PGR and breast cancer: Based on these biomarkers, BC can be classified into five intrinsic subtypes: Luminal A (ER+, PR+, HER2-, low Ki-67), Luminal B/HER2-negative (ER+, PR-/+, HER2-, low Ki-67), Luminal B/HER2-positive (ER+, PR-, HER2+, high Ki-67; or ER+, PR+, HER2+, low Ki-67), HER2-positive (ER-, PR-, HER2+, any Ki-67), and triple-negative BC (TNBC) (ER-, PR-, HER2-, any Ki-67) [4].