Multicentric papillary adenocarcinoma of the renal pelvis and ureter. Report of a case with ultrastructural study.

A case of multicentric papillary adenocarcinoma arising in the renal pelvis and proximal ureteral mucosa of a 35-year-old man is presented. The left nephrectomy specimen demonstrated multiple, fungating, papillary tumors. The largest tumor measured 10 X 9 X 6 cm and invaded the renal parenchyma. Smaller tumors with long stalks were found. Microscopically, the papillary fronds of each neoplasm were lined by a single layer of cuboidal to low columnar epithelium admixed with a few areas of invasive tubular adenocarcinoma. The adjacent pelvic mucosa was the site of cuboidal epithelial metaplasia. The ultrastructure of both the papillary tumor and the pelvic mucosa suggested that they originated from the nonmucigenic metaplastic epithelium with a partial similarity to the lining of the proximal convoluted tubule. The growth pattern and the multicentric development of this unusual neoplasm suggest that this is a case of the malignant counterpart of the nephrogenic adenoma in the kidney and ureter, and reflect a biologic behavior corresponding to ordinary urothelial papillary tumors.