ESR1 and breast cancer: Based on ERα ChIP-chip data and microarray mRNA expression profiles after E2 stimulation of MCF7 breast cancer cells, we categorized ERα regulatory mechanisms into three groups (additional file 2): genomic action with ERα direct ERE binding (DBGA), genomic action with ERα indirect/ERE-independent (e.g., AP-1) binding (I-DBGA), and non-genomic/ligand-independent action (NGA).