(American Journal of Pathology. 2001;158:393-398.)
© 2001 American Society for Investigative Pathology
Gain of 1q Is Associated with Adverse Outcome in Favorable Histology Wilms Tumors
Sandra Hing*,
Yong-Jie Lu*
,
Brenda Summersgill
,
Linda King-Underwood*,
James Nicholson
,
Paul Grundy§,
Richard Grundy
,
Manfred Gessler||,
Janet Shipley
and
Kathy Pritchard-Jones*
From the Sections of Paediatrics *
and Molecular
Carcinogenesis,
Institute of Cancer
Research/Royal Marsden Hospital NHS Trust, Sutton, Surrey,
United Kingdom; the Addenbrookes Hospital,
Cambridge, United Kingdom; the Birmingham Childrens
Hospital,
Birmingham, United Kingdom; the
Molecular Oncology Program,§
Cross Cancer
Institute, Edmonton, Alberta, Canada; and the Theodor-Boveri-Institut
für Biowissenschaften,||
(Biozentrum) der
Universität Würzburg, Germany
 |
Abstract
|
|---|
Although several genes/genetic loci involved in the etiology of
Wilms tumor have been identified, little is known of the
molecular changes associated with relapse. We therefore undertook an
analysis by comparative genomic hybridization (CGH) of 58 tumor samples
of favorable histology Wilms tumor taken at initial diagnosis and/or
relapse. Tumors with anaplastic histology were excluded as this is
known to be associated with p53 mutation and a poor
prognosis. A control group of 21 Wilms tumors that did not relapse
was also analyzed. The overall frequency of gains or losses of genetic
material detected by CGH was similar in both groups (77% in relapsing
tumors and 70% in the nonrelapse group) as was the median number of
changes per tumor (relapse group: n = 4,
range, 1 to 19; nonrelapse group: n =
3, range, 1 to 8). However, gain of 1q was
significantly more frequent in the relapse series [27 of 46 (59%)
versus 5 of 21 (24%), P =
0.019]. In 12 matched tumor pairs, the CGH profiles,
including 1q gain, were similar at diagnosis and
relapse, with little evidence for further copy number changes
being involved in clonal evolution. The results suggest that 1q gain at
diagnosis could be used to identify patients with favorable histology
Wilms tumor at increased risk of relapse who might benefit from early
treatment intensification.
 |
Introduction
|
|---|
Wilms tumor or nephroblastoma, is
one of the success stories of pediatric oncology, with overall
long-term survival rates in excess of 85%. However, there remains a
small group of patients whose tumors progress or relapse unexpectedly.
In these cases, the chance of successful retreatment is much poorer,
despite intensive second line therapy.1
Furthermore,
survivors risk compromised long-term renal function through use of
potentially nephrotoxic chemotherapeutic agents administered to a
uninephric patient. Therefore, selection of patients at diagnosis who
might benefit from intensification of initial chemotherapy is
important. The prognostic factors used currently by the two major
international Wilms tumor groups for risk-adapted stratification of
therapy are tumor stage and histological subtype. Unfavorable histology
Wilms tumor is defined by the presence of anaplasia, which can be
focal or diffuse, the latter subtype having survival rates of <50%.
Anaplasia is associated with somatic p53 mutation that can
be confined to areas of focal anaplasia, implying its involvement in
clonal evolution.2
However, the majority of Wilms tumors
that relapse do not show anaplasia, implying that other factors must be
involved in treatment failure.
Several genes are known to be involved in Wilms tumor development,
including the WT1 gene at 11p13, one or more genes at the
Beckwith-Wiedemann syndrome locus at 11p15, at least two familial
Wilms tumor genes at 17q and 19q, plus other loci defined by allele
loss and/or rare translocation breakpoints.3-6
WT1 is mutated in
10% of sporadic Wilms tumors, where
its prognostic significance is not defined, although WT1
mutation has been associated with a poor outcome in acute myeloid
leukemia.7
Extensive allele loss studies have suggested
that loss of heterozygosity (LOH) for 1p, 16q, and possibly 22q are
adverse prognostic features in Wilms tumor.8-10
These
are now being tested prospectively in the current National Wilms
Tumor Study Group trial, NWTS-5. Expression of the multidrug resistance
gene, MDR1, is not common in Wilms tumor.11
More
recently, other molecular factors such as expression of p53 and high
levels of telomerase activity have been associated with increased risk
of relapse in Wilms tumor.12,13
In this study, we have
screened for genomic imbalances using comparative genomic hybridization
(CGH) in favorable histology Wilms tumors that relapsed and compared
the results with cases that did not.
 |
Materials and Methods
|
|---|
Tumors that were snap-frozen after surgery were received from the
National Wilms Tumor Study Group, various United Kingdom Childrens
Cancer Study Group centers, and Germany. There were 58 relapsed Wilms
tumors (12 matched tumor pairs sampled at diagnosis and at relapse, 29
at diagnosis only, and five at relapse only). A nonrelapse control
group consisting of 21 Wilms tumors from patients with a minimum of 2
years of follow-up without relapse was also analyzed, with observer
blinding to clinical outcome data. The distribution of tumor stage in
the two groups is shown in Table 1
.
Tumors with anaplastic histology were deliberately excluded, as these
are associated with p53 mutations and seem to be a distinct
biological entity.
CGH was performed as described previously.14
Briefly, 1
µg of both tumor and sex-matched reference (from healthy normal
individuals) DNA was directly labeled by nick translation with either
fluorescein-12-dUTP or rhodamine-12-dUTP (fluorored or fluorogreen;
Amersham International, Amersham, Buckinghamshire, UK). Labeled DNA was
assessed on a 1% agarose gel with an optimal size of 500 to 2,000 bp.
Between 500 to 750 ng of each DNA and 25 to 40 µg of Cot 1 DNA (Life
Technologies, Inc., Rockville, MD) was co-hybridized to normal
denatured metaphase slides (Vysis Inc., Downers Grove, IL) for 72
hours at 37°C. After hybridization the slides were washed and mounted
in Citifluor antifade (Vector Laboratories Inc., Burlingame, CA) with
0.1 µg/ml 4',6-diamidino-2-phenylindole as a counterstain. Images
were captured using a cooled charge-coupled device camera
(Photometrics, Tuscon, AZ) and the QUIPS-CGH software package (Vysis
Inc.) was used for analysis. The prevalences of chromosomal imbalances
between the relapse and nonrelapse groups were compared by the
two-tailed Fishers exact test.
 |
Results
|
|---|
At least five representative metaphases were combined to produce a
mean fluorescence ratio ±1 SD. The average ratios of fluorescence
intensity and their SDs were determined in control CGH experiments
using differentially labeled normal DNA and did not exceed 1.0 ±
0.15. A copy number change in a sample was indicated when the average
fluorescence ratio from at least 10 chromosomes lay outside this range
(0.85 to 1.15). High copy number gain was scored when the average
ratios at a chromosomal location exceeded 1.5.
Overall, CGH analysis revealed genomic copy number changes in >70% of
Wilms tumors in both the relapse and nonrelapse groups, with gains
being more frequently observed than losses (Figures 1, 2, and 3)
. Gain of 1q material was the most
frequently observed change in the relapse group and this was
significantly higher than the rate in the nonrelapse group [27 of 46
(59%) versus five of 21 (24%), P = 0.019,
Fishers exact test]. Most of those tumors showed gain of the whole
of chromosome 1q, but in six tumors the gain was partial and allowed
definition of a smallest region of common gain spanning 1q21-25. In
three cases, 1q gain was the sole CGH abnormality, including one case
analyzed at diagnosis, one at relapse, and a matched pair. In eight
cases, 1p loss coexisted with 1q gain, suggesting the existence of an
isochromosome 1q or an unbalanced translocation. Other consistent
changes, all found in one third or less of cases, included gains of
material from chromosomes 8 and 12 and loss involving 1p, 11p, 16q, and
22q. These changes occurred at similar frequencies in both groups and
were not significantly associated with adverse outcome (Table 2)
. For the majority of imbalances, the
average fluorescence ratios were just outside the cut-off limits. This
would be consistent with cellular heterogeneity of copy number changes
within tumors.

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Figure 1. Ideogram representing 34 relapsing Wilms tumors taken at diagnosis or
relapse. Solid gray lines on the right represent
gain at diagnosis and hashed lines represent gain at
relapse. Solid black lines on the left represent
loss at diagnosis and hashed lines represent loss at
relapse. Thick solid or hashed lines represent
higher levels of gain (fluorescence ratio
>1.5). Case numbers are shown at the top of
each vertical line.
|
|
Gain of material on 1q was associated with more advanced disease at
first diagnosis: 70% of tumors with 1q gain were stage III or IV at
diagnosis compared with only 43% of tumors lacking 1q gain
(P = 0.05) (Table 1)
.
CGH analysis of 12 paired tumor samples from both diagnosis and relapse
did not reveal any evidence for clonal evolution (Figure 2)
. Eleven of
the 12 matched tumor pairs had abnormalities detected by CGH; the
median number of changes was identical at diagnosis (median, 5; range,
2 to 19) and relapse (median, 5; range, 2 to 17). Regions of gain and
loss observed at diagnosis were generally still present at relapse with
occasional additional changes. Nine cases had gain of 1q and this was
detectable at diagnosis in all but one case. The tumor lacking CGH
changes had an identical WT1 mutation detectable in
both diagnosis and relapse specimens (homozygous nonsense mutation,
TCG
TAG = Ser313
STOP).
 |
Discussion
|
|---|
This is the first CGH study to focus on relapsed Wilms tumor and
demonstrates a significant association between gain of 1q genomic
material detected at original diagnosis and risk of tumor recurrence,
with a 4.5-fold increase in the relative risk of relapse. The region of
common gain is large, spanning 1q21-q25. This region has also been
associated with resistant disease in another childhood embryonal tumor,
neuroblastoma.15
Although gain of 1q is one of the
commonest changes observed in both adult and pediatric solid tumors,
this is usually as part of a spectrum of other changes.16
In three cases of Wilms tumor studied here, 1q gain was the sole
abnormality and it was the only genomic copy number alteration to show
a difference between relapsed and nonrelapsed cases. This suggests that
it may be possible to define a molecular marker at diagnosis to
identify a poorer risk group among favorable histology Wilms tumors
and ultimately to stratify treatment intensity.
Overall, this analysis shows a greater frequency but similar pattern of
chromosomal imbalances to previous CGH studies of Wilms tumors
sampled at diagnosis in which no clinical outcome data were
presented.17,18
These two previous analyses had found a
prevalence of only 21% and 40% CGH abnormalities, respectively, in
contrast to the >70% found in this study. The inclusion of a control
group of nonrelapsed tumors in the current analysis suggests that this
apparent difference is most likely because of differences of technique
sensitivity rather than patient selection. With the exception of the
excess of 1q gain, the pattern and frequency of abnormalities detected
by CGH in this series of relapsed Wilms tumors is similar to that
found cytogenetically in unselected tumors. A review of 142 Wilms
tumor karyotypes with clonal abnormalities revealed trisomy 8 and 12 in
20 to 25% of cases and gain of 1q in 20%. Chromosome loss was less
frequent, affecting mainly 11p (20% of cases).16
These
percentages are likely to be an overrepresentation of the true
prevalence of these changes, because Wilms tumors with normal
karyotypes were not included in the analysis, even though they
undoubtedly exist, as shown by both cytogenetic and CGH studies. The
mechanism for gain of 1q detected by CGH could reflect iso(1q)
formation or unbalanced translocation with 16q as the most frequent
partner.19,20
However, in the 27 cases with 1q gain, there
was corresponding loss of 1p in only seven cases and of 16q in only 10
cases. Taken together, these comparisons suggest that the association
of 1q gain with increased risk of tumor recurrence in favorable
histology Wilms tumor is a real one.
Previous allele loss studies of Wilms tumor have highlighted LOH at
16q, 22q, and possibly 1p as being associated with increased risk of
relapse.8-10
In those three studies, the prevalence of
allele loss at 16q (13 to 17%) and at 1p (10%) was similar to the
frequency of genomic loss detected by CGH in our study whereas that for
22q LOH (14%) was somewhat higher. However, there was no significant
association between CGH abnormalities at these loci and relapse (Table 2)
. This apparent discrepancy could either be because of allele
loss occurring together with reduplication, which would not be detected
by CGH, or to these regions of allele loss being associated with
anaplastic Wilms tumor, which was not included in our study.
Certainly, in only one study was the adverse effect of 16q LOH
independent of unfavorable histology and in another study, both 16q and
22q were associated with anaplasia.8,10
CGH abnormalities at the sites of other known or putative Wilms tumor
genes were not significantly associated with relapse (Table 2)
. Loss of
material from 11p, the site of the WT1 gene and the more
telomeric Beckwith-Wiedemann loci, was found at a much lower frequency
than the 30 to 50% of Wilms tumors reported to show allele loss.
This implies that 11p LOH commonly involves mitotic recombination or
loss and reduplication. The glypican 3 gene at Xp36 is mutated in the
Simpson-Golabi-Behmel syndrome of overgrowth and predisposition to
Wilms tumor.21
However, loss of the X chromosome was
seen in only seven tumors and was not associated with relapse.
Overall, this study of a large series of relapsed Wilms tumors
highlights only a single genomic region, namely gain of 1q21-25, as
being associated with tumor recurrence. This change is also associated
with more advanced disease at first diagnosis. Although the region of
gain detected here is large, it would span an amplicon at 1q21-22 found
commonly in sarcomas.22
It is also of interest that
regulatory sequences of an unknown putative target gene for WT1 map to
1q21-22.23
Of clinical relevance, we find no evidence for
instability of genomic copy number changes with tumor recurrence. This
suggests that whatever the molecular abnormality contained within the
1q gain, it is active from first presentation of the tumor. Further
analyses are underway to refine the common region of gain/amplification
and to identify overexpressed genes within this region. In this way, we
aim to identify a molecular marker(s) that may discriminate apoorer
risk group among favorable histology Wilms tumors and that
would be amenable to testing in a much larger series of Wilms tumors
in a prospective clinical trial.
 |
Acknowledgements
|
|---|
We thank the National Wilms Tumor Study Group, the Cooperative
Human Tissue Network (Columbus, OH), which is funded by the National
Cancer Institute, the German (GPOH) nephroblastoma study, and the
United Kingdom Childrens Cancer Study Group for access to specimens;
and Dr. I. Jeffrey (St Georges Hospital, London, UK), Dr. A. Kelsey
(Childrens Hospital, Manchester, UK), Dr. S. Variend (Childrens
Hospital, Sheffield, UK), and Dr. K. Brown (University of Bristol,
Bristol, UK); Roger Ahern (Royal Marsden Hospital Sutton,
Surrey), for statistical advice; and Miss Elizabeth Parr for
secretarial assistance.
 |
Footnotes
|
|---|
Address reprint requests to Dr. Kathy Pritchard-Jones, Section of Paediatric Oncology, Institute of Cancer Research/Royal Marsden, NHS Trust, Downs Rd., Sutton, Surrey SM2 5PT, UK. E-mail: kpj{at}icr.ac.uk
Supported by the Cancer Research Campaign (to K. P. J., L. K. U., and Y. J. U.), and the Childrens Cancer Unit Fund, Royal Marsden Hospital (to S. H.).
Accepted for publication October 6, 2000.
 |
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