Figure 2. Alteration of EGFR expression and EGFR mutation.

A. Expression of EGFR protein: in normal esophageal epithelium (a); negative, no discernible staining or background type staining (b); 1+, definite cytoplasmic staining and/or equivocal discontinuous membrane staining (c); 2+, unequivocal membrane staining with moderate intensity (d); and 3+, strong and complete plasma membrane staining (e). B. EGFR mutation: mutated EGFR (a-b); wild-type EGFR (c).