GATA3 and breast cancer: We then determined the expression of GATA3 in human breast cancer cell lines and found that GATA3 mRNA and protein levels were high in BRCA1 proficient cells (T47D and MCF7) and low or undetectable in BRCA1 deficient (BT20, MDA-MB231, SUM149, and HCC1937) cells (Figure 1C-D).