[Neuroendocrine tumors of the kidneys].

The 2004 World Health Organization (WHO) classification of renal cancer includes renal carcinoid and neuroendocrine cancer of the kidneys in the group of primary renal neuroendocrine tumors. The histological features of primary renal carcinoids are similar to those of neuroendocrine tumors found in other anatomical locations. Primary carcinoid tumors of the kidneys are frequently misdiagnosed as other kidney cancers, such as papillary renal cell carcinoma, mesonephric tumors, Wilms tumor (WT) and undifferentiated carcinoma. Immunohistochemical staining results are consistent with the diagnosis of a neuroendocrine tumor with immunoreactivity for synaptophysin, chromogranin, CD56, and neuron-specific enolase (NSE). Positive expression of CD99 can also be seen. There is mainly absence of WT1, cytokeratin 7, cytokeratin 20, thyroid transcription factor (TTF1) and LCA, ruling out most other differential diagnoses. Renal carcinoid tumors are regarded as low-grade neuroendocrine tumors; however, many studies have demonstrated metastatic disease in patients with renal carcinoid tumors. The prognostic value of histological parameters is uncertain. Some studies have correlated poor patient prognosis with increased mitotic activity, presence of necrosis and cytological atypia. Cases with higher mitotic rates of > 2 mitoses/10 high power fields (HPF) developed metastases more frequently; therefore, the WHO classification of neuroendocrine tumors used in other organs is recommended for primary renal carcinoid tumors.