High sensitivity and specificity of immunohistochemistry for the detectionof hormone receptors in breast carcinoma: comparison with biochemical determination in a prospective study of 793 cases

Aims: The hormone receptor (HR) status of breast cancer is an important pro gnostic factor and predictive parameter of the response to hormone therapy. Enzyme immunoassay (EIA) is currently the standard for determination of HR , but immunohistochemistry (IHC) represents a potentially useful alternativ e. We used IHC to determine HR status in a large prospective study and comp ared the results to those obtained by ETA, This study was designed to deter mine which technique should be used in daily practice in our institution wh ich manages a large number of patients. Methods and results: Oestrogen (ER) and progesterone (PgR) receptor status was evaluated in a prospective series of 793 infiltrating breast cancers by IHC in paraffin-embedded tissue sections, using antibodies 6F11 and 1A6, w ith a rigorous quality control of the methodology. ER were found to be sign ificantly expressed in 81% of cases after IHC analysis and in 78% of cases by EIA. For PgR, the respective rates of positivity were 65% and 69%. The t umour BR level detected by either technique was significantly correlated wi th the value of tumour size, histological grade and S-phase fraction. A sig nificant link was observed between the percentage of labelled cells after I I-IC analysis and the amount of protein detected by EIA. Critical analysis of discordance found that, in the group of invasive lobular carcinomas, the rate of IIR positivity was higher with IHC (84%) than with EIA (45%) and t hat, in the overall population, IHC was more specific than EIA, since cases with nonrelevant positivity related to intraductal normal or neoplastic ce lls expressing Im could be discarded, The cost of IHC analysis was found to be about one-third of that of EIA, Conclusions: IHC is more sensitive, specific and economical than EIA. It sh ould constitute the new standard technique provided that good quality assur ance procedures are respected.