Methods for treating tumors employing HSp90 inhibitors in combination with nanosecond pulsed electric fields (nsPEFs) are disclosed. The methods are directed to induce regulated cell death (RCD) in tumor cells and tissues. Further, Hsp90 inhibitors in combination with nsPEF are used at low non-toxic concentrations, thereby reducing the side-effects associated with these drugs. Additionally, nsPEFs are employed at lower electric fields and/or with fewer number of pulses than when nsPEFs are employed alone. Further, the mechanisms by which nsPEFs and Hsp90 inhibitors act upon cancer cells are different, thereby combining these treatments results in a synergistic effect.
