Breast cancer is primarily classified based on the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), into subtypes including hormone receptor-positive (HR+) breast cancer, HER2+ breast cancer, and triple-negative breast cancer (TNBC)2, 3. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.