To confirm the role of Brca1 loss in regulating Pdgfrβ in mammary epithelial and carcinoma cells, and to rule out the effect of stromal Pdgfrβ regulated by Brca1 loss in mammary tumorigenesis, we generated Brca1MGKO(Brca1f/f;MMTV-Cre or Brca1f/−;MMTV-Cre), p18−/−;Brca1MGKO, and p16−/−;Brca1MGKO mice in the Balb/c-B6 mixed background in which Brca1 was specifically deleted in mammary epithelia. The gene discussed is CDKN2A; the disease is carcinoma.