ESR1 and breast cancer: Our results indicate that most cells were viable after transfection with siRNA A. E-Syt1 knockdown significantly enhanced PI staining in MCF7, MDA-MB-231 and BT20 cells (Figure 4; p < 0.001); while PI staining of non-tumoral MCF10A and ER+ breast cancer T47D cells was unaffected by transfection of siRNA E-Syt1 (Figure 4).