Primary neuroendocrine tumors of the kidney: Morphological and molecular alterations of an uncommon malignancy

Primary neuroendocrine (NE) tumors of the kidney (PNRTs) are rare and frequently mistaken for other renal and urothelial cancers. We evaluated morphological and molecular findings of 11 PNRTs classified according to the World Health Organization classification of lung NE tumors. Patients included 5 men and 6 women with a median age of 50 years. These tumors occurred in the left (5/11), right (3/11), and horseshoe (1/11) kidney. The histologic patterns were predominantly solid, trabecular, and pseudoglandular. Lymphovascular invasion and calcification were found in 3 and 1 cases, respectively. There were 2 atypical and 9 typical carcinoids. At the time of surgery, 2 patients with atypical carcinoids had hepatic metastasis, and 1 of the typical carcinoid patients had lymph node metastasis. All cases showed<1% proliferative rate, except 2 cases with hepatic metastasis, which showed 3% to 5% with MIB1/Ki-67 immunostaining. Immunostainings were frequently positive for synaptophysin, chromogranin, CD56, CD99, and neuron-specific enolase. Follow-up data (average 4 years) were available for 6 patients. Two patients with distant metastasis were alive with disease, and four patients with no metastasis were alive without disease. We evaluated the association of PNRT and loss of heterozygosity (LOH) on chromosome 3p21 and found LOH in 2 of 3 cases. However, the comparative genomic hybridization study (2/2) did not demonstrate significant chromosomal imbalances. We conclude that PNRTs are positive for NE markers and may have LOH on chromosome 3p21. PNRTs should be classified as NE tumors in other sites, and proliferative rate can be an indicator of aggressive behavior/metastasis.