An apparatus for inhibiting spreading of cancer cells in a target region, wherein the apparatus comprises an AC signal generator and a controller which are configured to: (a) impose a first AC electric field in the target region for a first interval of time, wherein the first AC electric field has a first frequency and a first amplitude, and the first frequency and the first amplitude are selected so that the first AC electric field disrupts mitosis of the cancer cells； (b) impose a second AC electric field in the target region for a second interval of time, wherein the second AC electric field has a second frequency and a second amplitude, and the second frequency and the second amplitude are selected so that the second AC electric field reduces motility of the cancer cells, with the second amplitude being lower than the first amplitude； and (c) continuously repeat (a) and (b) in an alternating sequence during a course of treatment.
