Study of childhood renal tumours using antisera to fibronectin, laminin, and epithelial membrane antigen

Hyaluronan and angiogenesis

Remodelling tissues, in both normal and pathological situations, show a greatly increased synthesis and turnover of hyaluronan. An essential part of these processes is new blood vessel formation. Whereas native hyaluronan has been reported to inhibit angiogenesis in vivo, partial degradation products (4-25 disaccharide units) have been found to stimulate angiogenesis in several in vivo systems. Examination of the effect of hyaluronan and its oligosaccharides on cultured cells suggests that these effects are due to the direct action of hyaluronan on endothelial cells. Native HA inhibits endothelial cell proliferation and disrupts cell-cell/cell-substrate interactions at physiological concentration. Angiogenic oligosaccharides induce both endothelial proliferation and migration, possibly via a receptor-mediated mechanism. Thus the metabolic state of hyaluronan could have profound effects on tissue neovascularization.

Applications of immunogold labeling in ultrastructural pathology

This review provides an update on the use of postembedding immunogold labeling, preferentially of the protein A-gold technique, for electron microscopic research in diseased states. In the first part, some helpful antigen recovery techniques for use of immunogold labeling of ultrathin sections prepared from routinely aldehyde (and osmium tetroxide) fixed and conventionally epoxy resin-embedded tissue are cited. In the second part, selected applications for studies of tumor cell surface conjugates, such as polysialic acid in Wilms tumor, proinsulin-insulin conversion in human insulinoma, and the importance of pre-Golgi intermediates for retention of a misfolded polypeptide hormone in a protein misfolding disease, are discussed.

Expression ofPAX 3 alternatively spliced transcripts and identification of two new isoforms in human tumors of neural crest origin

The developmental gene PAX 3 is expressed in the early embryo in developing muscle and elements of the nervous system, including the brain. Since no one has investigated the expression of the isoforms of PAX 3 in the neuroectodermal tumors melanoma and small cell lung cancer (SCLC), we have carried out a comprehensive screening for the expression of the isoforms PAX 3a-e using RT-PCR in human melanoma cell lines, primary human ocular and secondary cutaneous melanomas. We have identified 2 new isoforms of PAX 3, g and h, which we have isolated, cloned and sequenced. Sets of primers for each isoform were designed and their specificity was confirmed by sequence analysis of the products. The isoforms PAX 3a-e were detected in all human cutaneous melanoma cell lines (8/8), but only PAX 3c (1/2) and PAX 3d (2/2) in ocular melanoma cell lines. The same PAX 3 isoforms were detected in more than 80% of human cutaneous melanomas: PAX 3a and b (15/17), PAX 3c (14/17), PAX 3d (16/17) and PAX 3e (15/17). In contrast the results for 7 SCLC cell lines were PAX 3a (0/7), PAX 3b (1/7), PAX 3c (3/7), PAX 3d (6/7), PAX 3e (2/7); 8/8 cutaneous melanoma cell lines and 8/8 ocular melanoma tissues, together with 14/17 cutaneous melanoma tissues screened, expressed the new isoform PAX 3g. All 8 cutaneous melanoma cell lines expressed PAX 3h, but it was not detectable in any of the tumor tissues (0/20). Neither of the 2 ocular melanoma cell lines expressed the 2 new isoforms. Comparison of the different amplicon staining intensities on a gel suggests that PAX 3c and PAX 3d are the predominant transcripts expressed, with relatively low expression of PAX 3e and PAX 3h. We propose that these and the 2 new isoforms we have discovered may be important in oncogenesis and differential diagnosis of melanomas or SCLC.

MUC1 mucin and trefoil factor 1 protein expression in renal cell carcinoma: correlation with prognosis

This study examines the coexpression of MUC1 mucin and trefoil factor 1 (TFF1) and their relationship to progression of renal cell carcinoma (RCC). Immunohistochemistry was performed on tumor and adjacent normal tissue from clear-cell RCC (n = 60) and tissues from normal controls (n = 5) using a set of well-characterized monoclonal antibodies recognizing different epitopes of MUC1 and TFF1. Results of immunohistochemistry were compared with clinical parameters, including tumor grade, tumor size, presence of metastasis, and progression-free survival of patients after surgery. In normal tissue, MUC1 and TFF1 were absent from the normal proximal tubular epithelium but were identified in distal and collecting tubular epithelium. In RCC, increased MUC1 expression positively correlated to tumor progression. MUC1 recognized by HMFG1 was associated with large tumor size (P < .05), distant metastasis (P < .05), and invasion of large veins (P < .05). Expression of the under-glycosylated form of MUC1 recognized by SM3 was found to correlate to time to progression (recurrence, metastasis, or death of patient; P < .001). Expression of TFF1 did not significantly correlate with any prognostic parameters. However, there was a significant correlation (P < .01) between TFF1 and MUC1 expression (HMFG2 epitope) in RCCs. These results are consistent with the following conclusions: (1) MUC1 may be an independent prognostic marker in RCC; (2) TFF1 is frequently coexpressed with MUC1 and may act synergistically; and (3) RCC may originate from distal tubular epithelium.

Renal cell carcinoma with rhabdoid features

Neoplasms with rhabdoid features have been reported at many anatomic sites. In the kidney, rhabdoid tumors are typically found in children, whereas only rare examples have been reported in adults. Little is known of renal cell carcinomas (RCCs) that exhibit rhabdoid features. The objective of this study was to determine the incidence of RCC with rhabdoid attributes and characterize the histologic, immunophenotypic, and ultrastructural features by retrospective analysis of 480 consecutively identified cases of RCC in radical nephrectomy specimens. Immunohistochemical evaluation was performed in cases with rhabdoid foci using a panel of antibodies to pancytokeratin (pan-CK), CK7, CK20, epithelial membrane antigen (EMA), S-100 protein, desmin, vimentin, neuron-specific enolase (NSE), muscle-specific actin (MSA), smooth muscle actin (SMA), human melanoma, black-45 (HMB-45), and glial fibrillary acidic protein (GFAP). Electron microscopy was also performed in selected cases. The presence and extent of rhabdoid foci in relation to pathologic stage and grade were assessed. Twenty-three of 480 cases of RCC (4.7%) exhibited rhabdoid features. The 23 patients were all adults with a mean age of 61.8 years (age range, 33-84 yrs). Fifteen of the patients were men and eight were women. Histologically, the rhabdoid foci were typified by sheets and clusters of variably cohesive, large epithelioid cells with vesicular and often eccentric nuclei, prominent nucleoli, and large, paranuclear intracytoplasmic hyaline globules (inclusions). The presence of these rhabdoid features was related to high histologic Fuhrman grade of the nonrhabdoid carcinoma component, with an incidence of 0 of 84 grade I cases, eight of 300 grade 2 cases (2.6%), six of 70 grade 3 cases (8.9%), and nine of 26 grade 4 cases (34.6%; p = 3 x 10(-9)). The rhabdoid foci were all high grade. The presence of rhabdoid foci was also found in higher stage carcinomas. A total of 52% (12 of 23) of RCC cases with rhabdoid features exhibited extrarenal extension compared with 28% (24 of 92) of contemporary RCCs without rhabdoid features (p = 0.03). The size of the rhabdoid component ranged from 1 mm to more than 2 cm and comprised 1% to 50% of the renal mass. Immunoreactivity for vimentin (100%), NSE (79%), and panCK (56%) was present in the majority of cases. Substantial percentages of cases were immunopositive for EMA (47%) and S-100 protein (37%), with minimal to no immunohistochemical reactivity for CK7 (5%), SMA (5%), CK20 (0%), desmin (0%), MSA (0%), HMB-45 (0%), and GFAP (O%). A distinctive globular, paranuclear reaction pattern was found for the cytokeratin, EMA, and vimentin immunostains. Ultrastructurally, the rhabdoid cells had paranuclear intermediate filament aggregates or paranuclear condensation of organelles, often associated with peripheral vacuolization. Adult RCCs may harbor a rhabdoid component, and these neoplasms can be regarded as "composite" tumors. Rhabdoid elements are important to identify because of their high-grade nature, and association with high stage. Adult RCC with rhabdoid elements should be distinguished from pure rhabdoid tumors of kidney, in light of their clinicopathologic differences. Rhabdoid differentiation in adult renal cell carcinoma may represent clonal divergence and/ or evolution, and emergence of a particularly aggressive element.

The value of ultrastructural evaluation in the diagnosis of renal tumors: a general overview

The understanding of renal neoplasia has advanced significantly in the last 20 years. New challenges have arisen as a consequence of prolonged dialysis and renal transplantation becoming the therapeutic modes to deal with chronic renal disease. Immunosuppression resulting from primary disease processes or as a result of clinical intervention has resulted in an increase in neoplasia in general and changes in manifestations and clinical behavior of tumors. Special techniques such as immunocytochemistry and electron microscopy have provided information that has resulted in refinement of diagnostic and conceptual issues. The variable gross and histological manifestation of many of the renal neoplasms can be explained at least in part by reflecting on the new fundamental knowledge that has been acquired regarding renal developmental biology. A more aggressive approach from a therapeutic point of view placing emphasis on specific treatment protocols for the various nosologic entities further emphasizes the need to understand the advances that have taken place in the field. This article provides an overview of the subject, with emphasis on an overall conceptual understanding, to serve as a practical framework. The articles that follow address the specific current role of ultrastructure in the diagnosis and understanding of renal neoplasms.

Distribution of extracellular matrix glycoproteins in the human mesonephros

We analyzed the expression and distribution of collagen types IV and VI, laminin and fibronectin during the development and regression of the mesonephros in human embryos and fetuses ranging from 6 to 12 weeks of gestation by indirect immunoperoxidase methods. Type IV collagen, laminin and fibronectin were detected along the glomerular, tubular and capsular basement membranes of developing and mature nephrons. Only type IV collagen and fibronectin were found in the mesangium. Type VI collagen formed a delicate interstitial fibrillar network and a continuous basement membrane-like structure along the mesonephric nephrons. Basement membranes (GBM) of developing and mature glomeruli showed a distinct continuous staining for this collagen. The mesangial matrix was rich in type VI collagen. Mesonephric involution started during the 8th week of gestation and coincided with a moderate expansion of mesangial matrix and progressive collapse of the capillary walls, while the tubules became thinner and shorter. Staining for all extracellular matrix glycoproteins studied showed GBM wrinkling, gradual disintegration of some capillary loops and glomerulosclerosis. The sclerotic glomeruli were strongly positive for type IV collagen and less positive for type VI collagen and fibronectin. Laminin was absent. Our results indicate that collagen types IV, VI, laminin and fibronectin may be involved in the development and regression of the human mesonephros.

A new in vitro model of murine mesoderm migration: the role of fibronectin and laminin

Examination of the factors involved in primary mesodermal migration in the mouse has been complicated by the lack of a suitable in vitro model. We have developed a new culture system using primitive streak stage embryos denuded of primitive endoderm, which allows easy observation and manipulation of the outgrowing cells. The cells migrating away from these explants were shown by immunocytochemistry to express vimentin and an epitope of the I antigen recognised by the antibody C6, both of which are present on the newly emerged mesoderm and not on the embryonic ectoderm in sections of embryos in utero. Conversely, cytokeratin, stage-specific embryonic antigen 1 (SSEA-1), E-cadherin and desmoplakin are expressed by the embryonic ectoderm but lost during mesoderm formation in vivo. They are absent or expressed very weakly by the migrated cells in vitro. In addition, only explants of the ectoplacental cone (EPC) and visceral endoderm alone, expressed a carbohydrate epitope (recognised by monoclonal antibody BOO6), characteristic of the EPC and primitive endoderm in utero, but absent from mesoderm. Thus we conclude that the cells which outgrow in this system are indeed mesodermal in phenotype. We have confirmed the work of others in demonstrating the presence of fibronectin (FN) and laminin (LN) in the migratory path of the mesoderm, at the ectoderm-visceral endoderm interface. We also report that the beta 1 integrin subunit of the FN and LN receptor is expressed by mesodermal cells at this interface. Using our in vitro model we have examined the role of the extracellular matrix (ECM) in mesodermal migration. Mesodermal cells migrate further and faster on substrates coated with FN or LN, and this increased migration is abolished by appropriate blocking antibodies. We conclude that the ECM, in particular FN and LN, plays an important role in the migration of primary mesodermal cells during gastrulation in the mouse embryo.

Successful treatment for a metastatic supratentorial malignant rhabdoid tumor

The case of a boy with a familial history of Rendu-Osler disease, who successively developed a cerebellar pilocytic astrocytoma (at 3 years of age) and a metastatic supratentorial malignant rhabdoid tumor (at the age of 12 years) is reported. After a complete surgical removal, the CSF was cleared by 4 courses of chemotherapy, and the child received a craniospinal irradiation. He is currently alive and well 19 months after completion of the treatment. The authors discuss the ethiopathogeny of such intracranial tumors and argue for aggressive treatment.

Congenital mesoblastic nephroma: an immunohistochemical and lectin study

Eight cases of congenital mesoblastic nephroma (CMN) were examined. Three CMNs were of the classical (typical) variant, two were cellular (atypical), and three showed a mixed pattern. A panel of nephron segment-specific tubular epithelial markers (the lectins Tetragonolobus purpureas, Phaseolus vulgaris erythroagglutinin, and Arachis hypogaea and antibodies to epithelial membrane antigen, cytokeratin, and Tamm-Horsfall protein) were used to differentiate epithelial structures within the tumor. Antibodies against vimentin, desmin, and muscle-specific actin were used as mesenchymal markers. A monoclonal antibody to the long (embryonic) form of polysialic acid (PSA) on the neural cell adhesion molecule was used as a putative renal oncodevelopmental marker. An antibody to proliferating cell nuclear antigen also was applied, which revealed increased proliferative rate in cellular CMNs. In addition to clearly entrapped native renal tubules, CMNs contain tubular structures with immature, dysplastic epithelium and occasional epithelial cell clusters embedded deep within the tumor. These immature tubules and clusters express distal nephron, including collecting duct markers and, occasionally, vimentin and PSA. We propose that these primitive tubules and epithelial structures may originate from the ureteric bud. An epithelial differentiation of the tumor cells also is possible. In one pure cellular CMN and two mixed CMNs the cellular component showed diffuse staining for PSA. The PSA (neural cell adhesion molecule) expression of the cellular component suggests that CMN may originate from the uninduced nephrogenic mesenchyme.

Clear cell sarcoma of the kidney expresses insulinlike growth factor-II but not WT1 transcripts

Two cases of clear cell sarcoma of the kidney (CCSK), five Wilms' tumors (WTs), and three fetal kidneys were studied by molecular hybridization to elucidate the histogenesis of CCSK. Northern blot and in situ hybridization demonstrated that all the CCSKs, WTs, and fetal kidneys contained abundant insulinlike growth factor-II (IGF-II) transcripts, whereas WTs and fetal kidneys--but not CCSKs--showed significant expression of WT1 gene, a candidate tumor suppressor gene implicated in the etiology of WTs. Comparative analysis of in situ hybridization of IGF-II and WT1 transcripts in CCSKs and fetal kidneys revealed that CCSK cells showed similar hybridization patterns to primitive metanephrogenic blastemal cells and early stromagenic cells. The data strongly suggest that CCSK is distinct from WT and may be derived from undifferentiated metanephrogenic blastemal cells with potential to differentiate into a stromal cell lineage. The result also suggests that this unique tumor should, more appropriately, be known as stromal--rather than clear--cell sarcoma of the kidney.

Congenital mesoblastic nephroma: possible prognostic and management value of assessing DNA content

The case records and pathology of all children with kidney tumours treated in the West Midlands Health Authority Region (WMHAR) from 1957 to 1986 were reviewed. The histology was reviewed by a panel of three paediatric pathologists. Thirteen (6%) out of 211 cases were considered to have congenital mesoblastic nephroma (CMN). Nine were of the conventional type, three of the atypical cellular type, and one mixed. DNA ploidy was investigated and showed two of the tumours to be aneuploid and nine diploid (tissue was not available in the two other cases). The two aneuploid tumours were of atypical cellular and mixed histology, respectively; the diploid tumours were of the conventional type in eight cases and atypical cellular in one. The atypical cellular type has been reported to behave more aggressively, but the benefit of additional treatment after surgery to prevent recurrence remains unclear. Measurement of DNA content by flow cytometry, together with histological subclassification, may be useful in selecting patients who will benefit from further treatment after surgery.

Recurrent renal cell carcinoma arising in Wilms' tumor

A 19-month-old black girl had a radical nephrectomy for a Wilms' tumor that contained areas of epithelium indistinguishable from renal cell carcinoma. She was treated with chemotherapy but subsequently had pulmonary metastases develop and massive abdominal recurrence. The recurrent tumor was histologically renal cell carcinoma with no identifiable Wilms' tumor elements. The child died with recurrent and metastatic tumor 13 months after nephrectomy. Pathologic, immunoperoxidase, and flow cytometric studies of this unusual case are presented.

Malignant rhabdoid tumor of the orbit

Malignant rhabdoid tumor (MRT), originally described as a sarcomatous variant of Wilms' tumor, is now recognized as a distinct, highly malignant entity. The authors describe, for the first time, a primary tumor of the orbit with histologic, immunohistochemical, and ultrastructural features of MRT. Their findings suggest both epithelial and mesenchymal differentiation of this unique tumor.

Sera of children with renal tumours contain low-molecular-mass hyaluronic acid

The molecular mass of hyaluronic acid (HA) rather than its serum concentration alone may be a hallmark of certain types of malignancy. A radiometric assay was used to measure HA levels in 35 children with renal tumours [33 Wilms' tumours and 2 bone metastasizing renal tumours of childhood (BMRTC)] and 20 normal siblings of children with cancer. The HA level in the sera of normal children was barely detectable and had a molecular mass of 1-5 x 10(5). In both Wilms' and BMRTC patients, very high levels of HA were found in preoperative serum samples; these fell dramatically following surgical excision of the tumours. A novel finding of our study was the presence of low-molecular-mass HA (similar to the angiogenic fragments of HA) in the sera of BMRTC patients. In contrast, high-molecular-mass HA (which is not angiogenic) was found in the sera of Wilms' patients (2 x 10(6) kDa). Following surgery in BMRTC patients, not only did serum HA levels fall to a value within normal ranges, but also the HA which remained was of high molecular mass.

Malignant rhabdoid tumour of the kidney expressing neurofilament proteins. Immunohistochemical findings and histogenetic aspects

A malignant rhabdoid tumour (MRT) of the kidney was studied immunohistochemically using a large panel of monoclonal antibodies. All tumour cells were marked by a vimentin antibody. Variable amounts of the tumour cells were stained by antibodies specific for neurofilament proteins. Keratin, desmin and GFA, however, were not expressed. Antibodies reacting with lymphohaematopoietic antigens as well as with normal renal tissue and renal neoplasms, especially Wilms' tumours, (BA-1, BA-2, BA-3) and an antibody directed against Tamm-Horsfall protein failed to stain the tumour. These results, especially the expression of neurofilaments demonstrated for the first time in a MRT, point to a derivation of the demonstrated tumour from the neural crest. Analysis of the heterogeneous immunohistological marker expression and of the different primary sites of MRTs suggest that these highly malignant neoplasms are a histogenetically heterogeneous group, irrespective of their characteristic light microscopic appearance.

Anaplastic Wilms' tumor and other clinically aggressive childhood renal neoplasms: ultrastructural and immunocytochemical features

The ultrastructural and immunocytochemical findings in a series of 32 rarely encountered childhood renal malignancies are reviewed. The discussion includes anaplastic Wilms' tumors, renal clear cell sarcomas, rhabdoid tumors, carcinomas, sarcomas, neuroendocrine tumors, and lymphomas. An attempt is made to assess the relative merits of these two techniques in the differential diagnosis of these often troublesome lesions.

A monoclonal antibody stains blastemal but not tubular components of Wilms' tumour

The monoclonal antibody PAL-E is specific for endothelial cells in a wide variety of normal and tumour tissue. In normal kidney, PAL-E reacts exclusively with the endothelium of non-glomerular blood vessels. In Wilms' tumour, binding of PAL-E was not restricted to the endothelium; staining of blastemal cells was observed in seven out of eight cases examined. Mesenchymal and tubular components, if present in Wilms' tumour, were negative. In contrast, a monoclonal antibody to Factor VIII-related antigen (RFF-8-R-1) bound only to endothelial cells in these tumours. In fetal kidney, PAL-E binding showed a wider distribution than in adult kidney and both stromal and glomerular capillaries were stained. Tubules and non-endothelial stromal cells were negative. These results indicate that the reactivity of the monoclonal antibody, PAL-E, is not restricted to cells of endothelial origin in all tissues. The implications of these findings for the differentiation of Wilms' tumour are discussed.

Primary rhabdoid tumour of the brain

A posterior fossa tumour in a 3 year old child is presented with characteristic histological, ultrastructural and immunohistochemical features of rhabdoid tumour. Many tumour cells contained cytoplasmic eosinophilic hyaline inclusions. Ultrastructurally concentric whorls of 10 nm intermediate filaments were identified. Immunohistochemical staining disclosed vimentin, cytokeratin and epithelial membrane antigen positivity. Renal and extrarenal rhabdoid tumours have been well documented but a primary rhabdoid tumour of the brain is extremely rare. Additional ultrastructural features seen were tubular crystalline inclusions in endoplasmic reticulum and abnormal large mitochondria.

Study of childhood renal tumours using a monoclonal antibody to Tamm-Horsfall protein

A monoclonal antibody to Tamm-Horsfall glycoprotein was used for the immuno-localization of Tamm-Horsfall protein in formalin fixed, paraffin embedded tissue sections of childhood renal tumours, normal children's kidneys, and human fetal kidneys. The procedure was a dinitrophenyl hapten sandwich staining method. The antibody, diluted 1/100,000, gave a very strong and specific staining of the loop of Henle and distal tubules of normal and fetal kidneys. No staining was seen in Wilms' tumour, mesoblastic nephroma, and bone metastasizing renal tumour of childhood. In contrast, two of seven renal carcinomas and three of four rhabdoid renal tumours were positive for Tamm-Horsfall protein.

A cell line from Wilms' tumour with deletion in short arm of chromosome II

A cell line (T3/73) from a Wilms' tumour has been established from a 9 month-old boy with aniridia. The tumour was removed in 1973. On histological examination a diagnosis of Wilms' tumour was made which showed undifferentiated areas, marked tubule formation and abundant striped muscle fibres. The tumour cells, which are fusiform, grew rapidly in culture without the addition of growth factors, and have undergone over 100 passages. Approximately 95% and 5% were positive for desmin and cytokeratin, respectively. The cell doubling time was 28 hr. Cytogenetic studies revealed a karyotype of 46,XY,del(11) (p12::p14). Although the cells stained very intensely with a monoclonal antibody that detects oncogene ras p 21 antigen, Southern blot analysis using c-Ha-ras as a probe failed to reveal an obvious deletion or amplification of either Ha-ras allele.

The distribution of cytokeratin antigens in the kidney and in renal tumours

The distribution of cytokeratin antigens during embryogenesis of the kidney and in 57 renal tumours has been studied using immunocytochemical techniques. A polyclonal antiserum to epidermal prekeratins and the monoclonal antibodies CAM 5.2 and PKK1 have been used to identify cytokeratins of different molecular weights. The ureteric bud-derived structures expressed large molecular weight cytokeratins. The tubular component of the kidney expressed cytokeratins detected by CAM 5.2 and PKK1. During glomerular development there was transient expression of low molecular weight cytokeratins by the visceral glomerular epithelium but in the adult kidney only the parietal epithelium expressed cytokeratins. Tubules in nephroblastomas contained low molecular weight cytokeratins but the blastema did not. Some ureteric bud-derived structures were identified in six nephroblastomas. Renal carcinomas expressed low molecular weight cytokeratins. Four collecting duct carcinomas were studied; these all expressed the large molecular weight cytokeratins found in collecting duct epithelium. These results indicate that the cytokeratin phenotype of renal tumours is unchanged from that of the normal epithelial cells.

Ultrastructure and histogenesis of the renal tumors of childhood: an overview

This review discusses the ultrastructural and immunohistochemical features of the common childhood renal tumors, with an emphasis on their diagnostic usefulness. Speculations regarding their histogenesis also are presented, with the hope that these may serve to diminish some of the confusion surrounding the classification of these morphologically diverse lesions.

Study of childhood renal tumours using peroxidase conjugated lectins

Six peroxidase conjugated lectins were used to compare their ability to bind to formalin fixed paraffin embedded tissue sections of childhood renal tumours (Wilms' tumour, mesoblastic nephroma, renal carcinoma, rhabdoid renal tumour, and bone metastasising renal tumour of childhood (BMRTC) with fetal and normal children's kidney. Lectins were found to be helpful in the differential diagnosis of renal tumours. Another important finding was that the mesenchyme of renal tumours showed differences in its reactivity among various types of kidney tumours. The results of lectin binding were not helpful in establishing the origin of kidney tumours.