ERBB2 and breast cancer: These findings suggest that ERBB2 amplification and mutation is often a later event in urothelial cancer pathogenesis and not present in all tumor cells in a significant minority of patients with urothelial cancer, which contrasts with breast cancer, a disease in which ERBB2 amplification has been shown to be an early initiating event and highly concordant between primary and metastatic disease sites42,43.