Analytical and clinical performance of progesterone receptor antibodies in breast cancer

Clones evaluated in this study had a high level of concordance with IHC despite PR (1E2) demonstrating higher analytical binding properties than other clones. In a minority of cases (1.3% for 1E2 and 2.5% for 636) IHC results could convert estrogen receptor (ER)−/PR− to ER−/PR+ tumors, making these patients potentially eligible for endocrine therapy.