HER2 overexpression in our particular case was paradoxically a confusing factor when asserting the urothelial nature of the tumor—because of the higher frequency of HER2 overexpression in breast cancer—and a mean to further ensure the identity of primary UC and breast metastasis thanks to the concordance between the immunochemical and molecular features of both lesions. The gene discussed is ERBB2; the disease is neoplasm.