Phase III Clinical Trials in First-Line Follicular Lymphoma: A Review of Their Design and Interpretation.

Follicular lymphoma (FL) is one of the most common subtypes of non-Hodgkin lymphoma worldwide. Improved survival outcomes with rituximab-based therapy in clinical trials led to the establishment of rituximab-based immunochemotherapy as standard of care for first-line (1L) treatment of FL. In the GALLIUM trial, obinutuzumab-based immunochemotherapy demonstrated improved progression-free survival (PFS), prolonged time-to-next antilymphoma treatment (TTNT) and comparable overall survival (OS) compared with rituximab-based immunochemotherapy as 1L treatment for FL. Using GALLIUM as an example, this article aims to explain how improved outcomes in 1L treatment of FL have changed the landscape for the design and interpretation of future trials. As approved therapies for 1L FL already achieve good responses, it is becoming more difficult to design trials that demonstrate further treatment benefits with the currently accepted primary endpoints. New endpoints are needed to reflect the long remission times, low relapse rates, and impact of subsequent therapies in FL. PFS is used as a primary efficacy endpoint in registrational clinical trials for indolent malignancies like FL, where improvement in OS is not always observed due to the large number of patients and long study duration required to demonstrate a clear survival benefit. However, there are limitations to using PFS as the primary endpoint. Other potential endpoints, including TTNT, progression of disease within 2 years, response rate, and minimal residual disease status are explored.