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RENAL MASSES

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Wilms Tumor

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Wilms tumor, also termed nephroblastoma, is the most common malignancy of the pediatric urinary tract, occurring in 7 to 10 per million children younger than 15 years. There are approximately 500 new cases of Wilms tumor annually in the United States.1 Wilms tumor accounts for approximately 6% of all pediatric malignancies and at least 85% of solid renal masses.2,3 It typically affects children under the age of 6, but is uncommon in young infants; the median age at presentation is 3.5 years. This tumor is rare in individuals over the age of 10 years.4,5 Worldwide, Wilms tumor occurs without a gender predilection. In the United States, however, the frequency is slightly higher among girls than among boys. The frequency of Wilms tumor is lower in Asians than in whites.4

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Treatment of unilateral Wilms tumor consists of nephrectomy and multimodality chemotherapy, with or without radiation therapy. In the United States, the standard treatment technique is nephrectomy at the time of diagnosis for all resectable lesions, followed by chemotherapy. Radiotherapy is useful for metastasis or residual disease, such as tumor spillage at the time of surgery or when there are known peritoneal tumor implants. Removal of metastatic lung nodules is sometimes indicated. In Europe, most patients receive several weeks of chemotherapy prior to nephrectomy, sometimes with percutaneous biopsy of the tumor at the time of diagnosis. The outcomes of these approaches are similar. Approximately 5% of patients with Wilms tumor have synchronous bilateral disease. The treatment approach to these children usually consists of an initial biopsy, subsequent chemotherapy, and delayed surgery. Surgery is tailored to preserve as much functional renal tissue as possible. The survival rate for these patients is similar to that of unilateral Wilms tumor.6–8

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Age at diagnosis, gender, tumor histology, and stage are important prognostic factors for patients with Wilms tumor. A younger age at diagnosis is associated with a greater likelihood of long-term survival. Unfavorable histology of Wilms tumor is more common in girls than in boys. The overall 5-year survival rate for Wilms tumor is approximately 90%.9 Stage 1 favorable histology is associated with a greater than 90% survival rate, regardless of tumor size.10 Children treated for Wilms tumor are at increased risk for second malignant neoplasms, with a cumulative incidence of 1.6%, representing more than 8 times the expected incidence.11 The risk of developing leukemia or lymphoma is greatest in the first 8 years after treatment; the risk of developing a solid tumor does not appear to diminish with time. Potential late effects of therapy include cardiotoxicity, renal dysfunction, and reproductive problems.8

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Wilms tumor is a genetically heterogeneous neoplasm that occurs as both a sporadic and a familial lesion. The sporadic form constitutes approximately 95% of Wilms tumor cases. Approximately 1% of children with Wilms tumor have a known ...

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