BRCA1 and breast cancer: We previously demonstrated that in mice loss of p18Ink4c (p18), an INK4 family cell cycle inhibitor, promotes MEC proliferation and induces Gata3 and Brca1-proficient luminal type mammary tumors, whereas depletion of either Brca1 or Gata3 on top of p18 null background leads to the development of BLBCs with activation of EMT [12, 25, 31, 32, 35].