Glioblastoma multiforme (GBM) is the most common form of primary malignant brain 
cancer. Median overall survival (OS) for newly diagnosed patients is only about 
12 to 18 months. GBM tumors invariably recur, and there is no widely recognized 
and effective standard treatment for recurrent GBM. NovoTTF Therapy is a novel 
and US Food and Drug Administration (FDA)-approved antimitotic treatment for 
recurrent GBM with potential benefits compared with other options. Recurrent GBM 
patients from two prior trials with demonstrated radiologic tumor response to 
single-agent NovoTTF Therapy were analyzed to better characterize tumor response 
patterns and evaluate the associations between response, compliance, and OS. In 
addition, a compartmental tumor growth model was developed and evaluated for its 
ability to predict GBM response to tumor-treating fields (TTFields). The overall 
response rate across both trials was 15% (4% complete responses): 14% in the 
phase III trial (14/120) and 20% (2/10) in a pilot study. Tumor responses to 
NovoTTF Therapy developed slowly (median time to response, 5.2 months) but were 
durable (median duration, 12.9 months). Response duration was highly correlated 
with OS (r(2) = .92, P<.0001), and median OS for responders was 24.8 months. 
Seven of 16 responders exhibited initial tumor growth on magnetic resonance 
imaging. Compliance appeared to be linked with both improved response and 
survival. The tumor growth model predicted tumor arrest and shrinkage only after 
several weeks of continuous NovoTTF Therapy, consistent with the observed 
clinical findings of initial transient tumor growth in some patients. NovoTTF 
Therapy is a novel antimitotic treatment for recurrent GBM associated with 
slowly developing but durable tumor responses in approximately 15% of patients. 
Some responders exhibit initial tumor growth before shrinkage, indicating 
treatment should not be terminated prior to allowing for the full effect of 
NovoTTF Therapy to be realized. OS is longer in responders than in 
nonresponders. High daily compliance rates may be associated with increased 
likelihood of an objective response and are predictive of improved survival.