
[Cancer Research 60, 6623-6629, December 1, 2000]
© 2000 American Association for Cancer Research
Allelic Deletions of Cell Growth Regulators during Progression of Bladder Cancer1
Hanne Primdahl,
Hans von der Maase,
Mariann Christensen,
Hans Wolf and
Torben F. Ørntoft2
Molecular Diagnostic Laboratory, Departments of Clinical Biochemistry [H. P., M. C., T. F. Ø.] and Urology [H. W.], Aarhus University Hospital, 8200 Aarhus N, and Department of Oncology, Aarhus University Hospital, 8000 Aarhus C [H. v. d. M.], Denmark
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ABSTRACT
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Cell growth regulators include proteins of the p53 pathway encoded by
the genes CDKN2A (p16, p14arf), MDM2,
TP53, and CDKN1A (p21) as well as proteins
encoded by genes like RB1, E2F, and MYCL.
In the present study we investigated allelic deletions of all these
genes in each recurrent bladder tumor from well-defined clinical
material with more than 3 years of follow-up. We followed three groups
(22 or 23 patients/group) of patients with: (a)
recurrent noninvasive tumors (Ta); (b) primary
muscle-invasive tumors (T2T4); and (c) progressing
tumors (Ta/T1
T2/T4). We found a significant difference in the
numbers of gene loci hit by deletions in muscle-invasive
versus noninvasive tumors (P = 0.0000002), with the genes most often hit by deletions in
muscle-invasive tumors being TP53, RB1, and
MYCL. A number of novel findings were made. Losses of
MYCL and RB1 alleles were more pronounced
in patients having concomitant field disease because 11 of 14
informative cases showed losses compared with 3 of 8 cases without
field disease. A more pronounced deletion of TP53
(P = 0.002) and RB1
(P = 0.02) was found in the progressing
tumor group compared with the recurrent noninvasive group, and,
finally, the combined loss of TP53 and
RB1 was present only in the progressing tumor or
muscle-invasive groups. Deletion of two or more loci in TP53,
MYCL, RB1, and CDKN2A was found
in 10 patients in the progressing tumor group and in only 1 patient in
the recurrent noninvasive group (P = 0.004). The data demonstrate that a characteristic difference between
recurrent noninvasive and recurrent progressing bladder tumors is loss
of cell cycle-regulatory genes in the latter group.
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INTRODUCTION
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One of the most important features of urothelial cancers of the
bladder and upper urinary tract is metachronous or synchronous
multifocal occurrence with high frequency. Between 70% and 80% of
patients with bladder cancer have only noninvasive disease (Ta) or
tumors with invasion no deeper than the lamina propria (T1) on initial
presentation, and the remainder have muscle-infiltrating or deeper
cancers (T2-T4) (1)
. The risk of developing a
muscle-invasive disease is only 10% in a patient with a noninvasive
bladder tumor (Ta), whereas the majority of patients diagnosed with
concomitant carcinoma in situ (flat lesion grade 34) will
develop a muscle-invasive tumor. At present, one cannot predict which
patient with a noninvasive tumor will experience progression to
invasive disease and which one will not. The search for predictive
markers has been the aim of many studies and has included, among
others, studies of nuclear volume (2)
, blood group
antigens (3
, 4)
, adhesion potential (5
, 6)
,
epidermal growth factor receptors, (7)
and matrix
metalloproteinases (8)
. However, these markers have only
shown a general relation to prognosis and provide no definitive
information for the specific patient. In recent years, a large body of
information has been accumulated on the growth-regulatory pathway
through which the p53 and Rb proteins are working, including proteins
encoded by genes like MDM2, CDKN1A (p21),
CDKN2A(p16, p14arf), RB1, E2F, and
MYCL (Fig. 1)
. In the present study, we investigated allelic losses of these genes
as predictors of disease course. Alterations of the TP53
gene seem to be of importance in most cancers. It is known that
LOH3
of the TP53 gene is correlated to high grade and stage of
bladder tumors (9
, 10)
, and LOH of 17p (the
TP53 locus) is associated with an invasive phenotype
(11)
. Furthermore, positive immunostaining for p53 protein
correlates with disease progression (12)
. Other components
of the p53 and Rb pathways have also been investigated in bladder
cancers, including MDM2 (13
, 14)
, p21
(15
, 16)
CDKN2A (17)
,
E2F (18)
, and RB1 (19
, 20)
. Despite the many studies of these components in bladder
cancer (9
, 10
, 17
, 21
, 22)
, very few, if any, have
analyzed the various components of this pathway in single individual
tumors to verify the number of different alterations. This could be of
importance because losses of some gene products may promote cancer,
whereas others may inhibit it. Furthermore, alterations of
specific genes should be interpreted in the context of the presence or
absence of downstream effector proteins. Based on this, we examined all
of the shown growth regulators (Fig. 1)
related to the p53 and Rb
pathways in each tumor from three groups of patients: (a)
patients with primary muscle-invasive tumors; (b) patients
with recurrent noninvasive tumors; and (c) patients with
progressing tumors. A number of novel findings relating allelic
deletions to clinicopathological data were made. We detected a
significant difference in the numbers of cell growth-regulatory gene
loci affected by allelic deletions in low-stage versus
high-stage tumors, frequent deletions at the MYCL locus, a
difference in the pattern of allelic deletions in high-stage tumors
with and without field disease, a more pronounced deletion of
TP53 and RB1 in the progressing tumor group, and
the presence of combined deletions of TP53 and
RB1 only in the progressing tumor or muscle-invasive groups.

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Fig. 1. Cell growth-regulatory pathways examined in this study.
The action of the p53 protein is stimulated by any kind of genotoxic
stress. An increased level of active p53 protein stimulates p21 to stop
activation of cyclin-dependent kinases, phosphorylation of rb1, and
release of e2f, which leads to S-phase progression. p16 is an
inhibitor of cyclin-dependent kinases, leading to decreased release of
e2f and cell cycle arrest. p14 binds to mdm2 and stabilizes p53.
MYCL is a proto-oncogene encoding a protein that, among
other actions, inhibits p21, leading to decreased inhibition of e2f
release and thus S-phase progression. This model of cell growth
regulation is simplified, and new knowledge of genes involved is still
being acquired. Revised from Ref. 32
.
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MATERIALS AND METHODS
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Patients.
Three groups of patients were selected from a clinical data and tissue
bank from approximately 1000 patients followed for more than 3 years on
average. The noninvasive group consisted of 23 patients (18 males and 5
females; median age, 73 years; age range, 4283 years) who had at
least three metachronous stage Ta tumors and did not have a tumor of
higher stage during a median follow-up of 205 weeks (range, 72218
weeks). The muscle-invasive tumor group consisted of 22 patients (20
males and 2 females; median age, 67 years; age range, 4684 years) who
had a stage T2 or higher stage tumor as their first bladder tumor ever.
The progressing group consisted of 23 patients (17 males and 6 females;
median age, 71 years; age range, 5083 years) who had a stage Ta or T1
tumor as their first tumor and whose disease later progressed to a
higher stage. We included both Ta and T1 to get a reasonable
number of tumors. From each patient, tumor tissue and blood were
collected if informed consent was obtained.
Material.
Tumors were obtained fresh from surgery, frozen immediately, and stored
at -80°C. DNA was extracted from tumor tissue and blood by using a
Puregene DNA extraction kit (Gentra Systems, Minneapolis, MN) following
the manufacturers instructions. Because of possible normal tissue
contamination, all invasive tumors without evident allelic losses were
reanalyzed using microdissected tumor tissue. Microdissection was
performed using x100 magnification in a microscope and
410-µm-thick serial sections of paraffin-embedded tumors.
Microdissected tumor areas were deparaffinized by heating to 70°C,
followed by rinsing in Xylol. DNA was extracted as described above.
LOH Detection.
DNA from tumor and blood was analyzed for allelic deletions and MIN by
using microsatellite markers. Microsatellites were chosen near
growth-regulatory genes using information from the National Center for
Biotechnology Information database Genemap 98 or based on published
data (23
, 24)
. Sequences of the primers used are listed in
Table 1
. Fluorescence-labeled primers were purchased from Hobolt DNA Synthesis
(Hilleroed, Denmark) and DNA Technology (Aarhus, Denmark).
PCR Amplification.
PCR reactions were carried out in a 19-µl volume containing 100200
ng of purified genomic DNA; 2 pmol of each primer; 50 mM
KCl; 10 mM Tris (pH 9.0); 1.5 mM
MgCl2; dATP, dTTP, dCTP, and dGTP (132
mM each); and 0.5 unit of Taq DNA polymerase. The reaction
mixture was subjected to 5 min of denaturing at 95°C and 3040
cycles of 95°C for 0.51.5 min, 50°C63°C for 45 s to 1.5
min, and 72°C for 1.5 min. The final cycle was followed by a step at
72°C for 5 min. PCR conditions were optimized according to the
sequence of the primers, and PCR was carried out in a MJ Research
Thermocycler (PTC 200/PTC 225).
Electrophoresis.
PCR products were analyzed by electrophoresis on 4.75%
polyacrylamide/6 M urea denaturing gels using an ABI Prism
377 DNA sequencer and Genescan software (3 h, 51°C, 2.96 V).
Interpretation of Data and Definition of Terminology.
MIN was defined as the presence of significant new bands, following PCR
amplification of tumor DNA, that were not present in corresponding
normal DNA. Tumors with MIN were excluded from allelic deletion
examination. Allelic deletion was defined as loss of a significant part
of one allele in tumor DNA compared with the corresponding normal DNA.
This was determined by comparing the area under the curve for the two
alleles from tumor and normal DNA in the curves obtained from the
Genescan program. To determine the between-run variation, we repeated
the entire procedure on 10 samples of corresponding tumor and normal
DNA for the first six primer sets. We normalized the areas by
dividing the ratio between tumor alleles with the ratio between normal
alleles [(tumor allele 1:tumor allele 2)/(blood allele 1:blood allele
2)]. Based on these data, the variation of each amplicon was defined,
and a significant loss was defined as a difference of more than 3 SDs
between the allelic ratio in tumor and the allelic ratio in blood.
Determinations of area under the curve in the first six primer sets
were compared with a visual scoring by two independent observers and
showed a high degree of correlation (93%). Therefore, we decided to
use visual scoring by two independent and experienced observers on the
rest of the amplicons. All cases with allelic deletions or MIN in
primary analysis were confirmed by repetition of the complete assay and
rescoring.
To analyze the importance of the number of genomic deletions in a
single tumor, we divided the material into tumors having only one or no
deletion, (low frequency) and tumors having two or more deletions (high
frequency).
Statistics.
Two different tests were used. For samples larger than 50 and figures
expected to be larger than 5, we used the
2
test. For smaller samples and figures, we used the two-sided Fishers
exact test. When one locus was analyzed with more than one primer, the
combined result was counted as one event.
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RESULTS
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The deletion of alleles was examined at the following loci in each
tumor: TP53 (two markers); MDM2; CDKN1A(p21); MYCL; CDKN2A (p16 and p14arf);
RB1; and E2F (Fig. 2)
. A pronounced difference in the frequency of allelic deletion was
found between the noninvasive group of tumors and the muscle-invasive
group of tumors. Seven of the 23 noninvasive tumors showed deletion of
at least one locus compared with 19 of 22 muscle-invasive tumors (Table 2)
. In the muscle-invasive tumors, an average of 1.6 loci were deleted
compared with 0.3 loci in the tumors of the noninvasive group
(P = 0.0000002,
2
test). If a value of
2 deletions was used to define tumors with
frequent deletions, then the number of tumors with frequent deletions
amounted to 11 of 22 muscle-invasive tumors and only 1 of 23
noninvasive tumors (P = 0.001; two-sided
Fishers exact test; Table 2
) because tumor 4 from patient 60 was the
only one that lost both a TP53 and an E2F allele
in the latter group. It was remarkable, however, that half of the
muscle-invasive tumors had only one deletion (eight tumors) or no
deletions (three tumors; Table 2
).

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Fig. 2. Examples of electropherograms of microsatellites from
tumors and corresponding blood. Each vertical row
represents normal and tumor DNA from metachronous tumors in the same
patient. A, gene locus RB1 in patient 157; both alleles
are retained in all three tumors. B, gene locus
RB1 in patient 172; allelic deletion occurs in all three
tumors. C, patient 679; allelic deletion of
CDKN2A (p16) is seen in tumor 1 (first
row), and allelic deletion of MYCL is seen in
tumor 3 (second row). D, gene locus
TP53 in patient 157; allelic deletion is seen in the
tumor.
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Table 2 Clinical and genetic profiles for noninvasive and muscle-invasive
tumors
PT, patient number; VISIT, visit number in mob project; FIELD, whether
or not the patient had corresponding field disease; CIS, carcinoma
in situ; FD, frequency of deletions. High (H) if two or more
loci showed deletions; Low (L) if zero or one loci showed
deletion.
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In the muscle-invasive tumors, different combinations of deletions were
detected from deletion of one RB1 allele to deletion of
TP53, CDKN1A, CDKN2A, and
RB1 alleles in a single tumor. The RB1 and
MYCL loci showed significantly more deletions in
muscle-invasive tumors than in noninvasive ones [RB1,
P = 0.001; MYCL,
P = 0.003 (two-sided Fishers exact test)].
CDKN2A, which is located at chromosome 9p, was deleted with
a similar frequency in noninvasive (3 of 13 tumors) and muscle-invasive
(6 of 17 tumors) tumors, as expected.
The muscle-invasive tumors could be separated into two groups with or
without concomitant carcinoma in situ. The patients with
concomitant lesions have a field disease with grade 2 dysplasia or
carcinoma in situ/invasive carcinoma in selected site
biopsies. As a novel finding, we observed that the deletions of
MYCL and RB1 alleles were more pronounced in
patients having field disease because 11 of 14 informative cases showed
deletions compared with 2 of 8 cases without field disease
(P = 0.04, two-sided Fischers exact test).
All tumors with more than two deletions had concomitant field disease
(Table 2
; Fig. 3
).

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Fig. 3. Percentage of tumors within each patient group showing
allelic deletion of two or more of four genes (TP53,
RB1, MYCL, and CDKN2A).
Ta progressing and T1 progressing
represent the last tumor of that stage before progression.
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Because of the significant difference between the noninvasive and
muscle-invasive tumors, we decided to examine losses of
TP53, CDKN2A, MYCL, and RB1
in a group of patients with progressing tumors and in patients with
recurrent noninvasive tumors (Table 3)
. As a novel finding, we demonstrate that the number of patients with
allelic deletions of RB1 in any tumor was significantly
higher in the progressing group (7 out of 21 informative cases) than in
the recurrent Ta group (0 out of 17 informative cases;
P = 0.02, two-sided Fishers exact test).
For the TP53 locus, 12 of 17 versus 3 of 19
informative patients had deletions (P = 0.002, two-sided Fishers exact test). We compared all Ta tumors later
developing into invasive tumors with tumors from patients with
recurrent Ta tumors and found allelic deletion of RB1 in 2
of 11 tumors in the progressing group versus 0 of 43
tumors in the recurrent noninvasive group
(P = 0.076, two-sided Fishers exact test).
For TP53, the numbers were 4 of 9 versus 4 of 46
(P = 0.037, two-sided Fishers exact test).
The most striking difference was that RB1 never showed
deletions in the group with recurrent noninvasive tumors. The
CDKN2A locus and MYCL were deleted to the same
extent in both groups. The deletions of RB1 were present
from the beginning of the progressive disease course in all but one
case, as was TP53 except in three cases. Deletions of
alleles at these two loci could be important predictors for the disease
course. Deletions were not detected at all visits in some cases (Table 3)
. This might indicate different tumor cell populations. As shown by
case 679 in the recurrent noninvasive group, different populations of
tumor cells seemed to be present because the CDKN2A locus
showed deletion in tumor 1 and a normal pattern in tumor 3, whereas the
MYCL gene locus showed the opposite pattern (Fig. 2C)
. Seven of the 23 patients that showed progression had no
deletions at all of the examined loci. Intervals between recurrences
were similar in the two groups. An average of 236 days passed between
the recurrence of noninvasive tumors in the group that did not
progress, and an average of 217 days passed from the last Ta or T1
tumor to the first tumor of a higher stage in the progressing group.
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Table 3 Clinical and genetic profiles for tumors from patients with progressing
and recurrent noninvasive tumors
The table only shows selected tumors from each patient based on
availability of tissue and the absence of urinary tract infection.
Furthermore, a selection of last noninvasive, first invasive for
progressing group was used. PT, patient number; VISIT, visit number;
FD, frequency of deletions. High (H) if two or more out of four loci
showed deletions. Low (L) if zero or one loci showed
deletion.
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If we define the simultaneous deletion of two or more gene loci in
TP53, MYCL, RB1, and CDKN2A
as a high frequency of deletions, then 10 patients showed a high
frequency of deletion in the progressing group, and only 1 patient
showed such a high frequency in the recurrent noninvasive group. The
number of tumors with a high frequency of deletion differed markedly
between the groups examined (Fig. 3)
but was always 50% or less of
examined tumors.
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DISCUSSION
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We have studied the allelic deletion of genes involved in cell
cycle regulation in a well-characterized clinical material consisting
of bladder cancer patients with stable or progressing tumors. We found
a significantly higher frequency of allelic deletions in high-stage
versus low-stage tumors and, as a novel finding, in
progressing versus recurrent noninvasive disease. The genes
most often affected by allelic deletions in muscle-invasive tumors were
TP53, RB1 and, as a novel finding,
MYCL. Dichotomizing the patients into those with tumors
having a high frequency of deletions (two or more deletions) and those
with a low frequency of deletions showed, for the first time, a
remarkable overrepresentation of high-frequency deletions in
progressing tumors. Although allelic deletions were frequent in certain
patient groups, some patients in each group showed a complete absence
of deletions, indicating that the muscle-invasive or progressing tumors
might consist of two different groups, one with allelic deletions and
one with other characteristics.
The higher frequency of allelic deletions in muscle-invasive tumors
corresponds well with the findings by other authors that mutations,
allelic loss, and abnormal expression of the p53 protein are more
pronounced in high-stage tumors than in low-stage tumors (9
, 10
, 12)
. Allelic loss was found mainly in RB1,
MYCL, CDKN2A, and TP53 and was rare
for the genes MDM2 and E2F.
mdm2 up-regulation is expected to be unfavorable because the
protein abrogates the growth suppression function of p53. In human
breast cancer, mdm2 overexpression was seen in 24 of 33 cases
(25)
. In bladder cancer, a positive correlation between
p53 accumulation and mdm2 overexpression was shown, but mdm2
overexpression alone had no prognostic significance (13)
.
The CDKN2A gene encodes cell cycle-regulatory proteins p16
and p14arf, which share one exon with different reading frames. Both
are tumor inhibitors; p14 binds to mdm2 and inhibits p53 degradation,
and p16 binds to cyclin-dependent kinase 4 (Fig. 1
; Ref.
26
). A microsatellite at the IFNA locus is commonly
used to investigate the CDKN2A locus (27
, 28)
; however,
deletions may occur that affect only the CDKN2A gene and not
IFNA. Based on this, our findings concerning CDKN2A may underestimate
the frequency of deletions of the CDKN2A gene. The tumor
inhibitor p21, like p16, works through inhibition of cyclin-dependent
kinases, abrogating the phosphorylation of rb1 and arresting the cell
cycle at the G1 checkpoint. The
CDKN1A gene is directly transcribed by p53 and is related to
morphological indicators of cell proliferation. Its relation to
prognosis in bladder cancer is ambiguous (15
, 16)
. In a
previous publication (17)
, the CDKN2A gene was
deleted in 13 of 140 bladder tumors, all of which had small defined
deletions at 9p21.
The E2F gene product is a transcription factor that promotes
G1 progression. Loss or inactivation of this
protein could, in theory, arrest the cell cycle, but in a recent
publication (18)
, lack of the e2f protein was related to
disease progression, and e2f inactivation may be related to replication
errors (29)
. The rb1 protein binds to e2f and thus causes
cell cycle arrest. Individuals with germ-line mutations in the
RB1 gene are at high risk of developing retinoblastoma and
other cancers (30)
. Altered expression of rb1 is
associated with invasive bladder tumors (31)
and bladder
cancer recurrence (19)
, and the alteration of p53 and rb1
in the same tumor is associated with tumor progression
(20)
. The role of MYCL is difficult to
interpret. The MYCL gene is a proto-oncogene. Among other
mechanisms, it might work through inhibiting the p21-mediated
inhibition of rb1 phosphorylation (32)
. Another member of
the myc family, C-MYC, plays a role in p53-dependent apoptosis
(33)
. The role of MYCL is less clear because it
accelerates apoptosis after interleukin 3 withdrawal, whereas
overexpression produces resistance to cytotoxic drugs
(34)
. We found one previous publication (35)
on MYCL and bladder cancer in which the authors concluded
that the MYCL genotype was not a prognostic factor in
bladder cancer. In our material, allelic deletion of MYCL
was associated with high-stage tumors, possibly indicating a growth
advantage for cells with only one MYCL allele.
Lack of p53 protein is supposed to lead to increased cell division
because the CDKN1A gene will not be encoding p21 protein,
and there will be increased action of cyclin-dependent kinases and
release of e2f, leading to S-phase progression and possible tumor
growth. This will be enhanced by the lack of p16 protein, which
is needed to stop the cyclin-dependent kinase-dependent phosphorylation
of rb1 and release of e2f. As a result, loss of TP53,
CDKN1A, CDKN2A, and RB1 may give the
cell a growth advantage, whereas loss of E2F and
MDM2 may stop S-phase progression and possible tumor growth
(32)
. It was characteristic in our material that
E2F and MDM2 were rarely hit by deletions
compared with the other genes, indicating that almost only unfavorable
deletions leading to increased S-phase progression were present.
However, if the deletions we observed have any biological importance,
they should influence the amount or quality of the gene products. This
could be due to either a gene dose effect or inactivation of the
remaining allele by a mutation or by methylation of CpG islands in the
promoter region. The latter is a known mechanism that reduces the
transcription of genes (36)
. There are some possibilities
for underscoring deletions. We tried to rule out normal tissue
contamination by microdissecting paraffin-embedded tissue in
muscle-invasive tumors that showed no deletions when frozen
tumor tissue was examined. Another possibility is too much template.
Because almost all tumors showed some degree of deletion, it seems that
saturation of the PCR process is no problem. Other authors have used
5300 ng of template (37
, 38)
. We conclude that allelic
deletions of genes involved in cell growth regulation are of importance
in the progression of bladder cancer. We detected a pronounced
difference in the frequencies of deletions in noninvasive
versus muscle-invasive tumors. If we define the simultaneous
loss of two or more gene loci in TP53, MYCL,
RB1, and CDKN2A as a high frequency of deletions,
then 11 of 23 muscle-invasive tumors and only 1 of 23 noninvasive
tumors showed this pattern. A striking new finding was that 10 patients
in the progressing group and only 1 patient in the recurrent
noninvasive group showed a high frequency of deletions. The
differences were more pronounced for RB1, MYCL,
and TP53. The number of tumors showing a high frequency of
deletions was markedly different between the groups examined but was
always 50% or less of examined tumors. Based on this, one might
suggest that two different pathways may lead to bladder tumor
progression, one in which deletion of alleles in cell cycle regulators
is common and one in which such deletions do not occur.
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ACKNOWLEDGMENTS
|
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We thank Ingelis Thorsen, Lotte Gernyx, and Bente Hein for
skillful technical assistance; Alexander Iovanowich for software
programming; and Flemming Brandt Sørensen for assistance with tissue
material.
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FOOTNOTES
|
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 Supported by grants from The Danish Cancer
Society, Karen Elise Jensens Fund, Aarhus County Research Fund,
Professor Jens C. Christoffersens Mindefond, Radiumstationens
Forskningsfond, and Max and Inger Worzners Mindelegat. 
2 To whom requests for reprints should be
addressed, at Department of Clinical Biochemistry, Skejby Sygehus,
Brendstrupgaardsvej, 8200 Aarhus N, Denmark. Phone: 45-89-49-51-01;
Fax: 45-89-49-60-18; E-mail:orntoft{at}kba.sks.au.dk 
3 The abbreviations used are: LOH, loss of
heterozygosity; MIN, microsatellite instability. 
Received 1/10/00.
Accepted 9/27/00.
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