A simplified immuno-enzymetric assay of the epidermal growth factor receptor in breast tumors: Evaluation in 282 cases

The epidermal growth factor receptor (EGF-R) is currently being investigated in human clinical oncology, and particularly in breast cancer, as a potential prognostic factor and a biological target for therapy. As an alternative to the ¹²⁵I-EGF binding assay, we propose a sensitive immuno-enzymetric assay (IEMA) suitable for EGF-R assay in breast cancer. The assay is performed on solubilized extracts of the 105,000 g pellet of a tumor homogenate, allowing estrogen (ER) and progesterone (PR) assays to be made on the cytosol. The IEMA is performed on 96-well plates coated with the monoclonal anti-EGF-R antibody RI, through an anti-mouse IgG_2b bridge. Trapped EGF-R in the samples is covered by a second monoclonal antibody (MAb), 528, and revealed by an antilgG_2a-peroxidase complex. The sensitivity is I fmol/mg membrane protein, and the assay can be performed on tissue samples down to 50 mg. Two hundred and twenty primary ductal breast carcinomas assayed by this method showed a log normal distribution with a modal value of 8 fmol/mg prot., a mean at 18 and a median at 13 fmol/mg prot. EGF-R-rich tumors (>20 fmol/mg prot.) were highly correlated with the absence of estrogen receptors and/or with a high histological grade (SBR III). Our data demonstrate the validity of the IEMA assay of EGF-R in human breast tumors.