EGFR and lung cancer: Pemetrexed-resistant lung cancer cell lines were obtained by culturing PC9 [EGFR exon 19 deletion (delE746-A750)] and H1993 [EGFR wild-type] cells with stepwise increases in the pemetrexed concentration for over six months; the pemetrexed-resistant sublines were designated as PC9-MTA and H1993-MTA, respectively.