Efficacy of Extended Adjuvant Temozolomide Cycle Duration in Newly Diagnosed Glioblastoma: Four-year experience of a single major tertiary care institution

Objective: The primary aim of this study was to examine the benefit of extending adjuvant temozolomide (TMZ) duration beyond six cycles in newly diagnosed glioblastoma (GBM) measured by progression free survival (PFS) and overall survival (OS). Background: Standard post-surgical GBM treatment, per the Stupp protocol, dictates six-weeks of TMZ chemoradiation followed by six cycles of adjuvant TMZ. Clinical practice often involves extending adjuvant TMZ duration beyond six cycles at the discretion of the clinician in the absence of tumoral progression. Previous analysis has shown that extended adjuvant TMZ improves PFS but not OS outcomes, however, there is a paucity of research and consensus on clinical practice regarding this topic. Design/Methods: Data from 465 patients who underwent surgical intervention for GBM at a major tertiary care institution between July 2012 and September 2016 were analyzed. Only patients who underwent six-weeks of concurrent TMZ chemoradiation followed by at least six cycles (≥6) of adjuvant TMZ and were progression free 28-days after cycle-six were included. Data was compared between patients who underwent six cycles (=6) versus those who received more than six cycles (>6). PFS and OS were compared using a multivariate proportional hazard Cox model including age, sex, extent of surgery, number of adjuvant TMZ cycles, and molecular marker status (MGMT, EGFR, IDH1). Results: 167 newly diagnosed GBM patients who received both chemoradiation and adjuvant TMZ were included in final analysis. Of these, 60 patients received ≥6 cycles adjuvant TMZ and were progression free 28-days post cycle-six. Median OS for patients receiving =6 and >6 cycles was 22.47 and 25.76 months (p=0.61), respectively. Patients who received >6 cycles had a PFS hazard ratio, HR=0.80, (confidence interval, CI=(0.37–1.73), p=0.57); and an OS HR=1.62, (CI=(0.72–3.66), p=0.24). Conclusions: Extending adjuvant TMZ beyond six cycles was shown to not significantly impact either PFS or OS in newly diagnosed GBM patients. Disclosure: Dr. Barnett holds stock and/or stock options in Monteris Medical Inc. which sponsored research in which Dr. Barnett was involved as an investigator. Dr. Barnett holds stock and/or stock options in Monteris Medical Inc. Dr. Knusel has nothing to disclose. Dr. Ali has nothing to disclose. Dr. Saeed Bamashmos has nothing to disclose. Dr. Sagar has nothing to disclose. Dr. Ahluwalia has nothing to disclose.