Malignant Lymphomas |
From the Institute of Hematology and Oncology "L. and A. Seràgnoli", University of Bologna (PLZ, MT, VS, LA, EM, MF, CP, MB); Nuclear Medicine, S. Orsola Hospital, University of Bologna (SF, PC, MF); Unité de Chirurgie Thoracique, Université Paris V, Hotel Dieu, Paris France (MA); Department of Pathology, Maggiore Hospital, Bologna (AC); Unit of Radiology, Bellaria Hospital, Bologna (GD); Chair of Radiology, University of Bologna (RC); Division of Thoracic Endoscopy and Pulmonology, Maggiore Hospital and Bellaria Hospitals, Bologna (RT); Division of Thoracic Surgery, Maggiore Hospital and Bellaria Hospital, Bologna, Italy (AB, MB)
Correspondence: Pier Luigi Zinzani, M.D., Istituto di Ematologia e Oncologia Medica "L. e A. Seràgnoli" Via Massarenti 9, 40138 Bologna, Italy. E-mail: plzinzo{at}med.unibo.it
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Design and Methods: From January 2002 to July 2005, 151 patients with mediastinal lymphoma (57 with Hodgkins disease [HD] and 94 with aggressive non-Hodgkins lymphoma [NHL]) were followed-up after the end of front-line treatment. Patients with a positive PET scan of the mediastinum underwent CT scanning and surgical biopsy.
Results: In 30 (21 HD and 9 NHL) out of 151 patients (20%) a suspicion of lymphoma relapse was raised based on positive mediastinal PET scanning. Histology confirmed this suspicion in 17 (10 HD and 7 NHL) out of 30 patients (57%), whereas either benign (9 fibrosis, 3 sarcoid-like granulomatosis) or unrelated neoplastic conditions (1 thymoma) were demonstrated in the remaining 13 patients (43%). SUVmax was significantly higher among patients who had signs of relapse (17 true positive cases) than among those who stayed in remission (13 false positive cases), the median values being 5.95 (range, 3.5–26.9) and 2.90 (range, 1.4–3.3), respectively (p=0.01).
Interpretation and Conclusions: We suggest that a positive PET scan of the mediastinum of a patient being followed-up for a mediastinal lymphoma should not be considered sufficient for diagnostic purposes in view of its lack of discrimination. Histological confirmation can safely be carried out with various biopsy techniques, the choice of which should be made on the basis of the findings of the clinical and imaging studies of the individual case.
Key words: PET, biopsy, mediastinal lymphoma, follow-up, CT scan.
In the last few years, fluorodeoxyglucose (FDG)-positron emission tomography (PET) has shown a number of potential advantages in refining and improving the management of Hodgkins disease (HD) and aggressive non-Hodgkins lymphoma (NHL). PET, a functional form of imaging based on the increased glucose metaobolism of tumor cells, plays a significant role in the initial staging,1–4 in the evaluation of residual masses after therapy,5–9 and in the monitoring of therapy response early in the course of treatment regimens.10–15 In all these clinical settings, the accuracy of PET in monitoring the response to treatment has proven superior to that of conventional computed tomography (CT). Another important field of application is the medium-and long-term follow-up of HD and aggressive NHL with mediastinal involvement at diagnosis, after complete response has been achieved. The role of PET can be decisive in early identification of mediastinal relapse, as the reliability of CT in differentiating between fibrotic tissue and active tumor is inadequate.10,16,17 In many centers, positive PET is among the main findings on which the decision to diagnose lymphoma relapse in the mediastinum rests, but no studies to date have verified the reliability of positive PET by comparing it with histological findings (the gold standard) in a consistent case series within this setting. The aim of the present retrospective study was to evaluate the specificity of PET in patients with suspected relapse of lymphoma, through comparison of positive PET with histological findings in a series of patients with suspected mediastinal relapse of either HD or NHL.
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Table 1. Clinical characteristics of the 151 patients with mediastinal lymphoma.
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3cm close to the chest wall.18,19 Video-mediastinoscopy (Richard Wolf GmbH, Knittlingen, Germany) was utilized for sampling paratracheal and hypocarinal pathologic nodes at imaging.20,21 Prevascular mediastinoscopy was used to sample retrosternal lymph nodes or lesions in the absence of significant fibrosis.21 Extended video-mediastinoscopy was proposed to sample prevascular lymph nodes and subaortic lymph nodes as an extension of conventional mediastinoscopy.22 Anterior mediastinotomy was utilized for sampling tissue in the anterior mediastinum close to the chest wall or deep as the hilum.23 Cervicotomy + manubriotomy (sternal split) was performed to gain access to retrosternal structures, mainy in the presence of fibrosis. It was considered elective for the radical removal of thymus and anterior mediastinal fatty and lymph node tissue.23,24 Video-thoracoscopy (VATS) was used for lesions of the hilum and/or those close to the mediastinal pleura, mainly when fine surgical dissection was expected, or another morbid condition of the pleura and/or lung had to be treated.23,25,26 Standard thoracotomy, which is the gold standard for major surgery of the lung and some mediastinal resections, was performed in cases for which a mini-invasive approach was considered inadequate. Frozen sections were always available to assess the nature of the tissue and eventually the quality of the sample. In this series, as usual, the least invasive biopsy technique was selected on the basis of imaging. When a procedure was considered unsatisfactory or risky, the least invasive enlargement or more aggressive technique was applied. All interventions were performed by the same team (MB, MA, SFP).
PET scans
PET scans for restaging were was performed 1 month after the end of chemotherapy and 3 months after completion of radiotherapy.
To optimize FDG uptake in normal and neoplastic tissue, patients were asked to fast for at least 6 h before undergoing the PET examination; no patient had a history of diabetes. FDG was produced in our radiopharmacy using standard synthesis techniques. Each patient was injected i.v. with about 6 MBq/kg of FDG; the PET scanning was carried out 70–90 min after injection of the tracer. Before PET scanning, patients were encouraged to void in order to minimize radioactivity in the bladder. FDG-PET scans were carried out using a dedicated tomograph (Advance NX, General Electrics Medical Systems, Milwakee, USA). Emission scans were acquired for 4 min at every table positron; 2-min transmission scans were also recorded in all patients. In all, about six bed positions were required for each patient, with a total scanning time of about 40 min. Images were reconstructed by segmented attenuation correction. PET images were evaluated by visual inspection and semi-quantitative analysis performed by three experienced readers. Standardized uptake values (SUV) were, in all cases, available to readers at the moment of reporting. Nonetheless PET scans were not categorized on the basis of a threshold SUV value, but by taking into account all available data, and in particular the site and degree of FDG accumulation.27 Areas of focal increased uptake were interpreted as suspicious of lymphoma unless they were at sites of known accumulation, including the kidney and bladder, gastrointestinal tract; skeletal areas showing symmetrical joint uptake (especially within the shoulder) were considered as due to arthritis.
PET evaluations were scored as negative or positive.28 Negative scans were defined as those showing no focal uptake that could be evidence of disease; positive scans were defined as those showing increased uptake possibly indicative of malignant disease. Thus for the purposes of the present study uncertain findings and findings suggestive of minimal residual disease were also considered as positive. Also, when areas of abnormal FDG uptake were identified, the intensity of FDG uptake was quantified by calculating the SUV. For the calculation of SUV, circular regions of interest (
70 pixels) were drawn on transaxial images around the areas with increased FDG uptake; the highest SUV measured was the one used (SUVmax).
Histological preparations
All specimens were formalin-fixed and paraffin-embedded, after which 3-mm thick sections were cut and stained with hematoxylin and eosin (H&E). Additional sections were obtained for histochemical study and immunophenotypic analysis, which were performed according to the avidin-biotin peroxidase complex method and by applying a panel of antibodies including the key-markers listed in the WHO classification.29 All histological examination were performed sequentially by two histopathologists (AC and SP).
Statistical methods
Data from the two groups were compared using the
2 test for categorical data (SUVmax data).30,31
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![]() View larger version (45K): [in a new window] [Download PPT slide] |
Figure 1. FDG PET showing an area of increased uptake in the mediastinum (A). The corresponding CT (after 7 days) was reported as negative for active disease (B).
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View this table: [in a new window] [Download PPT slide] |
Table 2. Clinical characteristics of the 17 patients with lymphoma relapse.
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Table 3. The different diagnoses obtained using various surgical techniques in the four imaging subgroups.
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The present PET-based follow-up analysis suggests that the specificity of PET in patients with suspected mediastinal relapse of lymphoma after front-line treatment is not optimal and that histological confirmation should be obtained whenever possible in order to choose the correct and reliabe therapeutic approach. In the present series mediastinal relapse of lymphoma, suspected from PET scanning results, was actually not confirmed by histology in 13 out of 30 patients (43%). It should be emphasized that we used PET positivity criteria designed to maximize sensitivity for the detection of relapse. Thus all non-negative PET findings were regarded as suspicious of viable tumor, which meant including patients with minimal residual disease in the PET-positive group. HD patients with minimal PET findings have already been reported to have a good prognosis.36 The reported prognostic value of interim FDG-PET after two or three cycles of chemotherapy in HD36 and our study support the hypothesis that such cases may be considered similar to patients in complete remission.
Compared to other studies, we found a relatively lower specificity for FDG PET. There are two main reasons for this difference: a) criteria used to score PET as positive (as just described) and b) criteria for including patients in the studies. With regards to the population studied, we excluded from further evaluation patients with PET findings at additional sites apart from the mediastinum. The extent of PET positivity is clearly related to the likelihood of relapse, so that the exclusion of such cases probably led to a decrease in the true positive rate of our PET findings.
Our study also suggests that reliable histological confirmation can be obtained in this setting with low morbidity, provided that the timing and the type of biopsy technique is chosen appropriately, taking into account the clinical and imaging findings of the individual patient. We employed several different surgical techniques ranging from the least invasive technique of needle biopsy to radical removal of tissue through extensive sampling. In detail, in this series, 24 biopsy procedures were mini-invasive, and seven were performed through a sternal split, which can be considered a mini-invasive technique in view of the minimal trauma, pain and hospital stay. It should be noted that even difficult biopsies, such as those performed in the presence of mediastinal fibrosis, which is constantly present in these patients, can be carried out in the large majority of cases through a mini-invasive approach. Only two biopsies were performed following a thoracotomy: in one case we performed radical resection of a fibrotic mass, and in another de-bulking was attempted but not carried as it would have required full-scale pneumonectomy, which was deemed excessive.
All nine diagnoses of fibrosis were made on very large specimens from patients who had substantial excision of pathologic tissues. The minimal amount and site of tissue to be sampled in order to yield a diagnosis of fibrosis is still an open issue: in this series frozen sections were used in seven cases to assess the nature of the tissue and, in some cases, the quality of the sample; when these were found not to indicate relapse, extensive sampling of presumed fibrotic tissue was carried out. Following diagnosis of thymoma, radical removal of a 5-cm mass was subsequently performed through an open chest procedure.
The occurrence of sarcoidosis and sarcoid-like reactions has already been reported in patients with both HD and NHL, these being secondary reactions to tumor antigens and/or immunological aberrations triggered by chemotherapeutic agents as the likely pathogenetic events.38,39
In no case was repeat surgery necessary: the two extended mediastinoscopies in which the sampling was deemed unsatisfactory were easily enlarged through a sternal split in the course of the same anesthesia.
In conclusion, the present study suggests that positive PET in the mediastinum of a patient being followed-up for a mediastinal lymphoma (hence after front-line treatment) should not be considered sufficient for final diagnostic purposes. Histological confirmation can be safely obtained by various biopsy techniques, the choice of which should be made on the basis of the clinical and imaging study findings of the individual case.
PLZ and MB contributed to the design, conduction and analysis of the study and wrote the paper; MT, RT, SF, VS, MA, PC, GM, GD, LA, EM, MF, CP, AC, AB, RC and SP performed the research and collected data; SP and MB critically reviewed the manuscript.
The authors reported no potential conflicts of interest.
Funding: this study was partially supported by BolognAIL.
Received for publication September 21, 2006. Accepted for publication March 14, 2007.
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