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Cancer Center, University of California, San Francisco, California 94143-0808 [S. S., D. H. M., D. G., T. G., J. B., B. P., D. P., C. Z., J. W. G.]; MD Anderson Cancer Center, Houston Texas [K. L., G. M.]; Duke University Medical Center, Durham, North Carolina 27710 [A. B.]
| ABSTRACT |
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| Introduction |
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Patients with advanced ovarian cancer usually are treated with surgery followed by chemotherapy. Treatment planning is directed by various prognostic factors, most notably stage and histological grade. Although histological grade and clinical stage are loosely correlated, high-grade malignancies (G3, G4) may be encountered in stage I disease, and low-grade malignancies may be advanced in stage. Outcome often is poor for patients with high-grade (G3, G4) stage IA/B tumors, stage IC tumors, and stage I clear cell tumors and for patients with higher stage disease. However, this stratification scheme is far from perfect because some patients with low-grade and low-stage tumors progress, and 1020% of patients with advanced stage cancers are cured by a combination of surgery and cisplatin-based therapy. We postulate that these differences in outcome have a genetic basis and that comprehensive genomic analyses will reveal characteristics that can be used to predict response to therapy. Genomic aberrations that are associated with adverse outcome then become targets for gene discovery and ultimately targets for therapeutic development.
Specific genetic aberrations already found in ovarian cancers include amplification and/or overexpression of ERBB2 (1) , MYC (2) , PIK3CA (3) , and AKT2 (4) and mutation or down-regulation of TP53 (5 , 6) , K-RAS (7) , LOT1 (8) , DOC2 (9) , NOEY2 (10) , OVCA1 (11) , and SPARC (12) . However, other genes are likely to be involved. Evidence for their existence comes from identification of numerous regions of recurrent abnormality using classical cytogenetics or CGH3 and from analyses of allelic imbalance. The regions of recurrent abnormality identified in these studies are presumed to encode genes that contribute to ovarian cancer genesis or progression.
Some of these aberrations have been associated with clinical end points such as survival duration, grade, and stage in an attempt to elucidate the nature of ovarian cancer progression and to identify markers that more accurately stratify patients according to clinical outcome. Dodson et al. (13) , for example, suggested that LOH at 6p and 17p was an early event and LOH on 13q and 15q was a late events. Rosen et al. (14) presented evidence for significant amplification of FGF3 (INT2) in advanced stage of ovarian cancer, whereas Tavassoli et al. (15) reported LOH on 5q as an early event because of its high incidence in stage I tumors. In addition, our CGH studies (16) of high- and low-grade tumors suggested that copy number increases at 3q26 and 20q13 might be early events. We also reported a significant association between reduced survival duration and total number of abnormalities detected by CGH (16 , 17) and loss of 16q (17) .
In this report, we extend these studies using a CGH-based, genome-wide approach for identification of genome aberrations in ovarian cancer that are associated with clinical end points. Statistical and graphical methods that aid in visualization of these genome-wide comparisons are presented and used to identify associations with survival duration, grade, and stage. Significant associations with survival duration are further assessed in an expanded set of tumors, using quantitative PCR.
| Materials and Methods |
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Analysis of stained CGH preparations was accomplished using QUIPS
Genetics Imaging Software (Vysis, Downers Grove, IL). Three-color DAPI,
FITC, and Texas red images were acquired using a Zeiss Axioplan
microscope equipped with a cooled CCD camera. Six to eight metaphases
were analyzed in each preparation. Chromosomes were identified
according to their DAPI banding pattern, and green-to-red fluorescence
intensity profiles (±1 SD) were calculated for each chromosome type
from measurements of
10 chromosomes.
Significant gains and losses of relative DNA sequence copy number along each of chromosome type were defined as those for which the mean of green-to-red ratio was >1.25 or <0.75 (16) , respectively. The total number of CNAs for each sample was determined by summing the number of contiguous regions of increased/decreased copy number flanked by regions in which the mean green-to-red ratio was 1.0. The gain or loss of both arms of a chromosome was counted as one event.
Quantitative PCR.
Copy number was assessed at the three loci listed in Table 2
, using quantitative PCR analysis as described by Ginzinger et
al.4
because regions containing these loci frequently were found to be
abnormal in copy number in the CGH study and/or associated with reduced
survival duration. Briefly, test and reference loci were PCR-amplified
in the presence of TaqMan probes carrying donor (FAM) and acceptor
(TAMRA) fluorescence molecules. The amount of donor fluorescence in
each reaction liberated by the exonuclease degradation of the TaqMan
probe during PCR amplification was measured as an indication of the
amount of amplified material. Copy numbers at these loci were
determined relative to a pooled reference comprising six microsatellite
loci (D1S2868, D2S385, D4S1605, D5S643, D10S586, and D11S1315) selected
from regions that showed few copy number abnormalities in the CGH
analyses. Primer sequences for these loci were obtained from the
Whitehead Institute Center for Genome
Research.5
The RCN at each test locus was defined as:
![]() |
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Ct (normal) = Ct (test) - Ct (reference) for normal DNA, and
Ct
(tumor) = Ct (test) - Ct (reference) for
tumor DNA.
Ct(normal) was the mean of measurements on 16 unrelated normal DNAs.
Standard deviations of
Ct(normal) were <0.3 for all test loci. The
pooled SD for all loci was used to calculate a 95% tolerance interval
as described.4
Samples were scored as abnormal at
a test locus if the RCN measured at that locus fell outside of the
tolerance interval of 0.731.37. Thus, DNA copy numbers >1.37 were
scored as having significantly increased RCN, and those <0.76 were
scored as having significantly reduced RCN.
Statistical and Graphical Methods.
Statistical and graphical methods were developed to aid in evaluating
the association of CGH with outcome, grade, and stage. For purposes of
statistical analysis, the entire genome was divided into 245 regions of
equal length. Thus, there were 20 regions for chromosome 1 compared
with 4 regions for chromosome 22. For each tumor, a time to recurrence
indicator was defined to be 1 for recurrent tumors and 0 for tumors
that had not recurred during the follow-up time (i.e.,
observation was censored). CGH information also was recorded as an
indicator for each region: -1 for losses; +1 for gains; 0 for neither
gain nor loss.
The relationship between genome copy number changes and grade or stage was assessed using a 2 x 2 contingency table for each of the 245 regions. Specifically, the numbers of tumors with gain or loss were determined for each region, and the results were assembled into a 2 x 2 table as shown below:
A
2 statistic was computed for each
region and for each type of abnormality (i.e., gain or
loss), defined by:
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To aid interpretation,
2 values were
plotted against distance along genome.
A similar method also was applied to survival data. However, survival analyses were accomplished by fitting Cox proportional hazards models to the CGH abnormality indicators in each region. This model was used to test associations between copy number change, as detected by CGH, and survival time. The Cox model does not require that survival follow a parametric form, but assumes that risk of recurrence or death is increased by a constant factor when the factor is present compared with risk when the factor is not present. It also assumes that risk for several factors is equal to the product of the risks for the individual factors. The Cox model was applied to our data using a function written in S-Plus that included the capability to consider other predictive factors, e.g., stage and grade. Thus, the predictive value of a genome aberration could be determined in the presence of other prognostic factors. The function produced a set of p-values corresponding to the statistical significance of gain or loss at each genomic region. These results were then plotted as signed log p-values, where the sign was negative for regions of loss and positive for regions of gain. p-values were plotted only for regions in which >20% of the tumors had genome copy number abnormalities.
Typically, in a large-scale correlative study, there will be several regions with p-values below the p-values = 0.05 level of significance and a few below p-values = 0.01 because of the large number of tests performed. Statisticians call this the "multiple testing problem." To understand the impact of multiple testing in the present study, we performed a series of 100 random permutation tests in which the relationship between the genomic regions and the outcome of interest (e.g., stage, grade, or survival) was destroyed by permuting the outcomes while leaving the genetic information unperturbed. Results from the permutation tests were analyzed to assess the likelihood that the associations observed in this study had true significance. This approach may also be useful in assessing the significance of associations between outcome and gene expression or gene dosage established for a larger number of loci by array analysis technologies.
| Results and Discussion |
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2 value for loss of 4q, suggesting that this
alteration occurs more frequently in high-grade than low-grade tumors.
The
2 statistic for this change (
19) was
much larger than the largest statistic (13)
found during
permutation testing.
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The total number of CNAs was significantly associated with survival
duration as described in earlier studies (16
, 17)
. In the
earlier studies, patients with tumors with <5 CNAs were found to
survive significantly longer than patients with tumors with >10 CNAs.
The present study also shows this difference (p < 0.001). If the number of CNAs is considered as a continuous variable,
the association with reduced survival duration is also significant
(p = 0.02), based on Cox proportional hazards
model with no other factor. If grade is added, then p = 0.057 for CNAs as a continuous variable, and grade is not
significant (p = 0.92). In this analysis, the
single cut-point that minimizes p is number of
CNAs > 7 versus number of CNAs
7, which has a probability p = 0.08, taking into account not having a priori knowledge of
the best cut-point.
We also analyzed associations between survival duration and genome CNAs
for all regions of the genome. Fig. 2
shows the p-values for the associations of genome CNAs with survival
duration plotted as a function of abnormality location along the
genome. p-values associated with increased copy number are plotted as
positive values, and those associated with decreased copy number are
plotted as negative values. Regions of copy number increase associated
with reduced survival duration included 1q, 3q, and 7q. Regions of copy
number decrease associated with reduced survival duration included 4p,
16q, 18q, and both arms of the X chromosome. The strongest association
with reduced survival duration was with loss of 16q. Moreover, this
association held even for late-stage patients stratified according to
16q status. As expected, we did find associations with
p < 0.05 during permutation testing, suggesting
that some of these associations with survival are likely to have
happened by chance. This motivated our efforts to analyze aberrations
using an alternative copy number analysis technology.
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In summary, we have developed a large-scale strategy for association of genotype with clinical behavior and used it to identify several recurrent abnormalities that are associated with tumor grade and clinical outcome. Regions that are frequently abnormal and associated with altered survival duration are strong candidates for higher resolution analysis and gene discovery and may be useful markers for prediction of clinical outcome.
| FOOTNOTES |
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1 This work was supported by NCI Grant CA64602 and
Vysis. ![]()
2 To whom requests for reprints should be
addressed, at UCSF Cancer Center, 2340 Sutter Street, Room N415, San
Francisco, CA 94143-0808. ![]()
3 The abbreviations used are: CGH, comparative
genomic hybridization; LOH, loss of heterozygosity; DAPI,
4,6-diamidino-2-phenylindole; CNA, copy number abnormality; FAM,
6-carboxyfluorescein; TAMRA, 6-carboxytetramethylrhodamine; RCN,
relative DNA copy number. ![]()
4 D. Ginzinger, T. Godfrey, J. Nigro, D. Moore, M.
Pallavicini, and R. Jensen. Measurement of DNA copy number at
microsatellite loci using quantitative real time PCR analysis. Cancer
Res., in press, 2000. ![]()
Received 12/ 9/99. Accepted 8/16/00.
| REFERENCES |
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