By the other hand, AR is expressed in about 80% of primary breast cancers, particularly in triple-negative breast cancer (TNBC), characterized by lack of expression of estrogen receptor 1 (ER), progesterone receptor (PR), and human epidermal growth factor receptor type 2 (HER2) [7], and associated with a poor prognosis [8]. The gene discussed is PGR; the disease is breast cancer.