Wilms Tumor
Clear Cell Sarcoma
Rhabdoid Tumors of the Kidney
Mesoblastic Nephroma
Renal Cell Carcinoma
Nephroblastomatosis
Neuroepithelial Tumors of the Kidney
Desmoplastic Small Round Cell Tumor of the Kidney
Cystic Partially Differentiated Nephroblastoma
Multilocular Cystic Nephroma
Primary Renal Synovial Sarcoma
Anaplastic Sarcoma of the Kidney

Note: Some citations in the text of this section are followed by a level of evidence. The PDQ editorial boards use a formal ranking system to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. (Refer to the PDQ summary on Levels of Evidence ¹ for more information.)

Although most patients with a histologic diagnosis of Wilms tumor fare well with current treatment, approximately 10% of patients have histopathologic features that are associated with a poorer prognosis, and, in some types, with a high incidence of relapse and death. Wilms tumor can be separated into three prognostic groups on the basis of histopathology:

• Favorable histology: Histologically, Wilms tumor mimics development of a normal kidney consisting of three cell types: blastemal, epithelial (tubules), and stromal. Not all tumors are triphasic, and monophasic patterns may present diagnostic difficulties. While associations between histologic features and prognosis or responsiveness to therapy have been suggested, with the exception of anaplasia, none of these features have reached statistical significance and therefore do not direct the initial therapy.[1]
• Anaplastic histology: Anaplastic histology is the single most important histologic predictor of response and survival in patients with Wilms tumor. There are two histologic criteria for anaplasia, both of which must be present for the diagnosis. They are the presence of multipolar polyploid mitotic figures with marked nuclear enlargement and hyperchromasia. Anaplasia correlates best with responsiveness to therapy rather than to aggressiveness. It is most consistently associated with poor prognosis when it is diffusely distributed and when identified at advanced stages. This is the reason why focal anaplasia and diffuse anaplasia are differentiated, both pathologically and therapeutically. Focal anaplasia is defined as the presence of one or a few sharply localized regions of anaplasia within a primary tumor. Focal anaplasia does not confer a poor prognosis, while diffuse anaplasia does.[2-4]
• Nephrogenic rests: Many Wilms tumors appear to arise from abnormally retained embryonic kidney precursor cells arranged in clusters termed nephrogenic rests. The term nephroblastomatosis is defined as the presence of diffuse or multifocal nephrogenic rests. There are two types: intralobar nephrogenic rests and perilobar nephrogenic rests. Diffuse hyperplastic perilobar nephroblastomatosis is defined as nephroblastomatosis forming a thick rind around one or both kidneys and is considered a preneoplastic condition.[1] Patients with any type of nephrogenic rest in a kidney removed for nephroblastoma should be considered at increased risk for tumor formation in the remaining kidney. This risk decreases with patient age.[5]

Clear cell sarcoma of the kidney (CCSK) is not a Wilms tumor variant, but it is an important primary renal tumor associated with a significantly higher rate of relapse and death than favorable–histology Wilms tumor. In addition to pulmonary metastases, clear cell sarcoma also spreads to bone, brain, and soft tissue. The classic pattern of CCSK is defined by nests or cords of cells separated by regularly spaced fibrovascular septa.[6] Previously, relapses have occurred in long intervals after the completion of chemotherapy (up to 10 years), however with current therapy relapses after 3 years are uncommon.[7] The brain is a frequent site of recurrent disease.[8,9]

Rhabdoid tumors (RTs) are extremely aggressive malignancies that generally occur in infants and young children. The most common locations are the kidney and central nervous system (CNS) (atypical teratoid/rhabdoid tumor), although RTs can also arise in most soft-tissue sites. Initially they were thought to be a rhabdomyosarcomatoid variant of Wilms tumor when they occurred in the kidney.

Histologically, the most distinctive features of rhabdoid tumors of the kidney (RTK) are rather large cells with large vesicular nuclei, a prominent single nucleolus, and in some cells, the presence of globular eosinophilic cytoplasmic inclusions. A distinct clinical presentation with fever, hematuria, young age (mean 11 months), and high tumor stage at presentation suggests a diagnosis of RTK.[10] RTK tends to metastasize to the lungs and the brain. As many as 10% to 15% of patients with RTK also have CNS lesions.[11]

RTs in all anatomical locations have a similar molecular origin. Mutation or deletion of both copies of the hSNF5/INI1 gene that maps to chromosome band 22q11.2 is observed in approximately 70% of primary tumors. An additional 20% to 25% of tumors have reduced expression at the RNA or protein level, indicative of a loss-of-function event. The INI1 protein is a component of the SWI/SNF chromatin remodeling complex (a group of genes involved in cell signaling, growth, and differentiation). Identical mutations may give rise to a brain or kidney tumor. Germline mutations of INI1 have been documented for patients with one or more primary tumors of the brain and/or kidney, consistent with a genetic predisposition to the development of rhabdoid tumors.[12,13] In most cases, the mutations are de novo, and not inherited from a parent. Germline mosaicism has been suggested for several families with multiple affected siblings. It does appear that those patients with germline mutations have the worst prognosis.[14]

Mesoblastic nephroma (MN) comprises about 5% of childhood kidney tumors. The median age of diagnosis is 2 months and more than 90% of cases appear within the first year of life. Twice as many males are diagnosed as females. The diagnosis should be questioned when applied to individuals older than 2 years. When diagnosed in the first 7 months of life, the 5 year event-free survival (EFS) and overall survival (OS) rates are 94% and 96%, respectively.[15]

Grossly, MNs appear as solitary, unilateral masses indistinguishable from nephroblastoma. Microscopically, they consist of spindled mesenchymal cells. They can be divided into two major types: classic and cellular. Classic MN is often diagnosed by prenatal ultrasound or within 3 months after birth and closely resembles infantile fibromatosis.[16] Infantile fibrosarcoma and cellular MN contain the same t(12;15)(p13;q25) chromosomal translocation suggestive of a potential linkage.[17] The risk for recurrence within MN is closely associated with the presence of a cellular component and with stage.[16]

Malignant epithelial tumors arising in the kidneys of children account for more than 5% of new pediatric renal tumors; therefore, they are more common than CCSK or RTK. Renal cell carcinoma (RCC), the most common primary malignancy of the kidney in adults, occurs rarely in children younger than 15 years. In the older age group of adolescents (aged 15–19 years), approximately two-thirds of renal malignancies are RCC.[18] The annual incidence rate is approximately 4 per 1 million children compared with an incidence of Wilms tumor of the kidney that is at least 29-fold higher. RCC in young patients has a different genetic and morphologic spectrum than that seen in older adults.[19-22] RCC may be associated with von Hippel-Lindau (VHL) disease, a hereditary condition in which blood vessels within the retina and cerebellum grow excessively.[19] The gene for VHL is located on chromosome 3p25-26 and is a tumor-suppressor gene whose function is lost in patients with the syndrome. Screening for the VHL gene is available.[23] RCC has also been associated with tuberous sclerosis, a hereditary disease characterized by benign fatty cysts in the kidney.[24,25] In tuberous sclerosis, the renal lesions may actually be epithelioid angiomyolipoma (also called perivascular epithelioid cell tumor or PEComa), which is associated with aggressive or malignant behavior and expresses melanocyte and smooth muscle markers.[26,27] Familial RCC has been associated with an inherited chromosome translocation involving chromosome 3.[25] A high incidence of chromosome 3 abnormalities has also been demonstrated in nonfamilial renal tumors. RCCs have been described in patients several years after diagnosis and therapy for neuroblastoma.[28] A rare subtype of RCC, renal medullary carcinoma, may be associated with sickle cell hemoglobinopathy.[29] Renal medullary carcinomas are highly aggressive malignancies characterized clinically by a high stage at the time of detection, with widespread metastases and lack of response to chemotherapy and radiation therapy.[30][ Level of evidence: 3iiA] Survival is poor and ranges from 2 weeks to 15 months, with a mean survival of 4 months.[29-31][Level of evidence: 3iiA]

Pediatric RCC differs histologically from the adult counterparts. Although the two main morphological subgroups of papillary and clear cell can be identified, about 25% of RCCs show heterogeneous features that do not fit into either one of these categories. Childhood RCCs are more frequently of the papillary subtype (20%–50% of pediatric RCCs) and can sometimes occur in the setting of Wilms tumor, metanephric adenoma, and metanephric adenofibroma.

Translocation-positive carcinomas of the kidney are recognized as a distinct form of RCC and may be the most common form of RCC in children. They are characterized by translocations involving the transcription factor E3 (TFE3) located on Xp11.2. The TFE3 gene may partner with one of the following three genes: (ASPL)-TFE3, renal cell carcinoma papillary 1 gene (PRCC)-Xp11.2, or the transcription factor EB (TFEB) gene on chromosome 6p21. The translocations involving TFE3 and TFEB induce overexpression of these proteins which can be identified by immunohistochemistry. These RCCs are characterized by advanced stage at presentation (N+, M0) but have a favorable short-term prognosis with surgery alone.[19,22,32-34]

RCC may present with an abdominal mass, abdominal pain, or hematuria. In a series of 41 children with RCC, the median age was 124 months with 46% presenting with localized stage I and stage II disease, 29% with stage III disease, and 22% with stage IV disease using the Robson classification system. The sites of metastases were the lungs, liver, and lymph nodes. EFS and OS were each about 55% at 20 years post treatment. Patients with stage I and stage II disease had an 89% OS rate, while those with stage III and stage IV disease had a 23% OS rate at 20 years posttreatment.[24] An important difference between the outcomes in children and adults with RCC is the prognostic significance of local lymph node involvement. Adults presenting with RCC and involved lymph nodes have a 5-year OS of approximately 20%, but the literature suggests that 72% of children with RCC and local lymph node involvement at diagnosis (without distant metastases) survive their disease.[35] In another series of 49 patients from a population-based cancer registry, the findings were essentially confirmed. In this series, 33% of the patients had papillary subtype, 22% had translocation type, 16% were unclassified, and 6% had clear-cell subtype. Survival at 5 years was 96% for patients with localized disease, 75% for patients with positive regional lymph nodes, and 33% for patients with distant metastatic RCC.[36]

Some nephrogenic rests may become hyperplastic which may produce a thick rind of blastemal or tubular cells that enlarge the kidney. The diagnosis may be made radiographically, most readily by magnetic resonance imaging, in which the homogeneity of the hypointense rind-like lesion on contrast-enhanced imaging differentiates it from Wilms tumor. Biopsy often cannot discriminate Wilms tumor from these hyperplastic nephrogenic rests. If left untreated, they may regress. Differentiation may occur following the administration of chemotherapy. Current recommendations are for treatment with vincristine and dactinomycin until nearly complete resolution as determined by imaging. Even with treatment with vincristine and dactinomycin, about half of children will develop Wilms tumor, within an average of 36 months after diagnosis. In a series of 52 patients, three patients died of recurrent Wilms tumor.[37] In treated children, as many as one-third of Wilms tumors are anaplastic, probably as a result of selection of chemotherapy-resistant tumors, so early detection is critical. Patients are followed by imaging at a maximum interval of 3 months for a minimum of 7 years. Given the high incidence of bilaterality and the subsequent Wilms tumors, renal-sparing surgery is indicated.[37] These patients will be eligible for treatment on the COG-AREN0534 ² trial with vincristine and dactinomycin.

Neuroepithelial tumors of the kidney (NETK) are extremely rare and demonstrate a unique proclivity for young adults. It is a highly aggressive neoplasm, more often presenting with penetration of the renal capsule, extension into the renal vein, and metastases.[38,39] Primary NETK consist of primitive neuroectodermal tumors characterized by CD99 (MIC-2) positivity and the detection of EWS/FLI-1 fusion transcripts. Within NETK, focal, atypical histologic features have been seen including clear cell sarcoma, RT, malignant peripheral nerve sheath tumors, and paraganglioma.[38,40] (Refer to the PDQ summary on Ewings Family of Tumors ³ for more information about neuroepithelial tumors.)

Desmoplastic small round cell tumor of the kidney (DSRCT) is a rare, small, round blue tumor of the kidney. It is diagnosed by its characteristic EWS-WT1 translocation.[41] (Refer to the PDQ summary on Childhood Soft Tissue Sarcoma Treatment ⁴ for more information about DSRCT.)

Cystic partially differentiated nephroblastoma is a rare cystic variant of Wilms tumor (1%) with unique pathologic and clinical characteristics. It is composed entirely of cysts and their thin septa are the only solid portion of the tumor. The septa contain blastemal cells in any amount with or without embryonal stromal or epithelial cell type. Several pathologic features distinguish this neoplasm from standard Wilms tumor. Patients with stage I disease have a 100% survival rate with surgery alone. Patients with stage II disease have an excellent outcome with tumor resection followed by postoperative vincristine and dactinomycin.[5]

Multilocular cystic nephromas (MCNs) are benign lesions consisting of cysts lined by renal epithelium. These lesions can occur bilaterally and a familial pattern has been reported. MCN has been associated with pleuropulmonary blastomas, so radiographic imaging studies of the chest should be followed in patients with MCN.[42] Recurrence has been reported following tumor spillage at surgery.[43][Level of evidence: 3iiiA]

Primary renal synovial sarcoma (PRSS) is a subset of embryonal sarcoma of the kidney and is characterized by the t(x;18)(p11;q11) SYT-SSX translocation. It is similar in histology to the monophasic spindle cell synovial sarcoma. PRSS contains cystic structures derived from dilated, trapped renal tubules. PRSS occurs more often in young adults and this type of renal tumor should be treated with different chemotherapy regimens than traditional Wilms tumor.[44]

Anaplastic sarcoma of the kidney is a rare renal tumor that has been identified mainly in patients younger than 15 years. Patients present with a renal mass with the most common sites of metastases being the lung, liver, and bones. These tumors show pathologic features similar to pleuropulmonary blastoma of childhood (see the PDQ summary on Unusual Cancers of Childhood ⁵ for more information) and undifferentiated embryonal sarcoma of the liver (see the PDQ summary on Childhood Liver Cancer ⁶ for more information). Optimal therapy for this diagnosis is not clear. In the past, these tumors have been identified as anaplastic Wilms tumor and treated accordingly.[45]

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Glossary Terms

Consecutive case series (not population-based) with total mortality as an endpoint. See Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®) for more information.

Nonconsecutive case series with total mortality as an endpoint. See Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®) for more information.