ESR1 and breast cancer: While in the past many laboratories have contributed to identify ER interacting proteins using a variety of experimental approaches and cell lines (a detailed list can be accessed at IntAct database: http://www.ebi.ac.uk/intact/query/estrogen%20receptor%20alpha?conversationContext=1), the recent advance of high resolution mass spectrometry (MS) has allowed for a more comprehensive analysis of breast cancer proteomes and interactomes [19-21] including the ERα interactome [17, 22-26].