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A rare malignant renal tumor, typically affecting the pediatric population, characterized by an abnormal proliferation of cells that resemble the kidney cells of an embryo (metanephroma), leading to the term embryonal tumor.
ORPHA:654Classification level: Disorder
The annual incidence is estimated at about 1/10,000 births and it affects boys as well as girls.
Nephroblastoma mainly affects young children, between the ages 1 and 5 years, but 15% of nephroblastomas occur before the age of 1 year and 2% after the age of 8 years. Adult forms are very rare. An abdominal mass (unilateral in most cases) is frequently present. Patients sometimes experience abdominal pain (around 10% of cases), hypertension, fever (20% of cases), hematuria and anemia. The evolution of the disease is very rapid, with regional dissemination in the retroperitoneal space, lymph nodes, vessels (renal vein and inferior vena cava) and in the peritoneal cavity in cases of tumor effraction, and a strong likelihood of metastases in the lungs and liver.
Nephroblastoma is sporadic in 99% of cases and, among these cases, 10% are associated with congenital anomalies (aniridia, hemihypertrophy, genitourinary defects) or form part of specific syndromes (Beckwith-Wiedemann, Denys-Drash, WAGR or Perlman syndromes; see these terms). Genetic anomalies found in different chromosomal regions, including 11p13 (containing the WT1 gene), 11p15.5 (containing the H19 gene), 16q, 1p, 1q and 17p, have been found within the tumors. Familial forms are very rare (1% of cases) and are transmitted in an autosomal dominant fashion.
Diagnosis is based on imagery, particularly CT or MRI scans. The concentration of urinary metabolites of catecholamines is normal. Analysis of the extent of the disease is also conducted using imagery (ultrasound and abdominal CT analyzing particularly the liver and contralateral kidney, and thoracic radiography and CT).
Differential diagnoses include other renal tumors in children such as mesoblastic nephroma (especially in infants), clear cell sarcoma, neuroblastoma (extremely rare in the kidney but may invade the kidney by contiguity), rhabdoid tumors (see these terms) and metanephric stromal tumors.
Management and treatment
Disease management is multidisciplinary and may involve chemotherapy and surgery with or without radiotherapy. Chemotherapy enables preoperative reduction in tumor size and eradicates metastases. Surgery should be accomplished without tumor effraction, which usually means that total nephrectomy is required. Nephroblastoma can be confirmed on microscopic examination, which also allows the stage of the tumor in the kidney to be evaluated. This in turn determines the choice of post-operative chemotherapy. Radiotherapy is reserved for the most extensive cases or cases with the least favorable histology.
In the majority of cases, the prognosis is favorable with a survival rate of over 90%. Adult forms have the same prognosis and should be treated following the same methods, even when adult patients tolerate chemotherapy less well than children (which may lead to a reduction in treatment and as a result a worse prognosis).