An apparatus for selectively destroying or inhibiting the growth of rapidly-dividing cells located within a target region (1500) of a patient, the apparatus comprising: a plurality of arrays of electrodes (A1-A9, N1-N9), wherein the electrodes (A1-A9, N1-N9) each have a surface configured for placing against the patient's body； and an AC voltage source electrically connectable to respective ones of the electrodes (A1-A9, N1-N9)； wherein the AC voltage source and the electrodes (A1-A9, N1-N9) are configured so that, when the electrodes (A1-A9, N1-N9) are placed against the patient's body, an AC electric field is imposed in the target region (1500) with an orientation that rotates with respect to the target region (1500), the electric field having frequency and field strength characteristics that cause the electric field to (a) selectively damage cells that are undergoing cell division and (b) leave cells that are not undergoing cell division substantially unharmed.
