Male C57BL/6 (8–9 weeks old) mice were purchased from Vital River (Beijing, China). The human breast cell lines (BCap37, Hs 578T, MDA-MB-231, MDA-MB-468, BT-474, SK-BR-3, MCF-7, Hs 578Bst and HBL-100) were purchased from the cell bank of the Chinese Scientific Academy. BCap37, BT-474 and MCF-7 cells were cultured in Roswell Park Memorial Institute 1640 medium (Gibco, 31800105, Carlsbad, CA, USA) with 10% fetal bovine serum (FBS; Biological Industries, 04-0101-1, Cromwell, CT, USA). MDA-MB-231 and MDA-MB-468 cells were cultured in Leibovitz's L-15 medium (Gibco, 11415114) with 10% FBS. Hs 578T cells were cultured in Dulbecco's modified Eagle's medium (DMEM; Gibco, 12430047) supplemented with 0.01 mg/ml bovine insulin (Solarbio, I8040, Beijing, China) and 10% FBS. SK-BR-3 cells were cultured in McCoy's 5A medium (modified, Gibco, 16600082) with 10% FBS. Hs 578Bst cells were cultured in DMEM with 50 ng/ml epidermal growth factor (Gibco, PHG0311) and 15% FBS. HBL-100 cells were cultured in DMEM with 10% FBS. The cell culture medium was changed every 2–3 days, and the cells were passaged with 0.25% trypsin-EDTA (Gibco, 25200056) and grown to 90% confluence. The cultures were kept at 37 °C with 5% CO2 in a water-jacketed incubator (Thermo Scientific, Waltham, MA, USA).