EGFR and lung adenocarcinoma: We next tested H1975, a human lung adenocarcinoma cell line with both an exon 20 T790M gatekeeper mutation and an exon 21 L858R mutation in EGFR; and PC-9/KGR1, a cell line with both an exon 20 T790M gatekeeper mutation and deletions of EGFR exon 19.