BRD was 52%. AUC was 0.58 (95% CI, 0.52-0.64). Although associated with a high specificity (79.0%), the sensitivity was low (33.0%).The efficacy of SMRP in discriminating between LC and controls was 59.0%. AUC was 0.62 (95% CI, 0.56-0.68), the specificity was 80.2% and the sensitivity was 33.5%.
| Discussion |
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With regard to the comparison between patients with MM and controls, we found that the cutoff of 1 nmol/L is associated with a sensitivity of 68.2% and a specificity of 80.5%. Comparing MM and BRD, the specificity was very similar (80.8%).
Robinson et al. (15), comparing 48 patients with MM with 40 asbestos-exposed healthy controls, found a sensitivity of 83% (40 out of 48 patients) and a specificity of 82.5% (33 of 40). Hassan et al. (13), using a different method, observed higher SMRP levels with respect to 24 healthy volunteers and 95 random hospital patients, in 40 out of 56 patients with MM (sensitivity, 71%; specificity, 88% versus hospital patients). Recently, in 74 patients with MM versus 28 patients with benign pleural lesions associated with asbestos exposure, Scherpereel et al. (14) identified a cutoff of 0.93 nmol/L, which allowed the differentiation of MM from benign pleural diseases, with a sensitivity of 80% and a specificity of 82.6%. To date, the difference in mesothelin sensitivity and specificity observed in different studies may reflect differences in methods used or in the size of the populations studied. Both Robinson's and Hassan's groups data were obtained by a self-arranged method of analyzing mesothelin, whereas Scherpereel et al. used the same kit that we did (Mesomark).
In our study, no asbestos exposure effect was observed on SMRP levels in all the categories of patients considered. Furthermore, our results suggest that the presence of very high levels of SMRP (>2.4 nmol/L) may be an additional useful tool for MM diagnosis in those difficult cases with lung abnormalities and previous asbestos exposure, when in clinical experience, the advisability of thoracoscopy is often doubtful. Of the 392 patients included in the study who did not suffer from any kind of tumor, neither controls nor patients with BRD presented SMRP levels higher than 2.4 nmol/L. It was observed (12, 13) that SMRP decreases after a surgical debulking procedure, whereas it tends to remain stable in patients who did not respond to chemotherapy, this suggests that SMRP may be a useful marker for monitoring response to treatment, although no previous publications have described a correlation with patient survival. Interestingly, in our study, the results of the Cox's regression analysis indicated that the SMRP concentration is also a significant independent prognostic factor. In fact, median survival of patients with MM was 11.7 months longer for patients with SMRP levels lower than the assumed cutoff of 1 nmol/L compared to those with higher SMRP levels. This is the first evidence that SMRP levels can play this prognostic role in patients with MM. This provides clinicians with an opportunity to consider this test a novel tool for achieving better prediction of tumor aggressiveness in patients with previously histologically demonstrated MM, regardless of its stage.
Mesothelioma is characterized by a long latency period in spite of its rapid, aggressive clinical outcome. Therefore, effective preventive protocols may include very frequent instrumental diagnostic tests done over a long period of time, i.e., decades, which may be neither economical nor ethical. Consequently, the use of early high-sensitivity/high-specificity diagnostic markers is strongly recommended.
In agreement with data previously obtained by other authors (12–17), our findings indicate that SMRP may be a useful marker in the periodic surveillance of individuals previously exposed to asbestos.
The choice of the best cutoff level for clinical practice as well as for surveillance of exposed workers is a crucial point. A highly sensitive cutoff would be responsible for a high number of false-positives, and consequently, a high number of unnecessary potentially harmful radiological tests. On the contrary, a more specific cutoff would reduce the sensitivity. In addition, even with very high levels of sensitivity and specificity, none of these markers could reach a satisfactory positive predictive value for a rare tumor such as mesothelioma. As far as the clinical use of mesothelin dosage in LC is concerned, a few considerations are worth noting. Mesothelin showed a good performance in discriminating between LC and controls or BRD (80.2% and 79.0% of specificity), as well as between MM and LC (68% of specificity). These data suggest that serum mesothelin, together with other exams, may prove helpful in some difficult differential diagnoses (i.e., involving LC versus MM). On the other hand, the ability of the test to detect LC at a cutoff of 1 nmol/L was relatively poor (33% sensitivity) so the feasibility of serum mesothelin dosages in LC screening cannot be proposed. Nevertheless, we believe that among individuals previously exposed to asbestos, those with higher levels of serum SMRP might represent a subgroup at higher risk for either LC or even more so, MM. Therefore, this subgroup at higher risk may need a dedicated medical follow-up (i.e., more frequent diagnostic exams). Currently, further ongoing studies on a larger population are attempting to determine the most appropriate SMRP cutoff to be applied when screening subjects who have been exposed to asbestos.
On the whole, our findings provide evidence that high SMRP dosages can be considered an independent negative prognostic tool for patients with MM. Moreover, they suggest that this test could be helpful for both clinical and preventive purposes.
| Acknowledgments |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 3/19/07; revised 6/15/07; accepted 6/22/07.
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inhibits asbestos-induced cytotoxicity via a NF-
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U. Donatella, N. Monica, C. P. Aldo, C. Cristina, C. Giuseppe, I. G. Paolo, L. Cecilia, M. Paola, P. Michela, P. Barbara, et al. The CREST Biorepository: A Tool for Molecular Epidemiology and Translational Studies on Malignant Mesothelioma, Lung Cancer, and Other Respiratory Tract Diseases Cancer Epidemiol. Biomarkers Prev., November 1, 2008; 17(11): 3013 - 3019. [Abstract] [Full Text] [PDF] |
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