PGR and breast cancer: There are five main types of breast cancer: luminal A-like (ER+, PR+, HER2-, low Ki-67), normal-like HER2- (lower ER+, PR+, HER2-, high Ki-67), luminal B-like HER2+ (ER+, PR+, HER2+, high Ki-67), HER2-enriched (ER-, PR-, HER2+, high Ki-67, non-luminal), and triple-negative (ER-, PR-, HER2-, high Ki-67) [4] (Figure 1B).