Ann Nucl Med DOI 10.1007/s12149-014-0847-4

LETTER TO THE EDITOR

Is it time to validate the prognostic role of F-18-FDG PET/CT scan in thymic epithelial tumors? Filippo Lococo • Alfredo Cesario • Giorgio Treglia

Received: 8 February 2014 / Accepted: 13 February 2014 Ó The Japanese Society of Nuclear Medicine 2014

Sir, The conclusions drafted in the very interesting report from Seki and co-workers [1] on a retrospective analysis of a relative large series of patients with thymic epithelial neoplasms (TENs) imaged with 18F-FDG PET/CT prompted some reflections, discussed herein. The authors divided the population of study into 3 groups according to a simplified WHO-histologic classification: (a) ‘‘low-risk’’ thymoma; (b) ‘‘high-risk’’ thymoma and (c) thymic carcinoma. A correlation among the radiometabolic findings (tumor SUVmax) first with such histologic classification and, secondly, with recurrence-free survival has been detected. In fact 18F-FDG PET was proven to reflect TENs’ WHO classification. In this scenario, a certain body of evidence exists, and this supports the role of 18F-FDG PET/CT in discriminating WHO histologic subclasses of TENs [2–5]. Therefore, the results of Seki and colleagues are substantially in line with others. More interestingly, however, the authors have linked the 18F-FDG PET/CT findings with recurrence-free survival rate of the cases in study and observed that a SUVmax value C4.27 was significantly associated with a lower disease-free survival (and thus a potentially reliable predictor of tumor relapse). F. Lococo (&) Unit of Thoracic Surgery, IRCCS-Arcispedale Santa Maria Nuova, Reggio Emilia, Italy e-mail: [email protected] A. Cesario IRCCS San Raffaele Pisana, Rome, Italy G. Treglia Department of Nuclear Medicine and PET Center, Oncology Institute of Southern Switzerland, Bellinzona, Switzerland

The analysis performed by the authors is indeed remarkable; however, we would advocate a certain caution when considering the prognostic impact of 18FFDG PET/CT in these tumors. Our team has recently reported a retrospective multicentric study [6] on a relative large series of patients (47 cases) affected by TENs and imaged with 18F-FDG PET/CT. We have also reported similar results in terms of predictability of WHO malignancy grade of such tumors; in our analysis we did not investigate any possible association with the long-term results in such cohort of patients. Indeed, the mean follow-up time (about 24 months) of our study population did not allow any investigation on the prognosis of these subjects. In Seki’s report, we have no details on the mean follow-up time of the study. Given the time-span of the 7-year long enrollment period (from 01/06 to 12/12), the oncological follow-up surveillance was definitely too short to support any inference on the long-term outcome. In fact, it is definitely known [7] that thymic epithelial tumors are normally indolent and slow-growing neoplasms, with a limited recurrence rate and a very long mean diseasefree survival (recurrence time-span often lasting decades). When we have retrospectively analyzed our single-centre 40-year experience [8] in the management of patients with recurrent thymomas, we have observed a disease-free interval (defined as the period between initial tumor resection and the occurrence of tumor relapse) of 92.7 ± 77.8 months (range 8–390 months). These evidences support the consideration that, when evaluating the potential prognostic role of 18F-FDG PET/CT in TENs, a long-to-very-long follow-up of the cohort of study is mandatory. We would greatly appreciate the authors to discuss on the points raised.

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References 1. Seki N, Sakamoto S, Karube Y, Oyaizu T, Ishihama H, Chida M. 18F-Fluorodeoxyglucose positron emission tomography for evaluation of thymic epithelial tumors: utility for World Health Organization classification and predicting recurrence-free survival. Ann Nucl Med. 2014. (Epub ahead of print). 2. Treglia G, Spitilli MG, Calcagni ML, Giordano A. The role of nuclear medicine in the management of thymomas. Ann Ital Chir. 2007;78:371–4. 3. Kumar A, Regmi SK, Dutta R, Kumar R, Gupta SD, Das P, et al. Characterization of thymic masses using F18-FDG PET-CT. Ann Nucl Med. 2009;23:569–77. 4. Igai H, Matsuura N, Tarumi S, Chang SS, Misaki N, Go T, et al. Usefulness of F18-fluoro-2-deoxy-D-glucose positron emission tomography for predicting the World Health Organization malignancy grade of thymic epithelial tumors. Eur J Cardiothorac Surg. 2010. Online 15 Oct.

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5. Terzi A, Bertolaccini L, Rizzardi G, Luzzi L, Bianchi A, Campione A, Comino A, Biggi A. Usefulness of 18-F FDG PET/CT in the pre-treatment evaluation of thymic epithelial neoplasms. Lung Cancer. 2011;74(2):239–43. doi:10.1016/j.lung can.2011.02.018 Epub 25 Mar 2011. 6. Lococo F, Cesario A, Okami J, Cardillo G, Cavuto S, Tokunaga T, Apolone G, Margaritora S, Granone P. Role of combined 18F-FDGPET/CT for predicting the WHO malignancy grade of thymic epithelial tumors: a multicenter analysis. Lung Cancer. 2013;82(2): 245–51. doi:10.1016/j.lungcan.2013.08.003 Epub 13 Aug 2013. 7. Lococo F, Cesario A, Margaritora S, Granone P. Caveats in recurrent thymoma management. J Thorac Oncol. 2012;7(8):1207–8. doi:10. 1097/JTO.0b013e31825f790c no abstract available. 8. Margaritora S, Cesario A, Cusumano G, Lococo F, Porziella V, Meacci E, Evoli A, Granone P Single-centre 40-year results of redo operation for recurrent thymomas. Eur J Cardiothorac Surg. 2011;40(4):894–900. doi:10.1016/j.ejcts.2011.01.025. (Epub 25 Feb 2011. Erratum in: Eur J Cardiothorac Surg. 2012;41(3):727.