Microcystic urothelial cell carcinoma with neuroendocrine differentiation arising in renal pelvis. Report of a case.

Microcystic urothelial cell carcinoma is a rare variant of urothelial cell carcinoma which occurs in the bladder and, rarely, in the renal pelvis. Neuroendocrine differentiation is uncommon in pure urothelial carcinoma and is more frequently found in neoplasms with glandular differentiation. We report a case of microcystic urothelial cell carcinoma arising in renal pelvis and showing focal neuroendocrine differentiation. A 55-year-old man with a history of non-small cell cancer of the lung presented with abdominal pain and hematuria. Imaging studies and gross examination revealed a partially cystic mass in the left kidney. Microscopic examination disclosed invasive carcinoma with prominent microcystic features, with microcysts lined by low columnar and flat cells. Immunohistochemical analysis confirmed the urothelial histotype (positive for thrombomodulin, p63 and high-molecular-weight cytokeratins) and disclosed focal neuroendocrine differentiation.