Human SkBr3 (HTB‐30) and BT474 (HTB‐20) breast cancer cell lines were obtained from the American Type Culture Collection (ATCC). Lapatinib‐resistant (LR) clones were generated from long‐term treatment with Lapatinib (GlaxoSmithKline).24 (link), 25 (link) All cell lines were cultured in Dulbecco's modified Eagle medium/F12 (SH30004.04, HyClone) supplemented with 10% fetal bovine serum (10437‐028, Gibco), 1% penicillin‐streptomycin (SH40003.01, HyClone) at 37°C in an humidified atmosphere of 95% air and 5% CO2. LR clones were maintained in the presence of 1 μmol/L Lapatinib.