Role of radiotherapy and dose-densification of R-CHOP in primary mediastinal B-cell lymphoma: A subgroup analysis of the unfolder trial of the German Lymphoma Alliance (GLA).
Authors: Gerhard Held, Lorenz Thurner, Viola Poeschel, Christian Berdel, German Ott, Christian Schmidt, Andreas Viardot, Peter Borchmann, Ofer Shpilberg, Maike Nickelsen, Massimo Federico, Peter de Nully Brown, Niels Murawski, Lorenz H. Trumper, Heinz Schmidberger, Christian Ruebe, Jochen Fleckenstein, Norbert Schmitz, Markus Loeffler, Marita Ziepert
Journal: Journal of Clinical Oncology (2020)

8041 Background: Primary mediastinal B-cell lymphoma (PMBCL) is a distinct entity of aggressive lymphoma, which typically presents in young patients (pts) with a bulky mediastinal mass. Therapy is based on R-CHOP or similar regimens, but the role of treatment intensification and consolidative radiotherapy (RT) is controversial, because data from randomized trials are rare. Methods: The UNFOLDER trial included 18-60 year-old pts (aaIPI = 0 with Bulk [≥7.5 cm] or aaIPI = 1) qualifying for radiotherapy to Bulk or extralymphatic involvement (E). Pts were randomized in a 2 x 2 factorial design to 6xR-CHOP-14 or 6x-R-CHOP-21 without RT or with RT (39.6 Gy) to Bulk and E. Primary endpoint was event-free survival (EFS), secondary endpoints were progression-free (PFS) and overall survival (OS). Response was evaluated by the Internat Standardized Response Criteria, Cheson 1999. Results: 131 PMBCLs were included with a median age of 34 years, 54% were female, 79% had elevated LDH &gt; UNV and 24% had E. 82 pts (R-CHOP-21: 43; R-CHOP-14: 39) were assigned to RT and 49 (R-CHOP-21: 27, R-CHOP-14: 22) to no-RT. 96% (79/82) received RT per protocol and 5 pts in the no-RT arm received unplanned RT (4 after PR and 1 after CR/CRu). Response RT vs no-RT were CR/Cru 94% vs 84%, PR 2% vs 10%, PD 2% vs 4%. 3-year EFS was superior in pts assigned to RT (94% vs. 78%; p = 0.007), mostly due to events caused by initiation of RT (n = 5) in the no-RT arm. In an as treated analysis the difference between the RT and the no-RT arm was not significant (p = 0.136). Regarding PFS and OS no difference between the RT vs no-RT arm was detected (PFS: 95% (95% CI: 90-100) vs 90% (95% CI: 81-98), p = 0.253; OS: 98% (95% CI: 94-100) vs 96% (95% CI: 90-100), p = 0.636). Dose-densification of R-CHOP-21 by R-CHOP-14 did not improve EFS, PFS nor OS. Only 4 pts died. Conclusions: To our knowledge, this is the largest series of PMBCLs so far, which have been treated in a prospective, randomized trial in the rituximab era. The results reveal no differences between R-CHOP-14 vs R-CHOP-21. Pts assigned to RT had a superior EFS mostly due to a higher PR rate in the no-RT arm triggering RT, with no differences in PFS and OS. The results suggest a benefit of RT only for pts, who are responding to R-CHOP with PR. Testing RT in PET-positive residual tumors in a randomized trial can solve the question, while RT in PET-negative pts is studied in the ongoing randomized IELSG 37 trial. Our results indicate a very favorable 3-year OS of 96% in PMBCL pts treated with R-CHOP. Supported by Deutsche Krebshilfe, Amgen and Roche. Clinical trial information: NCT00278408 .