Epidermal growth factor receptors in breast cancer: comparison of radioligand and immunocytochemical assays.

Epidermal growth factor receptors (EGFR) are part of second generation biological factors that clinicians caring for breast cancer patients wish to evaluate for their prognostic value. This aim requires the standardization of methods: the radioligand assay (RLA) for the quantification of EGF binding sites was performed on membrane pellets from 261 breast cancer samples (ligand binding and hydroxylapatite separation as recommended by the EORTC Receptor Study Group); the immunocytochemical assay (ICA) for the staining of EGFR antigenic sites was performed on fine needle aspiration (FNA) cytology or touch imprints from 97 surgical specimens. The percentage of EGFR positivity by RLA (specific binding higher than 1% of total radioactivity) and the EGFR positive rate by ICA (more than 5% of stained cells) were respectively 43% and 38%. For 61 cases assayed on the same patient both methods revealed a concordance of 85%. Our results show that both methods are complementary and give quantitative data and information on tumor heterogeneity when they are performed in parallel. The next step of this study will be to determine the prognostic value of EGFR in these subpopulations of tumors for the adjustment of adjuvant treatment.