Epidermal growth factor receptor assay: validation of a single point method and application to breast cancer

Epidermal growth factor (EGF) is a 6000 kDa peptide which exerts its biological effects by binding to a specific cell membrane receptor (EGF-R). Extensive studies on EGF-R in breast tumors have demonstrated the prognostic value of such assays. EGF-R measurement is also reportedly potentially useful in other tumors. Classically, the EGF-R content of tumor cell membrane preparations is evaluated by competition between a given concentration of labeled ligand and various concentrations of unlabeled ligand. The large quantity of tumor tissue required (approx. 0.5 g) is a serious limitation for wide-spread use of EGF-R assays. In order to validate a miniaturized EGF-R assay method, the principle of a single-dose technique (SD) using a single concentration of labeled ligand (1 nM) was investigated in the present work. Only 100-150 mg wet tissue were required for routine analysis by the SD method. The correlation between the SD method and Scatchard analysis calculated from 41 different breast carcinoma samples was very satisfactory (r = 0.973, p less than 0.001). Analysis of intra-assay and inter-assay reproducibility revealed a comparable EGF-R status in given samples. The correlation between EGF-R levels and steroid receptors was investigated in 105 individual breast tumors. EGF-R levels were inversely correlated with the estradiol receptor values. No correlation was found with progesterone receptors. The simplified SD method for EGF-R measurement appears suitable for large scale clinical studies aimed at investigating the potential utility of this biological tumor marker.