library_construction_protocol: MCF7 xenografts treated with hormone pellets were dissociated to single cells, mouse cells were depleted with immunomagnetic beads (Miltenyi, cat#130-104-694). RNA extracted using TriZOL reagent (Invitrogen) total RNA was isolated with miRNeasy Mini Kit (Qiagen). Illumina HiSeq, 2x150bp configuration