Original articles
Hemizygous Deletions of Chromosome Band 16q24 in Wilms Tumor: Detection by Fluorescence In Situ Hybridization

https://doi.org/10.1016/S0165-4608(99)00093-XGet rights and content

Abstract

Loss of heterozygosity (LOH) for markers on chromosome arm 16q in Wilms tumor has been linked to an increased risk of treatment failure. We therefore postulated that fluorescence in situ hybridization (FISH) with probes from this region might enhance current strategies for identifying high-risk patients at diagnosis. In a blinded comparative pilot study of 19 Wilms tumor samples from 18 patients with favorable histology, FISH and DNA polymorphism analysis yielded concordant results in 14 cases, either retention (n = 6) or loss (n = 8) of chromosome arm 16q markers. Discordant findings in 4 of the 5 remaining cases resulted from detection of LOH, but no loss by FISH. Two of these cases, directly comparable at marker D16S422, appeared to have tumor-specific uniparental disomy, in that 2 copies of D16S422 and the 16 centromere were evident, despite LOH. In 2 other cases, the discrepancies could be explained by LOH confined to loci distal to the D16S422 locus. In the fifth case, FISH detected 2 distinct populations of tumor cells, one characterized by normal diploidy and the other by monosomy 16, whereas DNA polymorphism analysis failed to indicate LOH altogether. Thus, FISH confirmed the presence of allelic loss (hence, the possible location of biologically important tumor suppressor genes) on the distal long arm of chromosome 16 in cases of favorable-histology Wilms tumor, with the advantages of technical simplicity, successful analysis of samples that were otherwise uninformative by analysis of DNA polymorphisms, and the addition of internal controls for chromosomal aneusomy. We suggest that combined analysis of the chromosome 16q region in Wilms tumor by FISH and DNA polymorphism analysis would improve evaluations to identify high-risk patients who might benefit from alternative therapy.

Introduction

Wilms tumor, the most common renal malignancy of childhood, affects approximately 1 child per 10,000 worldwide under the age of 15 years [1]. Approximately 90% of patients with favorable-histology Wilms tumor will be cured by therapy based on disease stage and histologic findings [2]. Thus, it becomes important to identify at diagnosis patients in this subgroup who are at high risk of failure, so that they may receive more intensive therapy, while patients at lower risk continue to receive well-tolerated standard therapy, or are shifted to diminished treatment.

Loss of heterozygosity (LOH) for genetic markers on chromosome arms 16q and 1p in Wilms tumor appears to have prognostic significance. Grundy et al. [3], using DNA polymorphism analysis techniques (either restriction enzyme- or PCR-based), prospectively analyzed tumor tissue from 232 patients enrolled in recent trials of the National Wilms Tumor Study Group (NWTSG) for LOH of chromosomal segments involving chromosome arms 16q, 1p, and 11p. For the 35 patients whose tumors had LOH involving 16q, relapse-free survival and overall survival were 78% and 84%, respectively, at 2 years of follow-up, compared with 90% and 95% for patients whose tumors retained heterozygosity for loci in this region. Cases with LOH involving chromosome arm 16q had a 12-times greater death rate and 3-times greater relapse rate than did cases lacking this feature [3]. These differences remained statistically significant after correction for stage and histology. A similar trend was observed for LOH involving the short arm of chromosome 1; however, LOH for chromosome arm 11p was not associated with adverse overall or relapse-free survival.

Experience with other childhood tumors suggests that fluorescence in situ hybridization (FISH) might provide improved detection of high-risk cases of favorable-histology Wilms tumor. This method offers rapid detection of gene deletions and amplifications, chromosomal aneuploidy, and tumor-specific chromosomal translocations 5, 6, 7, 8, 9, 10, 11, 12, 13. Moreover, as a cytologic assay focusing on individual cells, it will distinguish between coexisting malignant subclones with evolving genetic abnormalities. In the present study, we collaborated with the NWTSG to compare FISH with DNA polymorphism analysis in the detection of prognostically important deletions of chromosome arm 16q. Our results suggest utility of adding FISH to current strategies of risk assessment in the management of Wilms tumor patients.

Section snippets

Tumor Specimens

Nineteen Wilms tumor samples from 18 patients (Table 1) were obtained from the Pediatric Oncology Group Tumor Bank (P. G.). All cases had favorable histology according to central pathology review by the NWTSG Pathology Center (J. B. B.).

DNA Probes

For FISH analysis, we isolated a P1 phage genomic clone (Genome Systems, St. Louis, MO, USA) that corresponds to the D16S422 locus, which maps to 16q24.2. Loci analyzed in our original LOH study included the more distal D16S7 and HP, which is more proximal [3].

Results and discussion

The demographics, stage, relapse status, and outcome of the cohort are shown in Table 1. Figure 1 shows the typical results of FISH analysis applied to all 18 primary Wilms tumor samples. The number of chromosomes 16 in each Wilms tumor interphase nucleus is indicated by a red hybridization signal, and the number of copies of D16S422 by a green hybridization signal. Tumor cells from four cases showed hemizygous deletions of D16S422, in that each cell contained a single hybridization signal for

Acknowledgements

This work was supported by Grant CA71907 and Cancer Center CORE Grant CA21765 from the National Cancer Institute, NIH, and by the American Lebanese Syrian Associated Charities (ALSAC), St. Jude Children's Research Hospital.

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