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J Thorac Cardiovasc Surg 2006;132:763-768
© 2006 The American Association for Thoracic Surgery
General Thoracic Surgery |
a Thoracic Service, Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, New York.
b Nuclear Medicine Service, Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, New York.
c Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, New York.
d Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York.
Presented in part at the 39th American Society of Clinical Oncology meeting, Chicago, Illinois, May 31–June 3, 2003.
Received for publication November 25, 2005; accepted for publication March 21, 2006. * Address for reprints: Raja M. Flores, MD, Thoracic Service, Department of Surgery, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021. (Email: floresr{at}mskcc.org).
| Abstract |
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Methods: Patients with pathologically proven mesothelioma underwent fluorodeoxyglucose positron emission tomography scanning. Patients fasted and received a minimum of 10 mCi of F18-fluorodeoxyglucose. Whole-body emission studies were acquired, followed by whole-body transmission scans with iterative reconstruction. On the basis of the maximal chi-square method, a standard uptake value of 10 was chosen to classify patients as low versus high standard uptake value. Survival probabilities for both standard uptake value groups were estimated by the Kaplan-Meier method. A Cox proportional hazards model assessed the joint influence of standard uptake value, histology, and stage on survival.
Results: From 1998 to 2005, 137 patients with malignant pleural mesothelioma underwent positron emission tomography scans. The median follow-up for all surviving patients was 24 months. Median survivals were 9 and 21 months for the high and low standard uptake value groups, respectively (P = .02). In a multivariable analysis, high standard uptake value tumors were associated with a 1.9 times greater risk of death than low standard uptake value tumors (P < .01). Mixed histology carried a 2.9 times greater risk of death than epithelioid histology (P < .01), and stages III and IV had a 1.8 times greater risk of death than stages I and II (P = .05).
Conclusions: Standard uptake value greater than 10, mixed histology, and stages III and IV are poor risk factors in malignant pleural mesothelioma. These findings suggest that fluorodeoxyglucose positron emission tomography can be used to stratify patients for treatment and clinical trials.
| Introduction |
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We previously investigated positron emission tomography (PET) as a preoperative staging tool and found that it identified occult distant metastasis in 10% of patients, but that it did not predict T4 disease identified at surgery.3
However, a high PET standard uptake value (SUV) did correlate with the presence of N2 disease at the time of resection in MPM. Because SUV seems to reflect the tumor biology of MPM, we hypothesized that maximum PET SUV independently predicts survival in MPM.
The objectives of this study were to determine whether PET SUV predicted survival and to identify an SUV cutoff value that stratifies patients into high- and low-risk groups.
| Methods |
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PET Evaluation
PET scans were acquired on dedicated BGO-based systems, including the GE Advance (Munich, Germany, Siemens HR+, and Siemens Biograph scanners (Erlangen, Germany). All patients were instructed to fast for 6 hours before the administration of FDG. After a minimum of 45 minutes post-injection of at least 10 mCi of FDG, whole-body emission scans were performed, with rod source-based transmission scans to allow for iterative reconstruction with segmented attenuation correction.
Patients were clinically staged by PET with the American Joint Commission on Cancer and the Union Internationale Contre le Cancer staging system.4,5
The SUV was calculated according to standard methods based on the uptake of FDG in grams per milliliter corrected for the injected dose of FDG adjusted for the patient's weight. To calculate the maximal SUV in the tumor, we electronically threshholded the images so that only the hottest voxel of tumor was seen. A region of interest was drawn around the hottest voxel on the transaxial slice of the iteratively reconstructed images, and the SUV maximal value, corrected for body weight, was recorded.
Statistical Methods
A Wilcoxon test was used to compare the median SUV of the epithelioid and non-epithelioid tumor types. A hazard function plotting SUV versus predicted median survival time was constructed to visualize the functional relationship between SUV as a continuous variable and survival. The maximal chi-square method was used to identify an optimal SUV cutoff that separated patients into high- and low-risk groups.6
Kaplan-Meier analysis was first performed on patients grouped by the accepted predictors of survival (stage and histologic subtype) and then performed on patients grouped by low and high SUV. Finally, Kaplan-Meier survival probabilities were assessed on patients with epithelioid tumor histology for all the 4 possible categories by using SUV as a dichotomous variable (high and low), as well as stages I and II and stages III and IV.
A Cox proportional hazard analysis was used to identify predictors of survival. The initial model was performed including all known predictors of survival. Insignificant variables were then dropped using a stepwise procedure, thus yielding the final model.
| Results |
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Standard Uptake Value in Relation to Tumor Histology
The median SUV of the epithelioid tumors was 6.2, which was not significantly different from tumors of mixed histology for which the median SUV was 7.8 (P = .9). Four sarcomatoid tumors had a median SUV of 3.8 (Table 1).
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| Discussion |
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The first study included 22 patients with pathologically proven MPM.8
The goal of this study was to evaluate whether PET could help distinguish between benign and malignant pleural disease. PET demonstrated a sensitivity of 92% (22/24) and a specificity of 75% (3/4). SUV data were available in only 18 patients. A survival analysis was not performed. The main point was that differentiating benign from malignant pleural disease still required pathologic confirmation; however, PET did seem to be useful in guiding surgical biopsy.
In 1999 the same group evaluated the prognostic value of FDG PET in 17 patients who had both SUV data and a diagnosis of mesothelioma.9
A high SUV seemed to correlate with short survival in 6 deceased patients. However, surviving patients and a patient who died postoperatively were excluded from the analysis. Kaplan-Meier analysis using an arbitrary division at an SUV of 4 demonstrated a modest difference in survival; however, interpretation of these results is difficult because more than half (n = 9) of the patients in this series had non-epithelioid histology, which does not reflect the predominance of epithelioid histology among patients with mesothelioma. In addition, the majority of patients with a high SUV also had higher stage tumors and unfavorable histology (mixed or sarcomatoid). A multivariate analysis to control for the influence of treatment (surgical or medical), stage, and histology was not performed. Therefore, meaningful conclusions are difficult to draw from this study.
In 2000, Schneider and colleagues10
evaluated the utility of PET scan in 18 patients evaluated preoperatively. SUV data were available in only 9 patients. Two patients were excluded from surgery on the basis of extrathoracic disease. Although PET correctly identified 2 positive lymph nodes that were missed by CT scan, it falsely identified 2 nodes as being positive. This study did not evaluate the role of SUV in predicting survival, and the small number of patients limits the validity of the analyses.
In a previous article we reported scans between 1998 and 2002, 60 preoperatively and 3 to assess disease recurrence after surgery.3
Increased FDG uptake was seen in all but 1 tumor, which was very early stage disease (IA). PET findings yielded sensitivities of only 19% and 11% for tumor stage and nodal status, respectively. However, a high SUV in the primary tumor correlated with the presence of N2 disease. PET correctly identified supraclavicular N3 or M1 disease in 6 patients. Although PET did not reliably identify the local extent of tumor or mediastinal nodal metastases, extrathoracic metastases were identified in 10%, thereby obviating inappropriate thoracotomy.
Several other small studies exist that investigated the use of PET scanning in mesothelioma but focused primarily on staging rather than survival.11-13
Accurate patient selection for treatment has become increasingly important because of the development of improved chemotherapy regimens (eg, pemetrexed and cisplatin) and the need to decide which patients might benefit from induction therapy before resection. Our previous analysis in 63 patients showed a survival benefit for those with tumors with an SUV of less than 4. However, there were only 13 patients in this category.14
Our current study is more than double the size of the prior study, and a similar analysis suggests that an SUV of 10 is a more robust value to dichotomize patients into high and low groups. As greater numbers of patients are studied in the future it is possible that 3 values may be found to separate patients with mesothelioma by prognosis: an SUV less than 4 and greater than 4, and an SUV less than 10 and greater than 10.
The demographic data in this study are consistent with those usually observed in MPM: The majority of patients were male, and most tumors were of epithelioid histology. The differences in survival between epithelioid and non-epithelioid subtypes and among tumor stages are consistent with previously published data.15,16
We found no significant difference in the median SUV between epithelioid and non-epithelioid tumors. Although the median SUV of pure sarcomatoid lesions seems lower, there were only 4 such patients in this series (all in advanced stage). Indeed, a previous study of 17 patients with MPM reported 1 sarcomatoid tumor with an SUV of 8.25.8
Although there are too few patients with sarcomatoid MPM in this study to draw definitive conclusions regarding SUV levels in relationship to this histology, it seems that the SUV may reflect tumor biology independent of tumor histology.
PET SUV was not used to direct treatment; therefore, a selection bias based on SUV results should not exist. It seems that increasing SUV is a predictor of poor prognosis. This finding is not unexpected given the fact that SUV is a reflection of metabolic rate and nodal involvement, which usually correlates with more biologically aggressive tumors and poor survival. To date, histology and TNM stage have been the best predictors of survival. The final Cox model also revealed that patients with an SUV greater than 10 had a 1.9 times greater risk of death than those with an SUV less than 10, that non-epithelioid histology had a 2.8 times greater risk of death than epithelioid histology, and that stage III and IV tumors had a 1.8 times greater risk of death than stage I and II tumors. On the basis of these findings, it seems useful to stratify future clinical trials by SUV, histology, and stage.
| Conclusions |
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| References |
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