ACTR-24. THE ESTIMATED LONG-TERM SURVIVAL BENEFIT OF ADDING TTFIELDS TO THE STANDARD OF CARE FOR GLIOBLASTOMA PATIENTS

Abstract

BACKGROUND: Glioblastoma (GBM) is the most aggressive form of primary brain cancer. The EF‐14 trial for GBM patients reported a 5‐year survival rate of 12.8%, the first report from a large randomized controlled trial of 5‐year survival greater than 10%. The increased survival compared to previous studies was achieved by adding tumor treating fields (TTFields) to the existing standard of care of radiochemotherapy. An understanding of the predicted long‐term prognosis for GBM patients is important to facilitate good clinical, personal and policy decision‐making, as survival at 5 years continues to improve. OBJECTIVE: To estimate the mean lifetime survival benefit for GBM patients of adding TTFields to the existing standard of care. METHODS: Standard regression‐based parametric extrapolations of overall survival were constructed and were fit to the EF‐14 trial data. These models underestimated the reported long‐term GBM survival rates. Parametric models assume a constant hazard function, which was not observed in the EF‐14 trial or epidemiological data, resulting in the underestimation. Survival was instead modelled using a previously described method that synthesized EF‐14 trial data with GBM epidemiological data and general population survival rates. RESULTS: The estimated mean lifetime survival from initiation of adjuvant treatment was 4.2 years with TTFields and 2.4 years without it, an increase of 1.8 years. The estimated incremental life years gained (LYG) was 1.3 years when a 3% discount rate was applied to future survival benefits. TTFields‐treated survivors who survived to 2 years were estimated to have a 20.7% chance of surviving to 10 years. CONCLUSIONS: The analysis indicated that treating GBM patients with TTFields substantially increased mean lifetime survival, consistent with the clinical findings of the EF‐14 trial. Current GBM treatment strategies offer improved prognoses compared to past therapies, and should be considered by physicians, patients and payers in GBM treatment decisions.