A case of predominant solid adenocarcinoma with the L858R mutation. A DNA sequencing of EGFR showing normal (upper panel) and L858R mutant (lower panel). The position of the mutation is boxed. 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 L858R-specific antibody showing strong positivity (original magnification x200). C Immunohistochemical staining with E746-A750 del-specific antibody showing complete negativity (original magnification x200).