ESR1 and breast cancer: Of those, FOXA1, ESR1 and GATA3 are not only reported as co-expressed (Sachs et al., 2013) and co-localized (Kong et al., 2011) in breast cancer cells, but there is even strong evidence suggesting they might form an enhanceosome that regulates many genes involved in the ER signaling cascade (Kong et al., 2011).