Identification of genetically aberrant cell lineages in Wilms' tumors

Preparation of cells from formalin-fixed, paraffin-embedded tissue for use in fluorescence in situ hybridization (FISH) experiments

Numerical and structural chromosome abnormalities can be accurately detected in cells from archived tissues using fluorescence in situ hybridization (FISH). This unit describes two common approaches to performing FISH in formalin-fixed, paraffin-embedded tissue. The first approach utilizes 4 to 6 microm tissue sections in cases for which preserving tissue morphology is necessary, and the second involves extraction of intact nuclei from 50 microm tissue sections. To interpret FISH results using 4 to 6 microm sections, an adequate number of nuclei must be evaluated to perform statistical analysis. Evaluation of 30 to 50 nuclei from the single cell suspension generally gives an interpretable result.

Cytogenetically unrelated clones in different histologic components of a Wilms tumor

Wilms tumor (WT) is a triphasic malignant neoplasm comprised of variable proportions of epithelial, blastemal, and mesenchymal (stromal) elements. Cytogenetic analysis of these tumors has revealed a number of recurring abnormalities, including hyperdiploidy and structural abnormalities of chromosomes 1, 7, 11, and 16. We describe a WT in which apparently unrelated cytogenetic clones were detected at diagnosis, when the predominant histologic component was blastema, and after therapy, when the tumor was composed primarily of stroma. At diagnosis, a pseudodiploid karyotype was present, characterized by an X;14 insertion with concurrent deletion of 14q. In contrast, the post-therapy specimen had a hyperdiploid karyotype with a constellation of gains typical for WT. The presence of clonal abnormalities in both the blastemal and mesenchymal components of a WT supports the hypothesis that the stromal component is neoplastic, rather than reactive. The clonal abnormalities seen in different histologic components of the same WT are typically related or identical. The finding in this case of apparently unrelated clones is unusual. Possible etiologies for this biclonality, and clinical implications, are discussed.

Genetic changes of two Wilms tumors with anaplasia and a review of the literature suggesting a marker profile for therapy resistance

Cytogenetic data on Wilms tumors (WT) with anaplasia frequently associated with an unfavorable outcome are scarce. We present cytogenetic changes of two WT with anaplasia (primary tumor material) from nonresponders with a synopsis of the literature. The WT were investigated by cytogenetic analysis, comparative genomic hybridization, fluorescence in situ hybridization, immunofluorescence, and flow cytometric analyses. Both tumors exhibited characteristic genetic changes. One tumor was hypodiploid due to loss of entire chromosome 11; losses of 16p, 16q, 17p, chromosome 19 material, and loss of 22q12-qter. The other tumor was hyperdiploid and triploid, and displayed gain of 1q12-q23 and chromosome 9 material. Moreover, two morphological and genetically distinct cell lines have been established from both tumors, demonstrating underrepresentation of chromosomes 13, 14, 16, and 19. Karyotype descriptions of 120 WT with known clinical data together with data of this report confirm: (1) inter- and intratumor heterogeneity exists; (2) loss or underrepresentation of chromosome material at 11, 13, 14, 16, 17p, 19, and 22q in various combinations presents a new marker profile of resistance to cytotoxic agents regardless of the histological types; and (3) the prognostic impact of gain at 1q12-q23 sequences warrants further validation.

The expression pattern of Wilms' tumour gene (WT1) product in normal tissues and paediatric renal tumours

WT1, the Wilms' tumour suppressor gene located at chromosome 11p13, plays an important role in the development of the kidney. It is mutated in 10 per cent of Wilms' tumours (WTs) and their putative precursors called nephrogenic rests (NRs). A sensitive immunohistochemical technique was established to localize the WT1 gene product in archival normal tissues and paediatric renal tumour samples. Strong nuclear signal was seen in the various sites such as the kidneys, gonads, and decidua. Nuclear immunoreactivity of variable intensity was also seen in the skeletal muscle, smooth muscle of urinary bladder, ureter, and arteries. All 28 WTs (including the anaplastic variant) showed the WT1 gene product in a varying proportion of the blastema, epithelium, and stroma. The anaplastic nuclei in six WTs showed an intensity of staining comparable to their adjacent favourable histology counterparts. All the intralobar and perilobar types of NR demonstrated the WT1 gene product. All three malignant rhabdoid tumours were positive, while three of four mesoblastic nephromas and a clear cell sarcoma were negative. These findings provide an insight into the interrelationships of these renal tumours.