Abstract
Abstract BACKGROUND Almost all GBM patients experience recurrent disease, and median survival after recurrence is 6 months. A phase III trial conducted to test safety and efficacy of TTFields alone versus chemotherapy (including bevacizumab) in recurrent GBM showed improved PFS at six months and one-year survival was 20% in both treatment arms. Stereotactic radiosurgery (SRS), another treatment option recommended at recurrence, has limitations due to the invasive nature of glioblastoma. TTFields may decrease the tumor aggressiveness outside the target area potentially by multiple pathways, including immunogenic cell death and DNA repair inhibition sensitizing to radiation. We hypothesize that combined SRS and TTFields will be complementary, improving outcomes with minimal toxicity. METHODS In this open-label, phase II trial 40 participants with recurrence will be treated with SRS and TTFields, starting in 2020. Recurrence will be defined on FET-PET or MRI using RANO criteria. At least 6 months between the end of the first course of radiotherapy and SRS is mandatory with recurrent tumor visible on FET-PET and/or MRI, with the maximum diameter < 5 cm by either technique. SRS must be delivered within 7 days of TTFields start. A 5-day SRS regimen is allowed. TTFields should be interrupted only during SRS. The sample size of the study was calculated for the comparison of survival against a historical control. With 40 patients followed until death, there is at least an 80% ability to detect a 19% difference in one-year survival rate and 17% difference in ORR (p=0.05) compared to the EF-11 clinical trial. The one-year survival and ORR rate were seen in 20% and 14% of TTFields patients in the historical control. Overall survival will be stratified by volume, PET-based treatment, SVZ invasion, MGMT methylation status, time to first progression, and TTFields compliance. Estimated study primary completion date is July 2023.
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