Comparison of enzyme immunoassay and immunohistochemical measurements of estrogen and progesterone receptors in breast cancer patients

Before replacing enzyme immunoassay of estrogen and progesterone receptors by immunohistochemistry, results of both methods were compared on 437 sampl es obtained from breast cancer patients (342 primary breast carcinomas, 16 local recurrences, 49 biopsies, and 30 tumor specimens obtained after neoad juvant treatment). Immunohistochemistry (IHC) results were first assessed s emiquantitatively on the basis of the estimated proportion of positive tumo r cells. and then quantitatively using the "quick score." Semiquantitative IHC hormone receptors results (positive greater than or equal to 10%) corre lated well with enzyme immunoassay status (positive > 15 fmol/mg protein) i n 358 surgical samples (342 primary tumors and 16 recurrences), with overal l concordance rates of 89.9% and 82.1%, respectively. Among the 100 discord ant cases, a large intraductal carcinoma component was observed in 7 of 36 cases for estrogen receptor (ER) and 15 of 64 for progesterone receptor (PR ). Thirty-five discordant cases also were observed near the cut-off values. Hormone receptor levels by enzyme immunoassay correlated strongly with the quantitative IHC "quick score." Whatever the method, hormone receptor stat us was associated with histologic grade (SBR) and tumor size, whereas age c orrelated strongly with ER positivity. Similar results were obtained for bi opsy specimens and posttreatment samples. This comparison improved the reli ability of the IHC technique. which is currently routinely used for ER and PR determination in the authors' institution.