INNV-07. Effects of Temozolomide Dose Rounding on Outcome in Glioblastoma

Abstract BACKGROUND Temozolomide (TMZ) with concomitant radiation is the standard therapy for treating glioblastomas (GBM) and is dosed based on body surface area (BSA) using a goal dose of 75 mg/m2. Neurooncologists have different methods of dosing patients, with some dosing within 5mg of the calculated dose and others rounding to reduce patient burden. We aimed to determine the effect of rounded doses of TMZ on survival. METHODS We conducted a single-center retrospective review of 380 patients with GBM from 2013 to 2024. Relevant patient data was extracted from electronic medical records. Kaplan-Meier curves and Cox regression models were used to determine survival outcomes. RESULTS No significant impact on survival outcomes was observed when distance from the calculated temozolomide dose was analyzed as a continuous variable (p = 0.309) adjusting for MGMT, the extent of resection, the number of radiation fractions, and performance status. Even limited to just MGMT methylated tumors, TMZ dose did not affect survival. When compared to people with dose within 5mg of 75mg/m2, survival was not changed with doses of 5-20 mg below the calculated dose (HR 0.842, p= 0.226). BMI had no impact on survival outcomes. Multivariable analysis revealed that patients with MGMT methylated tumors, total resection, higher Karnofsky performance scores, and ≥ 30 radiation fractions had improved survival (p < 0.01). Dose interruptions were not significantly more likely with doses above 75 mg/m2 (14%) than with doses at or below 75 mg/m2 (9%) (p = 0.22). CONCLUSION Rounding temozolomide doses does not significantly impact survival outcomes or risk of treatment interruptions for patients with GBM. These findings may allow neuro-oncologists to prioritize reducing pill burden and treatment costs without compromising patient outcomes. Clinical trials should consider dropping requirements for temozolomide dose within 5mg of 75mg/m2.