Breast cancer (BC) can be divided into three major classes based on genetic and histological evidence: - Breast cancer displaying hormone receptors (estrogen receptor (ER+)) or progesterone receptor (PR+), - Breast cancer exhibiting human epidermal receptor 2 (HER2+), and - triple-negative breast cancer (TNBC). The gene discussed is PGR; the disease is triple-negative breast carcinoma.