Deletion of WT1 and WIT1 genes and loss of heterozygosity on chromosome 11p in Wilms tumors in Japan

Diagnostic utility of Wilms' tumour-1 protein (WT-1) immunostaining in paediatric renal tumours

Background & objectives:

Renal tumours constitute about 7 per cent of all neoplasms in children. It is important to differentiate Wilms’ tumour (commonest tumour) from non-Wilms’ tumours. The aim of this study was to evaluate the immunoexpression and diagnostic role of Wilms’ tumour-1 protein (WT1) in paediatric renal tumours.

Methods:

A total of 53 cases of renal tumours in children (below 18 yr) who underwent total nephrectomy were included in this retrospective study. WT1 immunostaining was done using mouse monoclonal WT1 antibody (clone: 6F-H2).

Results:

Of the 53 cases, 38 (72%) were of Wilms’ tumour. Non-Wilms’ group (15) included six cases of mesoblastic nephroma (MN), two each of clear cell sarcoma (CCSK), renal cell carcinoma (RCC) and peripheral neuroectodermal tumour (PNET) and one each of angiomyolipoma (AML), rhabdomyosarcoma (RMS) and malignant rhabdoid tumour (MRT). Proportion of WT1 positivity in Wilms’ tumour was 100 per cent in contrast to 26.7 per cent in non-Wilms’ tumours (P<0.001). Epithelial and blastemal components of Wilms’ tumour showed moderate (2+) nuclear and cytoplasmic staining in 80 (24/30) and 75 per cent (24/32) cases, respectively. MN, PNET, CCSK and AML were negative for WT1. RMS, RCC and MRT showed cytoplasmic staining, strongest in RMS. No significant association was seen between WT1 expression and NWTSG (National Wilms’ Tumor Study Group) stage.

Interpretation & conclusions:

WT1 helps to differentiate Wilms’ tumour from other paediatric renal tumours. It may help in differentiating the two subgroups of Wilms’ tumour which have distinct molecular pathogenesis and biological behaviour, however, further prospective studies are required for validation of this hypothesis.

Mutations/deletions of the WT1 gene, loss of heterozygosity on chromosome arms 11p and 11q, chromosome ploidy and histology in Wilms' tumors in Japan

Incidence rates of Wilms' tumor (WT) markedly differ in East Asian and Caucasian children. In the present study, we examined WT1 deletions/mutations and loss of heterozygosity (LOH) on 11p and 11q in a large number of WTs and compared our findings with those from 4 series of Caucasian WTs. Incidence rates of the subtle WT1 mutation in 3 of the 5 series of sporadic and unilateral WTs including ours were 4.3-6.2% and similar. However, gross homozygous WT1 deletion was more frequent in our series than in some others. In addition, our series tended to show a higher incidence of LOH limited to 11p13 and a lower incidence of LOH including 11p15 than the Caucasian one. These findings indicate some genetic differences in WT between the 2 regions. One of the 4 Caucasian series reported a correlation of germinal WT1 mutation with the predominantly stromal histology. The present study not only confirms the correlation of germinal WT1 deletion/mutation with predominant stromal histology but also establishes a correlation with somatic WT1 deletion/mutations with predominant stromal histology. While WTs with WT1 abnormalities usually showed pseudodiploidy and predominant stromal histology, those without WT1 abnormalities showed various chromosome numbers and histologic subtypes.

Correlation of chromosome abnormalities with presence or absence of WT1 deletions/mutations in Wilms tumor

Of 40 Wilms tumors with chromosome abnormalities, 6 were hypodiploid, 10 were pseudodiploid, 7 were hyperdiploid with 47 to 49 chromosomes, and 17 were hyperdiploid with 50 or more chromosomes, mostly including +12. WT1 deletions/mutations were found in one hypodiploid, eight pseudodiploid, and one hyperdiploid (47-49 chromosomes) tumor, but in none of the hyperdiploid (> or =50 chromosomes) tumors. Of the 10 tumors with WT1 abnormalities, 6 had a homozygous WT1 deletion, 1 had a nonsense WT1 mutation and loss of heterozygosity at 11p, 1 had an intragenic hemizygous WT1 deletion without detectable WT1 mutation, and 2, which occurred in Wilms tumor-aniridia-genitourinary abnormalities-mental retardation syndrome patients, had a hemizygous deletion and a missense or frameshift mutation of WT1. Six of the nine tumors with homozygous or hemizygous WT1 deletions had chromosome aberrations involving chromosome band 11p13 in one of the two chromosomes 11. While one hypodiploid and one pseudodiploid patient died of the disease, and one hyperdiploid (47-49 chromosomes) patient was alive in nonremission, all hyperdiploid (> or =50 chromosomes) patients had no evidence of disease at the last follow-up. Our data show that chromosome aberrations are closely correlated to WT1 abnormalities and suggest that hyperdiploid (> or =50 chromosomes) Wilms tumors may be characterized by the absence of WT1 abnormalities and possibly also by a favorable prognosis.

A common region of loss of heterozygosity in Wilms' tumor and embryonal rhabdomyosarcoma distal to the D11S988 locus on chromosome 11p15.5

The development of Wilms' tumor has been associated with two genetic loci on chromosome 11: WT1 in 11p13 and WT2 in 11p15.5. Here, we have used loss of heterozygosity (LOH) in Wilms' tumors to narrow the WT2 locus distal to the D11S988 locus. A similar region was apparent for the clinically associated tumor, embryonal rhabdomyosarcoma. We have also demonstrated that a constitutional chromosome translocation breakpoint associated with Beckwith-Wiedemann syndrome and an acquired somatic chromosome translocation breakpoint in a rhabdoid tumor each occur in the same chromosomal interval as the smallest region of LOH in Wilms' tumors and embryonal rhabdomyosarcoma. Finally, we report the first Wilms' tumor without a cytogenetic deletion that shows targeted LOH for 11p15 and 11p13 while maintaining germline status for 11p14.