Nested variant of urothelial carcinoma of the renal pelvis.

The nested variant of urothelial carcinoma is an uncommon form of urothelial carcinoma with distinctive histopathologic features. The majority of cases of this unusual type of urothelial carcinoma have been described in the urinary bladder, with examples of this neoplasm involving the upper urinary tract being extremely limited. The present report details the clinical and pathologic features of an unusual case of a nested variant of urothelial carcinoma occurring in the renal pelvis of a 71-year-old woman. The tumor was characterized by a nested pattern of growth and relatively bland cytologic features, and presented with locally advanced disease at the time of nephroureterectomy. Although rare, awareness that the nested variant of urothelial carcinoma may occur at this particular site is important so as not to confuse this unusual form of urothelial carcinoma with other pathologic lesions of the renal pelvis.