PGR and breast cancer: As the most common female cancer, breast cancer is diagnosed in more than 266 120 patients in the United States each year.1 Although representing only about 10%‐20% of patients, triple‐negative breast cancer (TNBC) patients had much worse prognosis than other subtypes owing to an inherently aggressive clinical behavior and a lack of recognized molecular targets for therapy (ie, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2)).1, 2