PGR and breast cancer: Globally, one million women are diagnosed with breast cancer, and approximately 150,000 (10-15%) have triple-negative breast cancers (TNBC; estrogen receptor (ER) 0-2, progesterone receptor (PR) 0-2, human epidermal growth factor receptor 2 (HER2) 0-2) with 7,500 new cases of TNBC per year in England alone. TNBC has a poorer prognosis, with a higher number of women relapsing and a shorter life expectancy.