An apparatus for inhibiting spreading of cancer cells in a target region, the apparatus comprising: an AC signal generator having (i) a first controllable output configured to apply an AC voltage across a first set of capacitively-coupled electrodes (41, 42) that are positioned in a vicinity of the target region, so as to impose an electric field in the target region in a first direction, and (ii) a second controllable output configured to apply an AC voltage across a second set of capacitively-coupled electrodes (43, 44) that are positioned in the vicinity of the target region, so as to impose an electric field in the target region in a second direction; and a controller configured to (a) control the first controllable output so that a first AC signal is generated for a first interval of time, the first AC signal having a first frequency and a first amplitude, wherein the first frequency and the first amplitude are selected to impose an electric field that disrupts mitosis of the cancer cells, (b) control the first controllable output so that a second AC signal is generated for a second interval of time, the second AC signal having a second frequency and a second amplitude, wherein the second frequency and the second amplitude are selected to impose an electric field that reduces motility of the cancer cells, and wherein the second amplitude is lower than the first amplitude, (c) control the second controllable output so that a third AC signal is generated for a third interval of time, the third AC signal having a third frequency and a third amplitude, wherein the third frequency and the third amplitude are selected to impose an electric field that disrupts mitosis of the cancer cells, (d) control the second controllable output so that a fourth AC signal is generated for a fourth interval of time, the fourth AC signal having a fourth frequency and a fourth amplitude, wherein the fourth frequency and the fourth amplitude are selected to impose an electric field that reduces motility of the cancer cells, and wherein the fourth amplitude is lower than the third amplitude, and (e) continuously repeat (a) through (d) in an alternating sequence during a course of treatment. an AC signal generator having (i) a first controllable output configured to apply an AC voltage across a first set of capacitively-coupled electrodes (41, 42) that are positioned in a vicinity of the target region, so as to impose an electric field in the target region in a first direction, and (ii) a second controllable output configured to apply an AC voltage across a second set of capacitively-coupled electrodes (43, 44) that are positioned in the vicinity of the target region, so as to impose an electric field in the target region in a second direction; and a controller configured to (a) control the first controllable output so that a first AC signal is generated for a first interval of time, the first AC signal having a first frequency and a first amplitude, wherein the first frequency and the first amplitude are selected to impose an electric field that disrupts mitosis of the cancer cells, (b) control the first controllable output so that a second AC signal is generated for a second interval of time, the second AC signal having a second frequency and a second amplitude, wherein the second frequency and the second amplitude are selected to impose an electric field that reduces motility of the cancer cells, and wherein the second amplitude is lower than the first amplitude, (c) control the second controllable output so that a third AC signal is generated for a third interval of time, the third AC signal having a third frequency and a third amplitude, wherein the third frequency and the third amplitude are selected to impose an electric field that disrupts mitosis of the cancer cells, (d) control the second controllable output so that a fourth AC signal is generated for a fourth interval of time, the fourth AC signal having a fourth frequency and a fourth amplitude, wherein the fourth frequency and the fourth amplitude are selected to impose an electric field that reduces motility of the cancer cells, and wherein the fourth amplitude is lower than the third amplitude, and (e) continuously repeat (a) through (d) in an alternating sequence during a course of treatment.