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 125 I‐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.