also known as Nephroblastoma.
Most cases occur in children between 2 and 5 years of age
WAGR syndrome, characterized by aniridia, genital abnormalities, and mental retardation
Denys-Drash syndrome (DDS) also has an extremely high risk (∼90%) of developing Wilms' tumor. This syndrome is characterized by gonadal dysgenesis and renal abnormalities
abnormalities of the Wilms' tumor 1 (WT1) seen in both of the above syndromes
Beckwith-Wiedemann syndrome (BWS), also has an increased risk of developing Wilms' tumor. These patients have enlargement of individual body organs (e.g., tongue, kidneys, or liver) or entire body segments (hemihypertrophy); enlargement of adrenal cortical cells (adrenal cytomegaly)
large, solitary, well-circumscribed mass, although 10% are either bilateral or multicentric at the time of diagnosis. On cut section, the tumor is soft, homogeneous, and tan to gray, with occasional foci of hemorrhage, cystic degeneration, and necrosis
triphasic combination of blastemal, stromal, and epithelial cell types is observed in most lesions
Sheets of small blue cells, with few distinctive features, characterize the blastemal component.
Epithelial "differentiation" usually takes the form of abortive tubules or glomeruli.
Stromal cells are usually fibrocytic or myxoid in nature, although skeletal muscle "differentiation" is not uncommon.
Rarely, other heterologous elements are identified, including squamous or mucinous epithelium, smooth muscle, adipose tissue, cartilage, and osteoid and neurogenic tissue
Approximately 5% of tumors contain foci of anaplasia (cells with large, hyperchromatic, pleomorphic nuclei and abnormal mitoses). The presence of anaplasia correlates with underlying p53 mutations, and the emergence of resistance to chemotherapy
Nephrogenic rests are putative precursor lesions of Wilms' tumors and are sometimes present in the renal parenchyma
resemble Wilms' tumors (hyperplastic rests) to sclerotic rests consisting predominantly of fibrous tissue .