ESR1 and cancer: For hormone receptor status (ER and PR), HER2 expression, Ki-67 proliferation index, cancer type (IDC vs. ILC vs. DCIS), and luminal subtype, none of the four parameters reached statistical significance in group comparisons (all p ≥ 0.209) and Spearman correlations with these variables were uniformly weak (|ρ| ≤ 0.165, all p > 0.05).