EVALUATION OF A DISPLACEMENT ASSAY WITH TAMOXIFEN AS PROGNOSTIC INDICATOR IN BREAST-CANCER PATIENTS WITH ESTROGEN-RECEPTOR-POSITIVE TUMORS

A displacement assay with tamoxifen, based on the relative binding aff inity of tamoxifen and estradiol for the estrogen receptor (ER), was p roposed in 1990 as prognostic indicator for breast-cancer patients. Va lidation of its predictive results in relation to the outcome of 73 pa tients with ER+ tumors is analyzed. ER, progesterone receptor (PgR) de terminations and other conventional prognostic factors in relation to the displacement assay, were considered. Displacement assay results al lowed ER+ tumors to be grouped as displaceable (D) or weakly displacea ble (WD), with the implication that D tumors should respond better to tamoxifen (Tam) administration, Survival and disease-free interval cur ves showed highly significant differences between patients with ER+ D and ER+ WD tumors, For survival, including all tumor stages, 73.9% of patients were alive at 9 years after surgery in the group with D tumor s and 37.0% in the group with WD tumors (p < 0.005); relative contribu tion of the different stages is analyzed. Addition of axillary-node nu mber increased the prognostic significance of displacement categories for survival and disease-free interval. PgR determination as another E R functional expression failed to show significant differences for sur vival and disease-free interval between ER+ PgR(+) and ER+ PgR(-) tumo rs. Thus, results from the displacement assay and from PgR determinati ons reflect 2 independent ER functional expressions. Displacement assa y data appear as reliable prognostic indicators of breast-cancer outco me, and contribute to more appropriate treatment decisions in this pat hology. (C) 1997 Wiley-Liss, lnc.