This methodology delineates critical biomarkers, including the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), utilized to categorize breast cancer into five subtypes: luminal A, luminal B, HER2 positive, triple-negative breast cancer (TNBC), and normal-like [14,15]. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.