Breast cancer can currently be categorized into three primary subtypes based on the expression of the estrogen and progesterone receptors (ER and PR) and HER2 (also known as ERBB2): luminal ER positive and PR positive (further divided into luminal A and B), HER2 positive, and triple-negative breast cancer (TNBC) [69, 70]. The gene discussed is PGR; the disease is breast cancer.