Low-grade myxoid renal epithelial neoplasms with distal nephron differentiation

We report 4 distinctive renal epithelial neoplasms that are essentially ide ntical at the morphologic and immunohistochemical levels and do not fit an accepted category in the existing classification of these lesions. The pati ents were all females, with ages ranging from 32 to 79 years (mean, 50 year s). The tumors were well circumscribed and were composed of uniform, predom inantly low cuboidal cells with eosinophilic, focally vacuolated cytoplasm, Tumor cells gener ally formed interconnecting tubules, with smaller areas of cordlike growth and spindling in a bubbly, myxoid stroma. Ah tumors were confined to the kidney, and all were immunoreactive for high-molecular-wei ght cytokeratin 34 beta E12, cytokeratin 7, epithelial membrane antigen, an d cytokeratin cocktail AE1/3. Only 1 tumor was focally immunoreactive for U lex euopaeus agglutinin. Ultrastructural study showed tumor cells forming t ubular structures reminiscent of the loop of Henle or distal convoluted tub ule. Follow-up in all 4 cases was benign, These distinctive tumors may be c onfused with aggressive sarcomatoid renal cell carcinomas because of their spindled morphology. The morphologic, immunohistochemical, and ultrastructu ral features of these lesions indicate differentiation toward distal nephro n segments. Similar tumors probably have been reported among low-grade coll ecting duct carcinomas or tumors "possibly related to the loop of Henle." C opyright (C) 2001 by W.B. Saunders Company.