Enhanced phosphorylation of the epidermal growth factor receptor at the site of tyrosine 992 in esophageal carcinomas.

This study aimed to determine whether epidermal growth factor receptor (EGFR), which has been reported to be frequently overexpressed in esophageal carcinoma cells, is actually activated in the cells. Paraffin-embedded specimens of 39 cases of esophageal carcinoma were analyzed immunohistochemically with anti-EGFR polyclonal antibody (alpha-EGFR Ab) and also an anti-phospho-EGFR-specific polyclonal antibody (alpha-p-EGFR(Tyr992) Ab) that specifically recognizes phosphorylated tyrosine 992 of EGFR. All of the 39 cases were found to express EGFR, but the expression levels were not significantly higher than those in basal cells of the normal esophageal epithelium. In 38 of the 39 cases, alpha-p-EGFR(Tyr992) immunoreactivity was evident. Interestingly, the positively stained carcinoma cells were not distributed diffusely, and strongly immunostained cells tended to be localized in areas of severe dysplasia and in microinvasive foci just adjacent to the main invasive carcinoma. However, the deeply invasive front never exhibited positive immunoreactivity. The present findings suggest that phosphorylation of EGFR( Tyr992) may play some specific functional role in esophageal carcinomas besides promotion of cell proliferation.