Definitive radiotherapy for early-stage follicular lymphoma: A retrospective study over two decades at a single institution

A BSTRACT Objectives: Follicular lymphoma is an indolent B-cell non-Hodgkin lymphoma that accounts for approximately 20%–30% of all non-Hodgkin lymphoma cases. Although definitive radiotherapy (RT) has historically been the standard treatment for limited-stage (I–II) follicular lymphoma, there are limited data on long-term outcomes beyond 10 years. Materials and Methods: Adult patients with stage I–II follicular lymphoma treated with curative-intent RT between September 2000 and October 2024 were retrospectively reviewed. The eligibility criteria included histologically confirmed follicular lymphoma (grade 1–3A), no bone marrow involvement, localized stage I–II disease, including extranodal stage IE/IIE gastrointestinal follicular lymphoma, at least 6 months of follow-up, and conventionally fractionated RT delivered at 1.5–2.0 Gy per fraction in more than 10 fractions. Results: Forty patients (median age, 62 years; range, 38–80 years) were included in this study. The median follow-up was 100.5 months (range, 9.2–265.0). The 5-, 10-, and 15-year overall survival (OS) rates were 97.1%, 97.1%, and 83.6%, respectively, and the corresponding progression-free survival (PFS) rates were 71.9%, 52.4%, and 39.3%, respectively. The median PFS was 174.0 months. The 10-year PFS did not differ significantly between patients with stage I (58.1%) and stage II (42.9%) ( P = 0.294). Fourteen patients relapsed, including three transformations to diffuse large B-cell lymphoma; no grade 3 or higher RT-related toxicities occurred. Conclusion: Treatment strategies incorporating definitive RT yielded excellent long-term OS and durable disease control in selected patients with localized stage I–II follicular lymphoma, including extranodal stage IE/IIE gastrointestinal follicular lymphoma, without high-grade toxicity. However, late relapse may occur after treatment, indicating the need for long-term surveillance.