Sanger cycle sequencing for EGFR mutation analysis. Sanger cycle sequencing for EGFR exons 18-21 was performed on DNA obtained with the new extraction method (H-PQ, see Methods for details). A: Electrophoretograms showing a 15-bp deletion in exon 19 (c.2236_ 2250del15, p.Glu764_Ala750del) of the EGFR gene. Arrows marked the starting and ending positions of the deletion. B: A heterozygous silent mutation in exon 20 (c.2361G > A, p.Q787Q).