A method of detecting cancer cells is disclosed. The method comprises (a) contacting the cell with a substrate for an enzyme under conditions wherein the enzyme catalyzes a reaction of the cell with the substrate, so as to generate a product capable of producing an electrical signal; and (b) measuring a level of the electrical signal, wherein a difference in a level of the electrical signal compared to a predetermined threshold is indicative of a cancer cell. The method may be adapted for diagnosis, monitoring a cancer therapy, identifying agents capable of treating cancer and individually optimizing a cancer therapy.