PGR and breast cancer: As the most frequently diagnosed cancer in women worldwide, in 2018, breast cancer accounted for ~2.08 million diagnoses and resulted in over 626,000 deaths.1 In the United States, 41,760 women were expected to die from breast cancer in 2019, and diagnosis of 268,600 new cases was projected for the same year.2 Treatment options for breast cancer patients depend on the histological grade and expression status of the oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2/neu).