We used mouse TumorGraft TM models of untreated TNBC and PR+BC, as well as TNBC TumorGraft animals treated with Doxorubicin/ Cyclophosphamide/ Paclitaxel (TNBC/DCP) and PR+BC animals treated with Topotecan (PR+BC/TOP) or Crizotinib (PR+BC/CRIZ) to analyze the roles of miRNAs in tumor brain and chemo brain. This evidence concerns the gene PGR and breast cancer.