Abstract
The epidermal growth factor receptor (EGFโR) 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^IโEGF binding assay, we propose a sensitive immunoโenzymetric assay (IEMA) suitable for EGFโR 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 96โwell plates coated with the monoclonal antiโEGFโR antibody RI, through an antiโmouse IgG~2b~ bridge. Trapped EGFโR in the samples is covered by a second monoclonal antibody (MAb), 528, and revealed by an antilgG~2a~โperoxidase 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. EGFโRโrich 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 EGFโR in human breast tumors.