Novocure GmbH, Lucerne, Switzerland 1 article published in JoVE Cancer Research Determining the Optimal Inhibitory Frequency for Cancerous Cells Using Tumor Treating Fields (TTFields) Yaara Porat1, Moshe Giladi1, Rosa S. Schneiderman1, Roni Blat1, Anna Shteingauz1, Einav Zeevi1, Mijal Munster1, Tali Voloshin1, Noa Kaynan1, Orna Tal1, Eilon D. Kirson2, Uri Weinberg3, Yoram Palti2 1Preclinical Research Department, Novocure Ltd., Haifa, Israel, 2Novocure Ltd., Haifa, Israel, 3Novocure GmbH, Lucerne, Switzerland Tumor Treating Fields (TTFields) are an effective anti-tumor treatment modality delivered via the continuous, noninvasive application of low-intensity, intermediate-frequency, alternating electric fields. TTFields application to cell lines using a TTFields in vitro application system allows for the determination of the optimal frequency that leads to the highest reduction in cell counts.