Invasive-field radiotherapy plus rituximab versus rituximab alone after response to immunochemotherapy in stage III follicular lymphoma: An open-label, multicenter, randomized clinical study.

7054 Background: Stage III follicular lymphoma (FL) remains incurable with immunochemotherapy followed by rituximab maintenance. Radiotherapy plays a critical role in the curative treatment of early-stage FL; however, its role in the management of stage III disease remains undefined. Methods: In this open-label, multicenter, randomized clinical trial, patients with stage III FL, who demonstrated complete or partial response without bulky after induction immunochemotherapy were enrolled. Eligible patients randomly assigned (1:1) to receive invasive field consolidation radiotherapy (IFRT) combined rituximab maintenance (IFRT+R arm) or rituximab maintenance alone (R arm). The dose of IFRT was 30Gy. The primary endpoint was 5-year progression-free survival (PFS), and the secondary endpoint was 5-year overall survival (OS). This study is registered with Chinese ClinicalTrials.gov, number ChiCTR2000032550. Results: Between January 2015 to January 2021, 152 eligible patients were randomly assigned to receive IFRT+R (n=74) or R alone (n=78). Baseline characteristics showed no significant differences between the two arms. After a median follow-up of 82 months, the 5-year PFS was 88.9% in IFRT+R group and 66.7% in R alone group (HR, 0.32; 95% CI, 0.16-0.66, P = 0.002). The 5-year OS was 97.3% in IFRT+R group versus 84.4% in R group (HR, 0.23; 95% CI, 0.07-0.81, P = 0.02). Treatment-related adverse events were more frequent in the IFRT+R arm than in the R arm (58% vs 38%), predominantly consisting of acute hematologic toxicities, including neutropenia (33% vs 26%) and leukopenia (34% vs 28%). Grade 3-4 toxicities were more common in the IFRT+R arm (27% vs 18%), and no treatment-related deaths were observed. Conclusions: Involved-field radiotherapy after effective systemic therapy significantly improved PFS and OS with manageable toxicity, highlighting its potential role in the management of stage III FL. Clinical trial information: ChiCTR2000032550.