ESR1 and breast cancer: To identify these potential ER regulators in an unbiased manner, we constructed a Bayesian gene regulatory network, as previously described [21], using ER+ breast cancer samples from the TCGA (n = 623), METABRIC (n = 1505), Miller (n = 213) and Wang (n = 209) datasets and transcription factor-target interactions from the ENCODE project [22] and MCF7 ChIP-chip data [23].