ESR1 and breast cancer: Direct treatment of MCF-7 (ER+, low metastatic), MDA-MB-231 and Hs578T (ER-, highly metastatic) breast cancer cells with mild (0.5 kHz/27.6 kV) or strong (1.5 kHz/27.6 kV or 0.5 kHz/31.2 kV) DBD-CAP conditions revealed a time- and dose-dependent effect on cell viability.