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Histological verification of positive positron emission tomography findings in the follow-up of patients with mediastinal lymphoma

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

Background and Objectives: Follow-ups of patients with mediastinal lymphoma are not accurate if they rely on computed tomography (CT). Positron emission tomography (PET) has been suggested to be useful in several lymphoma settings, such as initial staging, evaluation of residual masses after therapy, and assessment of response early in the course of treatment. The aim of this retrospective study was to verify the reliability of positive PET scans of the mediastinum in following up patients wirh mediastinal lymphoma, using histological findings as a comparison.

Design and Methods: From January 2002 to July 2005, 151 patients with mediastinal lymphoma (57 with Hodgkin’s disease [HD] and 94 with aggressive non-Hodgkin’s 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%). SUV_max 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.