Omission of Radiotherapy in Primary Mediastinal B-Cell Lymphoma: IELSG37 Trial Results.

Martelli, Maurizio; Ceriani, Luca; Ciccone, Giovannino; Ricardi, Umberto; Kriachok, Iryna; Botto, Barbara; Balzarotti, Monica; Tucci, Alessandra; Usai, Sara Veronica; Zilioli, Vittorio Ruggero; Pennese, Elsa; Arcaini, Luca; Dabrowska-Iwanicka, Anna; Ferreri, Andrés Jm; Merli, Francesco; Zhao, Weili; Rigacci, Luigi; Cellini, Claudia; Hodgson, David; Ionescu, Codruta; ... (2024). Omission of Radiotherapy in Primary Mediastinal B-Cell Lymphoma: IELSG37 Trial Results. (In Press). Journal of clinical oncology(JCO2401373), JCO2401373. American Society of Clinical Oncology 10.1200/JCO-24-01373

Text martelli-et-al-2024-omission-of-radiotherapy-in-primary-mediastinal-b-cell-lymphoma-ielsg37-trial-results.pdf - Accepted Version Restricted to registered users only until 19 August 2025. Available under License Publisher holds Copyright. Download (4MB)

BACKGROUND

The role of consolidation radiotherapy in primary mediastinal B-cell lymphoma (PMBCL) patients is controversial.

METHODS

The IELSG37 trial, a randomized non-inferiority study, aimed to assess whether irradiation can be omitted in PMBCL patients with complete metabolic response (CMR) after induction immunochemotherapy. Primary endpoint was progression-free survival (PFS) at 30 months post-randomization. Patients with CMR were randomly assigned to observation or consolidation radiotherapy (30 Gy). With a non-inferiority margin of 10% (assuming a 30-month PFS of 85% in both arms), a sample size of 540 patients was planned with 376 expected to be randomized.

RESULTS

The observed events were considerably lower than expected, therefore, primary endpoint analysis was conducted when ≥95% of patients were followed for ≥30 months. Of 545 patients enrolled, 268 were in CMR after induction and were randomized to observation (n=132) or radiotherapy (n=136). The 30-month PFS was 96.2% in the observation arm and 98.5% in the radiotherapy arm, with a stratified hazard ratio of 1.47 (95%CI, 0.34 to 6.28) and absolute risk difference of 0.68% (95%CI, -0.97% to 7.46%). The 5-year overall survival was 99% in both arms.Non-randomized patients were managed according to local policies. Radiotherapy was the only treatment in 86% of those with Deauville score (DS) 4 and in 57% of those with DS 5. The 5-year PFS and OS of patients with DS 4 (95.8% and 97.5%, respectively) were not significantly different from those of randomized patients. Patients with DS5 had significantly poorer 5-year PFS and OS (60.3% and 74.6%, respectively).

CONCLUSIONS

This study, the largest randomized trial of radiotherapy in PMBCL, demonstrated favorable outcomes in patients achieving CMR with no survival impairment for those omitting irradiation.

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