PGR and breast cancer: Breast cancer is the most frequent malignant cancers which are diagnosed and it is also one of the main reasons for death worldwide.1, 14 In China, the occurrence rate of breast cancer has soared obviously in recent decades.15 Oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) are common breast cancer biomarkers and the classification of breast cancer is mainly based on them.