Three clinically relevant biological BC subtypes (i.e., estrogens/progesterone receptor positive (ER+/PR+), human epidermal growth factor receptor 2 (HER2) amplified, and triple negative) and multiple molecular subtypes (e.g., Luminal A/B, HER2, basal like, normal like) with distinct features and clinical outcomes have been defined and characterized [2–5]. The gene discussed is PGR; the disease is breast cancer.