ER + /HER2- breast cancer is the most common subtype, constituting about 70% of the cases; the ER-/HER2 + subtype constitutes about 15–20%, and the ER-/PR-/HER2- subtype (triple-negative breast cancer [TNBC]) constitutes about 15%4,5. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.