Triple-negative breast cancer (TNBC) tends to have the worst prognosis, with stage I tumors having a 5-year cancer-specific survival rate of 85% compared to 94% and 99% for HER2-positive and HR-positive breast cancers, respectively, and a stage IV median survival of 1 year for TNBC compared to a median of 5 years for HER2-positive and HR-positive tumors. The gene discussed is ERBB2; the disease is cancer.