MED1 and breast cancer: Of the other Mediator subunits, MED1 is required for ER-mediated gene transcription and BC cell growth37 and has also been implicated in vascular invasion.13 On the other hand, recurrent MED12 somatic mutations have been seen in fibroadenomas and phyllodes tumours.38 In contrast, the functional relationships of MED7 are little known.