ESR1 and breast cancer: We found that PEDF protein (Figure 1a) and mRNA (Figure 1b) levels were dramatically reduced in endocrine-resistant MCF-7:5C, MCF-7:2A, and BT474 breast cancer cells compared with endocrine-sensitive MCF-7, T47D, and ZR-75-1 cells with no PEDF observed in ER-negative MDA-MB-231 cells.