ESR1 and metastatic neoplasm: Categorical variables included the affected breast (left or right), hormone receptor status (ER, PR, and HER2/neu), molecular subtypes (e.g., Luminal A, Luminal B, Basal-like), tumor grade (G1–G3), diagnostic categories (e.g., metastatic disease, primary tumor without metastasis, triple-negative status), and treatment protocols (anthracycline-based or platinum/taxane-based regimens).