Analyses of the level of expression of the epidermal growth factor receptor (EGF-R) of breast cancer tumors may add independent information about the prognosis of individual patients. Furthermore, the use of monoclonal antibodies directed against EGF-R as therapeutic tools (e.g., Mab 425) requires a reliable evaluation of the individual EGF-R content. Various analytical methods have been published, including (Scarff RW and Torloni H: World Health Organization, Geneva, 1968), biochemical detection of EGF-R by a radiolabeled physiologic ligand [I-125]EGF, (Early Breast Cancer Trialists' Collaborative Group: Lancet 329: 1-15, 1992) biochemical analyses of EGF-R content with a monoclonal antibody, and (McGuire WL and Clark GM: N Engl J Med 326: 1756-1761, 1992) immunohistochemical EGF-R detection. We measured the EGF-R content in membrane pellets derived from routine processing for evaluation of estrogen (ER, ER-EIA) and progesterone receptor (PgR; PgR-EIA) in 185 breast cancers and 18 benign breast samples, using a single-point saturation assay (RBA). Simultaneously, ER (ER-ICA), PgR (PgR-ICA), and EGF-R immunohistochemistry was performed on frozen sections of the same tumors. Various cell lines and normal skin tissue samples served as EGF-R positive or negative controls. The results of the two different EGF-R analyzing methods were compared with other biological characteristics of the tumors. 37% of the tumors were EGF-R positive. There was an inverse correlation between the ER or PgR and the EGF-R content. EGF-R overexpression correlated with high tumor grade. Analyses of EGF-R content in membrane pellets of breast cancer samples by single point saturation assay as well as the evaluation of tumor sections by immunohistochemistry can be performed routinely. The results obtained with both analytical methods did not differ significantly. but the immunohistochemistry proved to be more difficult to perform and to interpret. Thus, we prefer to perform both analytical methods simultaneously to provide information potentially useful for clinical management of individual cancer patients.

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