A case of isolated mammary metastasis from surgically untreated urothelial vesical carcinoma is discussed. An integrated chemo-radiotherapeutical treatment had been planned, due to bad general condition; after this, an optimal subjective benefit and good objective response (reduction in lesion diameter < 50%, MR) were obtained. An isolated breast lesion appeared ten months after; its metastatic nature was only indirectly suspected by mammographic and echographic features. Only immunohistochemical study, realized on percutaneous needle biopsy specimen, definitively confirmed the urothelial metastatic origin. In present work, biological and prognostic significance of mammary metastases and the needing of distinguishing them from primary breast neoplasm are analysed, basing on the literature review.