Lysates from 293T cells transiently transfected with cDNAs encoding either EGFR WT, T854A, L858R, or L858R plus T854A and treated with different concentrations of erlotinib were immunoblotted for phospho-EGFR (Y1092), total EGFR, and Actin. T854A reduced the degree of inhibition of phospho-EGFR by erlotinib relative to WT or L858R EGFR. Actin is shown as a loading control.