Quantitative determination of the epidermal growth factor receptor in cervical cancer and normal cervical epithelium by 2-color flow cytometry: evidence for down-regulation in cervical cancer.

Expression of epidermal growth factor receptor (EGFR) was quantified by 2-color flow cytometry in cervical cancer (n = 73) and normal cervical epithelium (n = 11). EGFR was determined using a murine monoclonal EGFR antibody, and number of bound antibodies was quantified adding calibration beads with defined antigenic binding sites. Tumor cells were identified by simultaneous DNA staining. Epithelium of normal cervical tissue was detected by labeling for cytokeratin. Results were compared with EGFR quantification by autoradiography on cryostat sections using a radioligand binding assay. A high degree of correlation was found between the 2 methods. In cervical carcinomas 14,600 binding sites/cell (median; range, 160-283,000 binding sites/cell) were detected, considerably less compared with normal cervical squamous epithelium, which was 30,700 binding sites/cell (median; range, 19,900-44,000 binding sites/cell). This finding clearly contrasts with other reports of enhanced EGFR expression in cervical cancer. The discrepancy may be explained by contamination of tissue homogenates used for radioligand or enzyme immunosorbent assays by non-epithelial tissue elements with low or absent EGFR expression. Interference with quantitative EGFR determination in epithelial cells may result in false low estimates of EGFR expression predominantly in normal cervical tissue. This should be avoided by identifying tumor and normal epithelial cells prior to analysis. In our study, 63% of cervical cancers expressed low levels of EGFR compared with normal cervical epithelium, and only 10% showed overexpression. There is evidence that cervical carcinomas overexpressing EGFR represent a small, but biologically distinct group of cervical cancers exhibiting enhanced aggressiveness associated with poor survival of the patients.