Maximum disease diameter is associated with outcomes in stage II follicular lymphoma treated with radiation therapy alone.

Purpose: The optimal management of stage II follicular lymphoma (FL) is unclear. Radiation therapy (RT) alone has been the gold standard treatment, but a proportion of patients relapse. We sought to characterize outcomes and prognostic factors for stage II FL treated with RT alone to identify a high-risk subgroup of patients who may benefit from treatment intensification. Methods: This was a population-based, province-wide, retrospective study. Included patients had grade 1-3A, non-mesenteric, stage IIA or IIAE FL diagnosed between 1986 and 2016 and treated with curative-intent (≥20 Gy) RT alone. Results: 102 patients were included. Median follow-up was 10.4 years (range, 0.3-22.3). Median age was 59 years (range, 33-86). Median greatest disease diameter was 3.6 cm (range, 1.5-11.5). Freedom from progression (FFP) was 60.3% at 5 years and 40.7% at 10 years. Overall survival (OS) was 89.2% at 5 years and 81.8% at 10 years. Greatest disease diameter of >3.6 cm was associated with inferior FFP (10-year FFP 34% vs. 47%, Conclusions: 40.7% of stage II FL patients treated with RT alone remained disease-free at 10 years. Greatest disease diameter >3.6 cm was associated with inferior FFP and OS, representing a novel prognostic indicator in this population that may help in the decision-making process on whether to complement RT with systemic therapy.