Outcomes of the transformation of follicular lymphoma to diffuse large B‐cell lymphoma in the rituximab era: A population‐based study

Background Histological transformation (HT) to diffuse large B‐cell lymphoma (DLBCL) is a common complication of follicular lymphoma (FL) and is usually associated with a dismal outcome. However, the survival rate of these patients has improved over the last 20 years with the introduction of rituximab. This study aimed to access the outcome of transformation to DLBCL (t‐DLBCL) from FL in a retrospective series that began after the widespread use of rituximab use. In addition, we also compared survival between t‐DLBCL and primary DLBCL (p‐DLBCL) in the same timeframe. Methods We utilized the Surveillance, Epidemiology, and End Results (SEER) database to identify patients with primary FL and patients with p‐DLBCL between 2000 and 2020. Patients who had a subsequent diagnosis of DLBCL at least 2 months after FL diagnosis were identified as t‐DLBCL. Results Finally, we identified 50,332 FL and 95,933 p‐DLBCL. With a median follow‐up of 119 months, 1631 patients developed t‐DLBCL. The median time from FL diagnosis to t‐DLBCL was approximately 4 years. The post‐transformation survival (PTS) rate at 5 years was 49.6%, with a median PTS of 56 months. Older age, advanced stage, and early transformation were associated with worse PTS. Furthermore, t‐DLBCL receiving chemotherapy or combined modality as initial therapy before HT was also associated with worse PTS, while the result was inverse when taking the impact of initial management strategy at HT into account. Taking t‐DLBCL and p‐DLBCL as a whole, comparable survival was observed between p‐DLBCL and t‐DLBCL receiving radiation or watch‐and‐wait as initial therapy prior to HT. Conclusion The outcome of t‐DLBCL in the rituximab era was better than historical series before the rituximab era. Due to the good prognosis, we did not recommend autologous stem cell transplantation for t‐DLBCL receiving watch‐and‐wait or radiation as initial therapy before HT.