Patients with ER+/PR− breast tumors as defined by gene expression profiling rather than by clinical assay alone tend to have poorer prognosis. Kaplan-Meier analysis of breast cancer patients stratified by ER+/PR+, ER+/PR−, and ER−PR−, where the status was determined by either clinical assay (left panels) or gene classifer (right panels). Profile datasets from Wang (A), Miller (B), and van de Vijver (both all tumors (C), and the subset of tumors that did not receive either hormone therapy or chemotherapy (D), are considered). Log-rank statistic p-values evaluate whether there are significant differences in time to poor outcome event between any of the three groups. For Wang and van de Vijver datasets, measured outcome is distant-metastasis-free survival; for Miller dataset, outcome is disease-specific survival. N, number of patients.