A case of predominant acinar adenocarcinoma with the exon 19 deletion mutation (E746-A750 del). A DNA sequencing of EGFR showing normal (upper panel) and the E746-A750 del mutant (lower panel). The position of the mutation is indicated. The mutant sequence appears to be homozygous with complete absence of normal sequence. This is because of the use of a “clamp” strategy to suppress amplification of the normal sequence, as described in the methods section. B Immunohistochemical staining with E746-A750 del-specific antibody showing strong positivity (original magnification x200). C Immunohistochemical staining with L858R-specific antibody showing complete negativity (original magnification x200).