MMTV-Neu/P53KO (ER−) mouse mammary cancer model

MMTV-Neu^+/−/p53 KO^+/− mice were generated and maintained as previously described (23). MMTV-Neu transgenic mice [strain FVB/N-Tg (MMTV-Neu) 202 Mul/J] were purchased from the Jackson Laboratory (Bar Harbor, ME, USA). A p53 deficient line (p53 NS-T) was purchased on a C57BL background (Taconic) and back-crossed at least 5 times onto a FBV/N background. For generation of MMTV-Neu^+/−/p53 KO^+/− females, p53^−/− males were crossed with MMTV-Neu^+/+ females. MMTV-Neu females were generated by crossing MMTV-Neu^+/+ males with FVB/NJ females. The animal rooms were lighted 12 h/day in a facility specially designed for administering chemical carcinogens to animals. Mice were given diet (Teklad 4% mash) and water ad libitum. Mice were treated with gefitinib by gavage either daily (5 times/week) or weekly beginning at 6 weeks of age. Mice were examined weekly for the development of palpable mammary tumors beginning at 4 months of age. Mice were sacrificed when a large palpable mammary tumor developed or at termination when mice were 11 months of age.