The Wilms' tumor gene (WT1) located at chromosome 11p13 was originally identified as a tumor-suppressor gene associated with Wilms' tumor, a kidney neoplasm of childhood. The WT1 gene encodes a zinc-finger transcription factor, which regulates target genes, some of which are related to cell differentiation, proliferation, and apoptosis, and binds to specific sequences within the promoter regions of the WT1 gene itself. It also binds to a number of other genes, such as insulin like growth factor-II, platelet-derived growth factor A chain, and IGH-I receptor. It has an essential role in the normal development of the urogenital system, and it is mutated in a small subset of patients with Wilms tumor. WT1 is altered in 1.72% of all cancers with non-small cell lung carcinoma, breast carcinoma, leukemia, colorectal adenocarcinoma, and melanoma having the greatest prevalence of alterations.