AbstractEstrogen receptor (ER) and progesterone receptor (PR) assays are used to guide the hormonal treatment of metastatic/recurrent carcinoma of the breast. Sensitivity, specificity, and predictive value were calculated in comparing no receptor testing, ER testing alone, PR testing alone, and ER and PR in parallel. Analyses demonstrate that the indications for utilizing receptor assays are influenced by the valuation of uncertain outcomes and whether hormonal therapy is routinely planned in the absence of receptor test information. The PR assay appears best suited when patient outcome values mandate minimizing the likelihood of a false-positive outcome, with a corresponding increase in the likelihood of a true-negative outcome, even if this results in a reduced chance of a true-positive outcome and an increased chance of a false-negative outcome. Test specificity gives PR an advantage in this case. The ER assay has a comparative advantage when there is little difference in value between true-negative and false-positive outcomes and the primary contribution of testing is to maximize true-positive outcomes, while correspondingly minimizing the false-negative outcomes. This requires high test sensitivity. In either case, parallel testing does not appear to add appreciably to single test performance.