ERBB2 mutations are associated with worse prognosis, recurrence, and metastatic potential. ERBB2 may have a higher prevalence in CIS/non-papillary tumors. ERBB2 mutations have FDA-approved drugs available in other tumor types (non-urothelial) and active clinical trials within urothelial carcinoma. The gene discussed is ERBB2; the disease is in situ carcinoma.