ESR1 and breast cancer: Luciferase reporter gene assays showed that overexpression of BCAS2 is able to enhance ERα transcriptional activity to an extent similar or greater than that found for the SRC-1 coactivator in ER positive (MCF7) (Figure 2A) or ER negative (MDA-MB-231) breast cancer cell lines in the presence of E2 (Figure 2B).