Renal cell carcinoma in children: histology, immunohistochemistry, and follow-up of 10 cases

Validation and utilization of a TFE3 break-apart FISH assay for Xp11.2 translocation renal cell carcinoma and alveolar soft part sarcoma

Background

Xp11.2 or TFE3 translocation renal cell carcinomas (RCC) and alveolar soft part sarcoma (ASPS) are characterized by chromosome translocations involving the Xp11.2 breakpoint resulting in transcription factor TFE3 gene fusions. The most common translocations documented in TFE3 RCCs are t(X;1) (p11.2;q21) and t(X;17) (p11.2;q25) which leads to fusion of TFE3 gene on Xp11.2 with PRCC or ASPL respectively. TFE3 immunohistochemistry (IHC) has been inconsistent over time due to background staining problems in part related to fixation issues. Karyotyping to detect TFE3 gene rearrangement requires typically unavailable fresh tissue. Reverse transcriptase-polymerase chain reaction (RT-PCR) is generally very challenging due to degradation of RNA in archival material. The study objective was to develop and validate a TFE3 break-apart fluorescence in situ hybridization (FISH) assay to confirm Xp11 translocation RCCs and ASPS.

Methods

Representative sections of formalin-fixed paraffin-embedded tissue blocks were selected in 40 possible cases. Approximately 60 tumor cells were analyzed in the targeted region. The validation of TFE3 FISH was done with 11 negative and two positive cases. Cut off for a positive result was validated as >7.15 % positive nuclei with any pattern of break-apart signals. FISH evaluation was done blinded of the immunohistochemical or karyotype data.

Results

Three out of forty cases were positive for the TFE3 break-apart signals by FISH. The negative cases were reported as clear cell RCC with papillary features (10), clear cell RCC with sarcomatoid areas (2), Papillary RCC with clear cell areas (9), Chromophobe RCC (2), RCC, unclassified type (3) and renal medullary carcinoma (1). 3 of the negative cases were consultation cases for renal tumor with unknown histology. Seven negative cases were soft tissue tumor suspicious for ASPS.

Conclusion

Our study validates the utility of TFE3 break-apart FISH on formalin-fixed paraffin-embedded tissue sections for diagnosis and confirmation of Xp11.2 translocation RCCs and ASPS.

Malignant renal tumors in children

Renal malignancies are common in children. While the majority of malignant renal masses are secondary to Wilms tumor, it can be challenging to distinguish from more aggressive renal masses. For suspicious renal lesions, it is crucial to ensure prompt diagnosis in order to select the appropriate surgical procedure and treatment. This review article will discuss the common differential diagnosis that can be encountered when evaluating a suspicious renal mass in the pediatric population. This includes clear cell sarcoma of the kidney, malignant rhabdoid tumor, renal medullary carcinoma and lymphoma.

WARM N COLD: malignant and benign renal tumors in children

Although Wilms tumor is the most common renal malignancy in children, the differential diagnosis is extensive and includes both malignant and benign disorders. We present a simple mnemonic-WARM N COLD, to aid in remembering these diverse tumors. Imaging clues including age of the patient, associated disease or syndrome as well as salient imaging characteristics such as bilaterality, and type or presence of metastasis are also presented and can help differentiate between these renal tumors of childhood.

Renal Cell Carcinoma in Children: Experience of a Single Center

OBJECTIVE

To evaluate the clinical features and outcome of children with renal cell carcinoma (RCC).

PATIENTS AND METHODS

Eleven patients with RCC who were diagnosed between 1972 and 2004 were retrospectively analyzed. Clinical features, histopathology, treatment regimens and outcomes of the patients were evaluated.

RESULTS

The male/female ratio was 3:8, with a median age of 10 years. The stage distribution was as follows: 3 patients in stage I, 1 patient in stage II, 3 patients in stage IIIb, and 4 patients in stage IV. Five of 7 patients with stage II-IV received an actinomycin D-based regimen, one received a cisplatin-based regimen, and the other was given 5-fluorouracil (5-FU). In the last patient, interferon-alpha was given in combination with 5-FU; 1 of the patients on the actinomycin D regimen received interferon-alpha as well. All of the stage I patients are alive without disease. Three patients with stage IIIb, stage IV and stage II disease are alive without disease 8, 14 and 26 years after their diagnosis, respectively. The other stage IV and stage IIIb patients died of the disease.

CONCLUSION

Nephroureterectomy is the main treatment modality, and it is sufficient for stage I patients. For patients with stage II-IV RCC, interferon-alpha and/or actinomycin D-based chemotherapy is the treatment of choice.

Clear cell renal cell carcinoma

Clear cell RCC is the most common type of RCC that occurs in adults. It has the worst prognosis among the common epithelial tumors of the kidney. Histologically, a wide range of morphologic patterns can be encountered. Those cases with a multi-locular cystic architecture are considered to be a distinct subtype because of the clinicopathologic features.

Renal cell carcinoma: case report and literature review

Renal cell carcinoma arising from epithelial cells of the renal tubule is a highly aggressive and malignant tumor in all ages. Less than 2% of cases occur in childhood, relatively in older age group. Only a few pediatric series have been presented in the English literature. Tumor is presented with characteristic findings of flank pain, gross hematuria, and palpable mass. Although one half of the patients have metastasis at the time of diagnosis, most cases are currently being incidentally detected using improved imaging techniques. The overall prognosis in children appears to be similar to that in adults. Tumor stage and complete surgical resection have been reported as the most meaningful prognostic factors for the outcome. The incidence of metastatic disease is same as in adults. The effect of chemotherapy and immunotherapy, either preoperatively or postoperatively, is unclear. Cure is the most likely consequence in localized and completely resected tumors. Here, we present an 8-year-old boy with renal cell carcinoma demonstrating only hematuria without any pathological physical examination findings. The mass was described by abdominal ultrasonography and computed tomography in the left kidney. After the left nephroureterectomy, the patient was given no therapy.

Morphologic and Molecular Characterization of Renal Cell Carcinoma in Children and Young Adults

A new WHO classification of renal cell carcinoma has been introduced in 2004. This classification includes the recently described renal cell carcinomas with the ASPL-TFE3 gene fusion and carcinomas with a PRCC-TFE3 gene fusion. Collectively, these tumors have been termed Xp11.2 or TFE3 translocation carcinomas, which primarily occur in children and young adults. To further study the characteristics of renal cell carcinoma in young patients and to determine their genetic background, 41 renal cell carcinomas of patients younger than 22 years were morphologically and genetically characterized. Loss of heterozygosity analysis of the von Hippel-Lindau gene region and screening for VHL gene mutations by direct sequencing were performed in 20 tumors. TFE3 protein overexpression, which correlates with the presence of a TFE3 gene fusion, was assessed by immunohistochemistry. Applying the new WHO classification for renal cell carcinoma, there were 6 clear cell (15%), 9 papillary (22%), 2 chromophobe, and 2 collecting duct carcinomas. Eight carcinomas showed translocation carcinoma morphology (20%). One carcinoma occurred 4 years after a neuroblastoma. Thirteen tumors could not be assigned to types specified by the new WHO classification: 10 were grouped as unclassified (24%), including a unique renal cell carcinoma with prominently vacuolated cytoplasm and WT1 expression. Three carcinomas occurred in combination with nephroblastoma. Molecular analysis revealed deletions at 3p25-26 in one translocation carcinoma, one chromophobe renal cell carcinoma, and one papillary renal cell carcinoma. There were no VHL mutations. Nuclear TFE3 overexpression was detected in 6 renal cell carcinomas, all of which showed areas with voluminous cytoplasm and foci of papillary architecture, consistent with a translocation carcinoma phenotype. The large proportion of TFE3 "translocation" carcinomas and "unclassified" carcinomas in the first two decades of life demonstrates that renal cell carcinomas in young patients contain genetically and phenotypically distinct tumors with further potential for novel renal cell carcinoma subtypes. The far lower frequency of clear cell carcinomas and VHL alterations compared with adults suggests that renal cell carcinomas in young patients have a unique genetic background.

Renal cell carcinoma with hemorrhagic cyst formation in a 4-year-old boy

We report on a case of renal cell carcinoma (RCC) with hemorrhagic cyst formation in a 4-year-old boy. The patient presented with asymptomatic macrohematuria. Abdominal ultrasound, computed tomography and magnetic resonance imaging demonstrated a left renal complicated cyst, 18 mm in diameter. Renal malignancy was suspected, and left radical nephrectomy was performed. Pathological diagnosis was a complicated cyst filled with bloody clots, with a wall composed of RCC. No metastases to the regional lymph nodes or other organs were found. This is an extremely rare occurrence of such a small RCC that developed a hemorrhagic cyst in a boy of this young age. The boy is being followed-up without any additional treatment.

Choroid plexus carcinoma presenting as an intraparenchymal mass

A 6-year-old girl with a history of a nondisplaced skull fracture diagnosed with computerized tomography (CT) scanning 3 years previously presented with a 6-week history of headaches and decreased use of her right side. On admission CT scans, a large cystic mass was identified in the left frontal lobe region of the brain. A connection between the mass and the ventricular system was not seen on radiological examination or during surgery. Gross-total resection of the mass was achieved. The histological and immunohistochemical findings in the resected tissue confirmed a diagnosis of choroid plexus carcinoma (ChPC). This is the first reported case of a ChPC arising in an extraventricular location not associated with the choroid plexus.

Expression of cytokeratin-18-related tissue polypeptide-specific (TPS) antigen in Wilms tumor

BACKGROUND

So far, there is no approved tumour marker for diagnosis or follow-up in Wilms tumour (WT). Tissue polypeptide-specific antigen (TPS), a cytokeratin 18 proteolytic fragment, has been suggested to be of value in the clinical management of WT patients. Cytokeratin 18 fragments are an early indicator of apoptosis and cytokeratin 18 might influence tumour cell behaviour. We investigated TPS expression in specimens of WT and other paediatric renal malignancies

PROCEDURE

Immunoreactivity of WT sections (n = 9), clear cell sarcomas (CCSK, n = 3), and a renal cell carcinoma (RCC), and two pediatric kidney tumour cell lines (WT: SK-NEP-1 and rhabdoid tumour of the kidney: G-401) were investigated using the monoclonal antibody M3. Additionally, immunoblotting and RT-PCR analysis were performed. Cell culture supernatants were evaluated for TPS release. Serum TPS was measured in five patients at diagnosis, during chemotherapy and after surgical resection.

RESULTS

Moderate to strong immunoreactivity for TPS was found in tubular and blastemal components of nearly all (8/9) WT specimens. This was confirmed by Western-blotting. Cystic and epithelial-like portions of CCSKs and RCC showed distinct reactivity (3/3). The supernatant of G-401 but not of SK-NEP-1 showed a time- and cell number-dependent increase of TPS release. Interestingly, TPS synthesis was demonstrated in SK-NEP-1 cells. Median preoperative serum TPS was elevated (293 U/l) compared to healthy children and lowest after surgical resection (49.5 U/l).

CONCLUSIONS

This is the first study demonstrating the synthesis and release of TPS by WTs and other paediatric renal malignancies. Considering the elevated levels of TPS in serum of these patients, a further investigation of this marker by larger clinical trials seems to be justified.

Treatment of childhood renal cell carcinoma with lymph node metastasis: two cases and a review of literature

Standard treatment for renal cell carcinoma (RCC) is radical nephrectomy with lymph node dissection. Stages I and II have encouraging prognoses, but Stage III with regional lymph node metastasis can be unfavorable. Adjuvant therapy for pediatric patients with advanced RCC with lymph node involvement or metastatic lesion has not been defined. Advanced pediatric RCC is reported in two patients (boys, aged 6 and 9 years: Stage IIIs, Robson; Stage III and IV, pTNM classification) treated by nephrectomy and lymph node dissection followed by postoperative interferon-alpha (IFN), that can be used as an adjuvant therapy with side effects such as fever, bone marrow suppression, or decreased liver function. One is doing well for 7 years, another is suffered from lung metastases at 3 years after surgery. Although immunotherapy is expected to improve survival in pediatric patients with advanced RCC, surgical resection of renal and metastatic tumors remains the standard treatment.

Pediatric renal masses: Wilms tumor and beyond

A variety of pediatric renal masses may be differentiated from Wilms tumor on the basis of their clinical and imaging features. Wilms tumor is distinguished by vascular invasion and displacement of structures and is bilateral in approximately 10% of cases. Nephroblastomatosis occurs most often in neonates and is characterized by multiple bilateral subcapsular masses, often associated with Wilms tumors. Renal cell carcinoma is unusual in children except in association with von Hippel-Lindau syndrome and typically occurs in the 2nd decade. Mesoblastic nephroma is the primary consideration in a neonate with a solid renal mass. Multilocular cystic renal tumor is suggested by a large mass with multiple cysts and little solid tissue. Clear cell sarcoma is distinguished by frequent skeletal metastases, and rhabdoid tumor is distinguished by its association with brain neoplasms. Angiomyolipoma frequently contains fat and is associated with tuberous sclerosis. Renal medullary carcinoma occurs in patients with sickle cell trait or hemoglobin SC disease and manifests as an infiltrative mass with metastases. Ossifying renal tumor of infancy is differentiated from mesoblastic nephroma by the presence of ossified elements. Metanephric adenoma lacks specific features but is always well defined. Renal lymphoma is characterized by multiple homogeneous masses, often with associated adenopathy.

Oncocytoid renal cell carcinoma after neuroblastoma: a report of four cases of a distinct clinicopathologic entity

Four children who developed oncocytoid renal cell carcinoma (RCC) after neuroblastoma are reported. One patient had multiple, bilateral RCCs. The mean age at time of diagnosis of RCC was 8.8 years (range, 5-13 years). The mean interval between neuroblastoma and RCC was 7.15 years (range, 3.1-11.5 years). The histologic findings of these RCCs did not fit within the spectrum of known renal epithelial neoplasms. Most of the neoplastic cells in all cases had eosinophilic, oncocytoid cytoplasm and were arranged in solid and papillary growth patterns. A subset of cells with reticular cytoplasm was also present. Immunohistochemical studies demonstrated keratins 8 and 18 in all neoplasms and keratin 20 in two cases. DNA ploidy analysis revealed that two of three neoplasms assessed were aneuploid. Cytogenetic studies revealed 45, XX, add or dup (7)(q32q36) in one neoplasm, and 83-89, XXXX, -1 ,-3, del (3)(q11.1q2?1), der(4)t(4;?22) (q32;q11.2), -14, -22 in a second tumor. Microsatellite polymerase chain reaction analysis detected no abnormalities in one neoplasm and allelic imbalance of chromosomes 2p31-32.2, 8p22, 9p22-24, 13q22, 20q13, and 22q11 in a second tumor. In case 4, two different RCCs excised 6 months apart were analyzed. The initial neoplasm showed allelic imbalance of chromosomes 2q31-32.2, 5q22, 5q31, 10p13-14, 13q22, 14q31, and 20q13. The subsequent neoplasm showed allelic imbalance of chromosomes 3p21.3, 14q31, and 20q13. The common presence of 14q31 and 20q13 abnormalities suggests that these two neoplasms were genetically related. In aggregate, these findings are distinctive, are not found in known types of RCC, and support the morphologic impression that oncocytoid RCC after neuroblastoma is a distinct clinicopathologic entity.

Renal-cell carcinoma in children: a different disorder from its adult counterpart?

BACKGROUND

Renal-cell carcinoma (RCC) is a rare tumor in children. To address whether RCC in children differs from its adult counterpart, we report a series of 16 children with RCC (5 boys, 11 girls, mean age 9.6 years, range 3-19 years) presenting between 1979 and 1996 at three pediatric centers.

PROCEDURE

Pathology showed papillary RCC in five patients (31%). Nonpapillary tumors were present in 11 (69%), of which nine were clear-cell type (56%), one was chromophobe-cell type (6%), and one was granular-cell type (6%). Cytogenetic studies were performed on four.

RESULTS

In two tumors, normal karyotypes (45,XX or 45,XY) were found. In another, there were translocations: t(X;1), t(X;2) and t(6;14). In the fourth, analysis revealed 46,XX/46,X,t(X;17)(p11.2;q25),t(1;12). Several features in this series differ from those reported in adults. In adults, RCC is more frequent in males, is usually nonpapillary, and is characterized cytogenetically by deletions or rearrangements in the short arm of chromosome 3. In contrast, in our series there was no male predominance and a higher proportion of papillary tumors. In addition, two of four cytogenetically analyzed tumors had translocations involving the X chromosome. Translocations involving the Xp11.2 locus have been infrequently reported in both adults and children with papillary RCC.

CONCLUSIONS

The higher frequency of papillary histology and the presence of translocations involving Xp.11.2 in two cases raise the possibility of a unique subtype of RCC in children.

Wilms' tumor with renal cell carcinoma overgrowth in a 3-year-old child

Wilms' tumors that contain features of both renal cell carcinoma and classic Wilms' tumor histology are rare. Even though nine such cases have been previously reported in the literature, we report the first case of a Wilms' tumor with an overwhelmingly renal cell carcinoma histologic pattern.

Metastatic renal carcinoma in a pediatric recipient of an adult cadaveric donor kidney

A 15-year old male with chronic renal failure secondary to obstructive uropathy received an adult cadaveric donor kidney. Evaluation for painless macroscopic hematuria occurring 2 years after transplantation disclosed a metastatic renal cell carcinoma, which by the use of restriction fragment length polymorphism analysis was shown to be of the donor's origin. Transplant nephrectomy and cessation of immunosuppressive therapy resulted in complete regression of multiple pulmonary metastases.

Immunohistochemical distribution pattern of intermediate filament proteins in 50 feline neoplasms

Twenty-eight epithelial and 22 nonepithelial feline tumors were studied immunohistochemically. Epithelial tumors were 10 squamous cell carcinomas, two basal cell tumors, two sebaceous gland carcinomas, three apocrine gland carcinomas, three thyroid papillary carcinomas, one thyroid solid carcinoma, one renal clear cell carcinoma, one renal papillary carcinoma, one endometrial carcinoma, and four lung bronchioloalveolar carcinomas. Nonepithelial tumors were 10 fibrosarcomas, one liposarcoma, one leiomyosarcoma, one rhabdomyosarcoma, one hemangiosarcoma, two mast cell tumors, one osteosarcoma, three melanomas, and two lymphomas. Commercially available antibodies directed against high- and low-molecular-weight keratins (keratin, RCK-102, NCL-5D3), vimentin, desmin, glial fibrillary acidic protein (GFAP), and neurofilament intermediate filament (IF) proteins were used in the avidin-biotin-peroxidase complex technique on formalin-fixed, paraffin-embedded tumor tissue samples. All epithelial tumors except the endometrial carcinoma expressed some type of keratin protein. Squamous cell carcinomas expressed high-molecular-weight keratins exclusively. Coexpression of high- and low-molecular-weight keratins was observed in one basal cell tumor, sebaceous and apocrine adenocarcinomas, and thyroid, renal, and lung carcinomas. In addition to keratins, vimentin immunoreactivity was found in all basal cell tumors, all sebaceous gland, thyroid papillary, renal, and lung adenocarcinomas, and one of the apocrine gland adenocarcinomas. Immunoreactivity with GFAP antibody was found in one basal cell tumor and one sebaceous gland adenocarcinoma. The endometrial carcinoma did not react with any of the antibodies applied. Nonepithelial tumors analyzed expressed either vimentin (fibrosarcomas, liposarcoma, haemangiosarcoma, mast cell tumors, osteosarcomas, melanomas) or vimentin and desmin (leiomyosarcoma, rhabdomyosarcoma, one fibrosarcoma) IF proteins exclusively. Lymphomas did not react with any of the antibodies employed. These findings indicate that IF proteins antibodies can be included in diagnostic panels of antibodies for immunocharacterization of feline tumors. In addition, they can be used as a basis for the diagnoses of poorly differentiated or undifferentiated feline neoplasms.

Anaplastic renal cell carcinoma following neuroblastoma

Renal cell carcinoma is unusual in children. We report a case of anaplastic renal cell carcinoma arising in a 7-year-old girl following treatment for Stage III neuroblastoma. The renal cell carcinoma has unusual histologic and ultrastructural features, which are discussed. The case is further unusual in that few children with advanced stage neuroblastoma survive long enough to develop second malignant neoplasms.

Renal cell carcinoma developing in the pediatric recipient of an adult cadaveric donor kidney

Renal cell carcinoma is an uncommon renal tumor in children, comprising between 1.8% and 6.3% of all malignant renal tumors of childhood (whereas renal cell carcinoma is the commonest renal tumor in adults). We describe a 15-year-old girl with chronic renal failure secondary to renal dysplasia and branchio-oto-renal syndrome, who received a cadaveric renal transplant at 8 years of age from a 25-year-old male donor. She developed severe chronic rejection 4 years after the transplant. A transplant nephrectomy was performed because of persistent gross hematuria. Histopathology of this graft showed chronic severe rejection and papillary necrosis. A fortuitous finding was a 1.5-cm renal cell carcinoma at one of the poles. We suggest that tumors which occur more commonly in adults and less commonly in children must be considered in children receiving adult organ transplants.

Renal cell carcinoma in children: a single institution's experience

Seven patients with renal cell carcinomas (RCC) were treated at the Department of Pediatric Oncology in Prague over a period of 15 years. The average age at diagnosis was 8 years 9 months. Histology review showed five tumors to be of clear cell type with mixed tubular, papillary, and solid patterns; one tumor was purely papillary eosinophilic type and one was composed of clear and eosinophilic cells. Five patients received chemotherapy and four of them also received radiotherapy. Four patients are without evidence of disease with a minimal follow-up period of 2 years. These four were all clinical stage I or II. Two stage III patients died of metastatic disease. One patient died of tumor emboli to the lungs at operation. Tumor diagnosis and treatment of the patients in the lower clinical stages seem to have a favorable prognostic impact in childhood RCC. Combined chemotherapy with vinblastine as one of the agents, and possibly additional immunotherapy, appears to have promising results, although the number of patients treated thus far is limited.

Distinctive patterns of renal neoplasms containing Tamm-Horsfall protein

Sections of 114 renal neoplasms from adults, and 2 renal rhabdoid tumours from children, were examined by an indirect immunoperoxidase method using two antibodies to Tamm-Horsfall protein. Forty-five of the adult neoplasms were also examined with an antibody to proximal tubular brush border. Tamm-Horsfall protein is normally only found in the cells of the thick limb of the loop of Henle, and there are widely divergent reports on its occurrence in renal neoplasms. In the present series, Tamm-Horsfall protein was detected in parts of 31 neoplasms. Four distinctive patterns of cell contained the protein: cells with a paranuclear inclusion typical of rhabdoid tumours; 'plasma rich' cells, which were large cells with cytoplasm that was centrally dense and peripherally clear; eosinophilic cells forming one type of papillary structure; and giant cells. The areas containing Tamm-Horsfall protein did not express markers of proximal tubular brush border, and appeared white to the naked eye, rather than the yellow of typical clear cell carcinomas. Tamm-Horsfall protein can therefore be found in renal neoplasms. The four distinctive patterns of positive cells appear to represent neoplastic phenotypes of thick limb cells. This has implications for the classification of renal neoplasms and for theories of their origin.

Spectrum of differentiation in pediatric epithelial tumors of kidney: report of two cases

Two unusual presentations of childhood renal cell epithelial tumors including one whose unique clinical manifestation was polycythemia are described. One was a renal cell carcinoma which was so poorly differentiated that ancillary histopathologic techniques were necessary to arrive at the correct diagnosis. The other case represented the opposite extreme being so well-differentiated as to raise the differential diagnosis of renal cell carcinoma versus renal cell adenoma with blastemal areas. These case studies exemplify the practical role for specialized histopathologic techniques in diagnosing pediatric renal tumors, which may not be feasibly or even accurately categorized into known renal tumor types using routine diagnostic methods.

Multicentric bilateral renal cell carcinomas and a vascular leiomyoma in a child

We report a unique case of multicentric bilateral renal cell carcinomas and a simultaneous large renal vascular leiomyoma in an 11-year-old child with sickle cell anemia. The patient presented with several episodes of massive hematuria. Abdominal sonography and computed tomography demonstrated bilateral renal neoplasms and the patient was clinically thought to have bilateral Wilms' tumor. An initial biopsy of the lower pole of right kidney revealed a renal cell carcinoma. Accordingly, bilateral renal angiography followed by right total nephrectomy and left upper pole partial nephrectomy were performed. Pathologic studies showed multicentric, bilateral renal cell carcinomas (two in the right kidney and one in the left kidney), of clear, granular, and oncocytic cell types. A simultaneous large vascular leiomyoma was also present in the right kidney. The smooth muscle nature of the leiomyoma was determined by light microscopy, immunohistology, and electron microscopy. The diagnostic difficulties in distinguishing them from other renal tumors are discussed.

renal tumors and tumor-like lesions in pediatric patients

Renal enlargement presenting as an abdominal mass(es) is attended by a lengthly differential diagnosis of non-neoplastic and neoplastic lesions with a range in serious connotations and consequences. Simple compensatory hypertrophy and unilateral multicystic dysplasia are relatively innocuous and easily recognized with appropriate imaging studies; they are also related in the sense that the normal contralateral kidney hypertrophies in the absence of a non-functioning dysplastic kidney. Bilateral nephromegaly in a neonate is generally a sign of autosomal recessive polycystic kidney disease or multicystic dysplasia secondary to distal obstructive uropathy. Primary neoplasms of kidney in the pediatric population in the past were traditionally classified as Wilms' tumors, but that erroneous practice has been eliminated with the recognition of several distinctive neoplasms in addition to classic Wilms' tumor. Separating a typical Wilms' tumor from mesoblastic nephroma, clear cell sarcoma of the kidney and the malignant rhabdoid tumor, for treatment and prognostic purposes, has become the accepted norm in the past 12-13 years. Another important advance at the cellular level is the recognition of a deletion in the short arm of chromosome 11 in the cultured cells of Wilms' tumor and in the germ cell line in certain clinical settings of Wilms' tumors. A dramatic expansion in the understanding and management of childhood renal neoplasms has occurred through the multimodality approach of laboratory investigation and applied clinical research.

Malignant renal tumors of childhood

The prognosis in nephroblastoma (Wilms' tumor) has been improved considerably by treatment protocols combining surgery, chemotherapy, radiation therapy, and, in some clinical trials, pre-operative chemotherapy. Cure is now achieved in most patients. All clinical trials have employed treatment strategies tailored to the individual risk of the patient, including the histological subtype of the tumor. In the National Wilms' Tumor Study (NWTS) of the United States these subtypes have been divided into two groups of tumors according to their "favorable" or "unfavorable" histology. At the Kiel Pediatric Tumor Registry we have devised a system which distinguishes three groups of tumors classified according to prognosis. The first group includes tumors with a favorable prognosis, even if only surgery is performed. These comprise congenital mesoblastic nephroma (CMN) and cystic, partially differentiated nephroblastoma (CPDN). The second group consists of tumors posing an intermediate risk, such as typical nephroblastoma and its histological variants characterized by variations in the relative proportions of the histological components. Fetal rhabdomyomatous nephroblastoma (FRN) is also included in this group. The third group comprises tumors of high risk such as anaplastic nephroblastoma, clear cell sarcoma of the kidney (CCSK), and malignant rhabdoid tumor of the kidney (MRTK). Since histological diagnosis plays a crucial role in the assignment of a patient to a particular type of treatment protocol, knowledge of the histological appearance of the various tumor types both with and without preoperative treatment is of utmost importance.