ESR1 and breast cancer: Tumors positive for key breast cancer markers, including ER-positive (ER+) (Figure 1C), BRCA protein expression-positive (BR+) (Figure 1D), and HER2-negative (HER2-) (Figure 1E), exhibited significantly higher PLCH1 expression compared to their respective negative counterparts (ER−, BR−, HER2−) (Figures 1C-E, all P < 0.0001).