Patients with the L747_A750 > P mutation demonstrated significantly worse PFS, DOT and OS than those with the E746_A750 and L747_P753 > S mutations...This study shows differential clinical outcome to EGFR-directed therapy within EGFR ex19 del tumors, specifically that pts with ex19 del L747_A750 > P have inferior outcomes versus those with E746_A750 or L747_P753 > S when treated with erlotinib.