RTHP-37. RATES AND IMPACT OF COMPLIANCE WITH TUMOR TREATING FIELDS THERAPY IN A GLIOMA COHORT

Tumor-treating fields (TTF) was approved in 2011 for recurrent glioblastomas then for adjuvant therapy in 2016 given the significant survival benefit shown in recent trials. Since 12/2012, 46 patients were treated with TTF for recurrent or newly diagnosed gliomas at Columbia University. We detail demographics, compliance rates and outcomes in this retrospective cohort. Of 42 treated patients with available compliance data, 16 (38%) were women and 2 (4.8%), 4 (9.5%) and 36 (85.7%) had WHO grade II, III and IV gliomas, respectively. Median age at diagnosis was 56 (23-84) years. TTF was used at recurrence in 33 (79%), with a median of 2 (0-4) prior recurrences, while 9 (21%) were treated at diagnosis. Prior therapies included bevacizumab (18, 43%), surgery [25 (60%) gross total], radiation and temozolomide. Median time to TTF initiation was 15 months, ranging 2.8 months to 17 years, from diagnosis. Median weighted compliance rate was 63% (6-89.4%). Patients were treated a median of 1.8 months, ranging 0.1 to 20.3 months. Concurrent systemic therapy was used in 34 (81%), including temozolomide (12, 29%), nitrosourea (2, 5%), bevacizumab (16, 38%), immunotherapy (23, 55%) or other (6, 14%). Objective response based on RANO was noted in 25 (60%) with combination TTF and systemic therapy. Only 2 (5%) experienced skin toxicity requiring interruptions. Progression free survival was 4.1 months, not significantly different among compliant (11, 26%) versus noncompliant users (median 4.4 vs. 4.1 months, p=0.3005), defined as the use of TTF for >75% of the time. The impact of compliance will be better assessed in multivariable analyses adjusted for potential confounders, especially for the glioblastoma subgroup. In randomized controlled trials, TTF therapy significantly increased survival for patients with glioblastomas. Highly variable and lower than advised compliance rates, however, may limit its benefit, despite the limited toxicities and safety of combination therapy.