Tumor treating fields (TTFields) use alternating waves in roughly the AM radio range to disrupt malignant cell division, shrinking tumors and helping to keep metastases in check. Devices to deliver the therapy currently are available from a single company-Novocure-but a number of clinical trials are underway globally with an eye toward expanding their use. When TTFields were discovered in 2000, researchers suspected that their primary mechanism of action involved physically interfering with mitosis as a cancer cell begins to divide. Healthy cells are not affected by the fields because they have different division rates than malignant cells and different physical and electrical properties. Research has revealed that the fields not only disrupt cancer cell division, but also interfere with DNA damage repair and a malignant cell's ability to move around the body, or metastasize. Studies show that TTFields can trigger cellular stress and chromosomal abnormalities that make it easier for the body's immune system to kill malignant cells.