PGR and breast cancer: In the breast cancer chapter, levels of estrogen receptor (ER) and progesterone receptor (PR) expression, human epidermal growth factor receptor 2 (HER2) or erythroblastic oncogene B (ERBB2) expression, histologic grade, regional lymph node involvement, distant metastases, and prognostic biomarkers are included in order to confer precise prognosis and guide treatment decisions (14, 16).