Figure 3. Screening for resistance alleles.

A. Selection of PC9 cells in media containing increasing concentrations of erlotinib resulted in the PC9-ER line, which is unaffected by doses of erlotinib up to 1 µM. B. The IL3-independent Ba/F3 clone 1C8 recovered by cDNA library screening of PC9-ER cells contains both the Δex19 activating mutation and the T790M mutation in EGFR. C. Sanger sequencing shows that only a small fraction of EGFR amplified from PC9-ER cells harbors the T790M alteration, in contrast with 1C8.