Tumor treating fields (TTFs) are an evolving new anticancer modality. The U.S. 
Food and Drug Administration has approved the first device, the NovoTTF-100A™, 
that uses this technology and is indicated for use in progressive glioblastoma 
multiforme after standard therapies have failed. Promising clinical trial 
results will likely lead to expanded uses in primary brain tumors and other 
cancer types. This article will review the concept of TTFs and their mechanism 
of action, and overview the TTF device and its approved usage.