Adult mesoblastic nephroma

We report a case of asymptomatic mesoblastic nephroma in a 54-year-old woma n. The tumor showed immunohistochemical reactions similar to developing nep hrons. Electron microscopy showed immature tubules with numerous intracytop lasmic intermediate filaments. Recent studies support the concept of pathog enesis of the mesoblastic nephroma originating from collecting ducts. Howev er, this case exhibited a complex pattern of antigenic expression not restr icted to the collecting ducts, but including the glycoprotein CD24 and the neural cell adhesion molecule (NCAM). The following differential diagnoses will be discussed: benign mixed epithelial and stromal tumor, metanephric a denoma, and nephrogenic adenofibroma.