P14.71 Tumor Treating Fields combined with radiotherapy and temozolomide for newly diagnosed glioblastoma: final safety and efficacy results from a pilot study

Abstract BACKGROUND Tumor Treating Fields (TTFields) are a non-invasive, loco-regional, anti-mitotic treatment consisting of low intensity alternating electric fields. The combination of TTFields with maintenance temozolomide significantly improved survival versus temozolomide alone in the phase 3 EF-14 study in newly diagnosed glioblastoma (ndGBM). In preclinical studies, TTFields increased the number of glioma cells undergoing cellular death following radiotherapy (RT) by inhibiting DNA damage repair, suggesting a radio-sensitizing effect of TTFields. This pilot study is the first to evaluate the safety and feasibility of administering TTFields concomitant to RT and TMZ in ndGBM patients. MATERIAL AND METHODS Patients diagnosed with ndGBM were treated with TTFields/RT/TMZ followed by maintenance TMZ and TTFields for up to 24 months. TTFields (200kHz) were delivered for >18 hours/day while the transducer arrays were removed during delivery of RT. TMZ was administered at a dose of 75 mg/m2/daily for 6 weeks and RT at a total dose of 60 Gy. The primary endpoint was safety of the combined TTFields/RT/TMZ; secondary endpoints included progression-free survival (PFS), overall survival (OS) and toxicity. Adverse events (AEs) were graded according to CTCAE V4.0. RESULTS 10 ndGBM patients that recovered from maximal debulking surgery or biopsy were enrolled at a single center in Israel between April and December 2017. Five patients (50%) had undergone gross total resection while the rest had biopsy only. Eight of the patients were male, median age was 59, median KPS was 80 and median dose of RT was 60 Gy. Six patients (60%) reported at least one AE. The most common AE was TTFields-related skin toxicity, reported in four patients (40%), all of which were grade 1–2 in severity. Two patients reported serious AEs (seizures and general deterioration) that were considered unrelated to TTFields. Median PFS with RT/TMZ/TTFields was 10.5 months. Median OS has not yet been reached. CONCLUSION The proportion of patients with TTFields-related skin toxicity was similar to that reported in ndGBM patients in the randomized Phase III study (52%), where patients started TTFields at least 4 weeks after RT. No other TTFields-related toxicities were reported and there were no increase in RT- or TMZ-related toxicities as a result of combining TTFields with RT in addition to TMZ. Based on the safety and preliminary efficacy results of this pilot study, a phase II randomized study has been initiated to investigate the efficacy of concomitant RT/TMZ/TTFields in 60 ndGBM patients.