Review of renal carcinoid tumor with focus on clinical and pathobiological aspects.

Renal carcinoid tumor is a rare neoplasm. In this article, we review this neoplasm with a focus on clinical and pathobiological aspects. The majority of patients present in the fourth to seventh decades, but there is no gender predilection. Clinically, patients with renal carcinoid tumor frequently present with abdominal, back or flank pain. This tumor is occassionally associated with horseshoe kidney and/or mature cystic teratoma located in the kidney. Macroscopically, these tumors are well demarcated with a lobulated appearance and yellow or tan-brown color cut surface. Microscopically, these tumors are composed of monomorphic round to polygonal cells with granular amphophilic to eosinophilic cytoplasm. Tumor cells are arranged in trabecular, ribbon-like, gyriform, insular, glandular and solid patterns. The nuclei are round to oval and with evenly distributed nuclear chromatin, frequently with a "salt and pepper"-pattern. Immunohistochemically, tumor cells demonstrate immuno-labeling for chromogranin A and synaptophysin. Ultrastructurally, the neoplastic cells contain abundant dense core neurosecretory granules. In previous genetic studies, abnormalities of chromosomes 3 or 13 have been reported. The clinical behavior of renal carcinoid tumors is variable, but is more indolent than most renal cell carcinomas. Further investigations are warranted in order to elucidate the critical genetic abnormalities responsible for the pathogenesis of this rare entity in renal neoplastic pathology.