Wilm's Tumor (WT), a sporadic and familial childhood kidney tumor, is genetically heterogeneous. Wilms' tumor is associated with mutations of WT1, a zinc-finger transcription factor that is essential for the development of the metanephric kidney and the urogenital system. The WT1 gene is normally expressed in fetal kidney and mesothelium, and its expression has been suggested as a marker for Wilms tumor and mesothelioma.