Originally described in association with Wilms tumor [153] (a kidney tumor), Wilms Tumor 1 (WT1), which plays a key role in urogenital development [154,155,156], is now more generally described as an oncogene in some cancer entities including leukemias [157] and also as tumor suppressor in others [158,159,160,161,162]. The gene discussed is WT1; the disease is leukemia.