ESR1 and breast cancer: Treatment of MCF-7 and T47D cells with E2 increased VEGF mRNA expression, but E2 stimulation did not shown apparent effect on VEGF expression in MDA-MB-231 cells (Figure 4A), thus suggesting that E2 stimulation influences VEGF expression only in ER-α positive breast cancer cells but not in MDA-MB-231 cells that lack ER-α expression.