PURPOSE: The HER-2/neu protein (p185) has become a promising target for antibody therapy in breast cancer. We tested the feasibility of a quantitative approach for HER-2/neu testing based on the analysis of tumor tissue extracts by an enzyme-linked immunosorbent assay (ELISA). EXPERIMENTAL DESIGN: Tumor tissue extracts of primary human breast cancers (n=124) were prepared using a triton-based buffer. HER-2/neu concentration was quantified by ELISA. Paraffin-embedded tissue sections of the same tumors were analyzed by immunohistochemical staining applying the monoclonal HER-2/neu antibody TAB 250 (n=124) and by chromogenic in situ hybridization (CISH) (n=73). RESULTS: Concentrations of p185 in tissue extracts determined by ELISA varied from 1 to 927 ng per mg protein with a median of 25 ng/mg protein, whereas normal breast tissue showed values from 0.4 to 5.5 ng/mg with a median of 2.2 ng/mg (p
