Radioimmunohistochemistry of epidermal growth factor receptor in breast cancer

CONTEXT: Conflicting reports of epidermal growth factor receptor (EGFR) expression in breast cancer and inconstant relationships with established prognostic indicators and outcomes suggest difficulties with EGFR measurement. OBJECTIVE: To compare EGFR measurement in a panel of cell lines and in breast carcinomas by radioimmunohistochemistry (R-IHC), conventional immunohistochemistry (IHC), and a ligand binding (LB) assay. DESIGN: Eight EGFR-expressing cell lines and 50 primary breast carcinoma specimens were analyzed for EGFR by IHC, R-IHC, and LB assays. A further 153 primary breast cancer specimens were analyzed by R-IHC alone. RESULTS: All 3 assays were in good agreement for the cell lines. In the subset of the 50 carcinoma specimens, EGFR was detected by LB assays in 19 (38%) and by IHC in 24 (48%). However, R-IHC detected EGFR in 46 (92%) of 50 and in 186 (92%) of all 203 carcinoma specimens. The LB assay agreed poorly with R-IHC of carcinomas, possibly because the LB assay is sensitive to EGFR-expressing nontumor breast parenchyma in the tissue analyzed. Both IHC and R-IHC on carcinoma specimens agreed better, but 26 carcinoma specimens (52%) in which EGFR was not detectable by IHC had a 10-fold range in receptor level detectable by R-IHC. CONCLUSION: To elucidate the role of EGFR or other growth factor receptors in breast cancer requires accurate, sensitive receptor assays. With its dynamic range, R-IHC returned meaningful results over the entire range of expression actually present in breast cancer, which LB assays and IHC failed to do.