Patients were first stratified into ER-positive and ER-negative groups and then for each group a classifier was trained using age, tumor stage, tumor grade, ER status, PR status, HER2 status, and lymph node metastasis status as features, in addition to scores from the E2F4, MammaPrint, or Oncotype DX signatures, depending on the comparison being made. The gene discussed is ESR1; the disease is neoplasm.