INTRODUCTION: Local control is fundamental, both for the curative as well as the 
palliative treatment of cancer. Tumor treating fields (TTFields) are low 
intensity (1 ? 2 V/cm), intermediate frequency (100 ? 200 kHz) alternating 
electric fields administered using insulated electrodes placed on the skin 
surrounding the region of a malignant tumor. TTFields were shown to destroy 
cells within the process of mitosis via apoptosis, thereby inhibiting tumor 
growth. TTFields have no effect on non-dividing cells.
AREAS COVERED: This article reviews in vitro and in vivo preclinical studies, 
demonstrating the activity of TTFields both as a monotherapy as well as in 
combination with several cytotoxic agents. Furthermore, it summarizes the 
clinical experience with TTFields, mainly in two indications: one in recurrent 
glioblastoma multiforme: in a large prospective randomized Phase III trial 
TTFields was compared with best standard care (including chemotherapy): TTFields 
significantly improved median overall survival (OS) compared with standard 
therapy (7.8 vs 6.1 months) for the patients treated per protocol. Importantly, 
quality of life was also better in the TTFields group. The second indication was 
a Phase II study in second-line non-small cell lung cancer, where TTFields was 
administered concomitantly with pemetrexed. This combination resulted in an 
excellent median OS of 13.8 months. Interestingly, the progression-free survival 
(PFS) within the area of the TTFields was 28, however, outside the TTFields the 
PFS was only 22 weeks.
EXPERT OPINION: The proof of concept of TTFields has been well demonstrated in 
the preclinical setting, and the clinical data seem promising in various tumor 
types. The side effects of TTFields were minimal and in general consisted of 
skin reaction to the electrodes. There are a number of ways in which TTFields 
could be further evaluated, for example, in combination with chemotherapy, as a 
maintenance treatment, or as a salvage therapy if radiotherapy or surgery is not 
possible. While more clinical data are clearly needed, TTFields is an emerging 
and promising novel treatment concept.