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Ann Thorac Surg 2004;77:259
© 2004 The Society of Thoracic Surgeons
Department of Thoracic and Vascular Surgery, University Hospital of Antwerp, Wilrijkstraat 10, B-2650 Edegem Belgium
e-mail: paul.van.schil{at}uza.be
Precise restaging after induction or neoadjuvant therapy is important to accurately determine response after chemotherapy or chemoradiotherapy and to decide on further treatment. This is especially relevant in patients with N2 disease as prognosis is poor in the case of persisting mediastinal involvement, and these patients will not benefit from surgical resection.
Classical imaging techniques as computed tomography (CT) and magnetic resonance imaging have a low accuracy in restaging the primary tumor and mediastinum. Initial reports on positron emission tomography (PET), which provides an image of metabolically active cells, were promising, and it was hoped that PET would accurately predict response after induction therapy. However, in subsequent studies, PET was found to accurately detect residual viable disease in the primary tumor but not in the mediastinal lymph nodes, which are the real focus of interest. These results are confirmed by the present prospective study of 25 patients, for whom the percent change in standard uptake value was calculated between pre- and postinduction PET scans. Unfortunately, two different chemotherapy regimens were used and there were only 7 patients who initially had N2 disease proven by mediastinoscopy. In predicting nodal stage, PET was not found to be more accurate than CT. For N2 disease, the positive predictive value of PET was less than 20%. As well, false-positive and false-negative rates were unacceptably high. What are the probable reasons for this? The interval between the end of chemotherapy and the post-induction PET scan was only 2 weeks. Residual inflammatory disease will remain visible on PET scan accounting for the high false-positive rate. A longer time interval will reduce this rate, but is less optimal when a surgical resection has to be planned. On the other hand, PET scan will not detect residual microscopic disease, explaining the high false-negative rate. Therefore, invasive staging remains necessary to accurately determine response after induction therapy.
Remediastinoscopy, although technically more difficult, is feasible and has an accuracy of 80% in recent series. Alternative approaches include endoscopic ultrasonography or ultrasonography-assisted bronchoscopy with transbronchial or transesophageal needle aspiration biopsy of suspicious lymph nodes. These can be performed at the initial staging; this way, mediastinoscopy can be reserved for after the induction therapy. However, these alternative techniques have a high false-negative rate and have not been properly validated at the present time.
The ideal noninvasive restaging method is not yet available. The results of PET scanning in restaging the mediastinal nodes are disappointing and only invasive staging will provide objective evidence of mediastinal downstaging.
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