Lapatinib and trastuzumab were purchased from LC Laboratories and Mckesson Specialty Health, respectively. Stocks of L and T were prepared as described previously (10 (link), 19 (link)). Afatinib (Afa) and neratinib (Nrb) were purchased from LC Laboratories and Selleck Chemicals, respectively. Stocks of Afa and Nrb were prepared with DMSO.