Differentiation between rebound thymic hyperplasia and thymic relapse after chemotherapy in pediatric Hodgkin lymphoma
Friedrich Christian Franke, Adrian Damek, Jonas Steglich, Lars Kurch, Dirk Hasenclever, Thomas Georgi, Walther Alexander Wohlgemuth, Christine Mauz‐Körholz, Dieter Körholz, Regine Kluge, Judith Landman‐Parker, William H. Wallace, Alexander Fosså, Dirk Vordermark, Jonas Karlén, Ana Fernández‐Teijeiro, Michaela Čepelová, Tomasz Klekawka, Andishe Attarbaschi, Francesco Ceppi, Andrea Hrašková, Anne Uyttebroeck, Auke Beishuizen, Karin Dieckmann, Thierry Leblanc, Martin Moellers, Boris Buerke, Dietrich Stoevesandt
Abstract
BACKGROUND: Rebound thymic hyperplasia (RTH) is a common phenomenon caused by stress factors such as chemotherapy (CTX) or radiotherapy, with an incidence between 44% and 67.7% in pediatric lymphoma. Misinterpretation of RTH and thymic lymphoma relapse (LR) may lead to unnecessary diagnostic procedures including invasive biopsies or treatment intensification. The aim of this study was to identify parameters that differentiate between RTH and thymic LR in the anterior mediastinum. METHODS: After completion of CTX, we analyzed computed tomographies (CTs) and magnetic resonance images (MRIs) of 291 patients with classical Hodgkin lymphoma (CHL) and adequate imaging available from the European Network for Pediatric Hodgkin lymphoma C1 trial. In all patients with biopsy-proven LR, an additional fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT was assessed. Structure and morphologic configuration in addition to calcifications and presence of multiple masses in the thymic region and signs of extrathymic LR were evaluated. RESULTS: After CTX, a significant volume increase of new or growing masses in the thymic space occurred in 133 of 291 patients. Without biopsy, only 98 patients could be identified as RTH or LR. No single finding related to thymic regrowth allowed differentiation between RTH and LR. However, the vast majority of cases with thymic LR presented with additional increasing tumor masses (33/34). All RTH patients (64/64) presented with isolated thymic growth. CONCLUSION: Isolated thymic LR is very uncommon. CHL relapse should be suspected when increasing tumor masses are present in distant sites outside of the thymic area. Conversely, if regrowth of lymphoma in other sites can be excluded, isolated thymic mass after CTX likely represents RTH.