Nephroblastic tumors include nephroblastoma, the most common, and cystic partially differentiated nephroblastoma.
Nephroblastoma is a malignant tumor which comprises more than 85% of pediatric renal tumors and 5% of childhood cancers.
It is usually found in children 2–4 years old, it is relatively uncommon in the first 6 months of life and in children older than 6 years, whereas it is rare in the neonatal period. Nephroblastoma rarely occurs in adults.
There is no gender predilection.
Five percent of the tumors are multicentric and bilateral.
Tumor resection followed by chemotherapy or adjuvant chemotherapy and surgical treatment are the two different protocols of therapy.
Despite the different managements, the overall survival currently is more than 90%.
The associations with cryptorchidism, hypospadias, other genital anomalies, hemihypertrophy, and aniridia are well-recognized and described in different genetic syndromes such as Beckwith-Wiedemann, Wilms-aniridia-genital anomaly-retardation (WAGR), and Denys-Drash syndromes due to different genetic alterations.
It presents as a mass usually larger than 5 cm with solid, soft, and grayish or pinkish, resembling brain tissue. Hemorrhage and necrosis are frequently present. The tumor is usually surrounded by a prominent pseudocapsule composed of compressed renal and perirenal tissues. Cystic tumors macroscopically indistinguishable from cystic nephroma which present small foci of blastema, immature appearing stromal cells, and primitive epithelium are classified as cystic partially differentiated nephroblastoma (Beckwith et al. 1990).
The blastema component is usually positive for WT1 and may label for desmin and not for the other muscular markers. The epithelial components are positive for WT1 and cytokeratins, including CK7.
The WT1 gene located on chromosome 11p13 is involved in the pathogenesis of the WAGR (Wilms tumor associated with aniridia, genital anomalies, and mental retardation) and the Denys-Drash (pseudohermaphroditism, severe glomerulopathy, and Wilms tumor) syndromes. The WT1 gene is mutated in approximately 20% of sporadic nephroblastomas. Nephroblastomas demonstrating loss of heterozygosity for chromosomes 1p and 16q have been shown to have a poor prognosis (Huang et al. 2009).
The differential diagnosis includes small blue cell tumors (neuroblastoma, rhabdomyosarcoma, and primitive neuroectodermic tumor), immature teratoma, metanephric adenoma, and papillary renal cell carcinoma. The differential diagnosis is based on the morphological features in association with an immunohistochemical panel such as WT1, CD99, CD57, myogenin, and chromogranin.
Nephrogenic rests are abnormally persistent foci of embryonal cells that are potentially able of developing into nephroblastoma (Wilms tumor). Nephrogenic rests can be found adjacent to nephroblastoma or in the surrounding renal parenchyma (Beckwith et al. 1990).