Low-grade tubular-mucinous renal neoplasm with neuroendocrine differentiation: a histological, immunohistochemical and ultrastructural study.

Low-grade tubular-mucinous renal neoplasm (LGTMRN) was recently established as a distinct carcinoma classification. A 70-year-old, female traffic accident victim underwent a detailed examination that disclosed a huge mass in the lower pole of the left kidney. The patient underwent a nephrectomy based on a diagnosis of renal tumor. Macroscopically, the tumor was well demarcated and a whitish color with focal hemorrhage. Histological examination showed that tumor cells proliferated through tubular, trabecular, and solid growth patterns in the mucinous background. Focally, foci of clear cells or the proliferation of spindle cells was also observed. Nuclei were generally round and uniform in size. No abnormal mitotic figures were identified. Immunohistochemically, tumor cells were diffusely positive for AE1/AE3, vimentin and chromogranin A, and focally positive for cytokeratin (CK) 18, CK19, Ulex europaeus agglutinin-1, epithelial membrane antigen, neuron-specific enolase (NSE), CD9 and CD57. Ultrastructurally, tumor cells contained a moderate number of mitochondria, rough endoplasmic reticulum and dense-core granules. No renin granules or glycogen were observed. Microvilli were focally seen. Our results render further evidence that LGTMRN is a distinct entity from the hitherto established renal neoplasms. Foci of clear cells and neuroendocrine differentiation should be added to the histological spectrum of LGTMRN.