A case report of renal cell tumor in a 45-year-old female mimicking lower portion nephrogenesis.

This report describes a renal tumor with an unusual histology in a 45-year-old woman. The tumor was white in color, different from usual renal cell carcinoma, and mainly consisted of variously shaped tubules formed by flat or cuboid cells within marked edematous stroma. Elaborated branching or tubules arranged in a papillary pattern with focal spindle-shaped cell proliferation were characteristic features. Immunohistochemical staining expressed diffusely positive for vimentin and S-100 protein, partially positive for cytokeratin and epithelial membrane antigen and negative for Leu-M1, Leu-7, CD34 and markers for muscle cells. Ultrastructural studies of the tumor cells showed adenocarcinoma-like characteristics. According to these histological, immunohistochemical and electron microscopy findings, it is suggested that this tumor be designated as unclassified renal cell carcinoma with histology mimicking lower-nephron nephrogenesis.