Sensitivity to erlotinib in cell lines. Sensitivity to EGFR tyrosine kinase inhibitors was determined by treating cells with 1 μM erlotinib for 72 hours under serum-starved conditions. Apoptosis was assessed by integration of the sub-G1 peak and compared to cells treated with equal volume of vehicle (DMSO). Experiments were repeated in triplicate with error bars representing standard deviation. : denotes statistical significance (p < 0.05, two sided t-test for unequal variances).