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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Clin Cancer Res. Author manuscript; available in PMC 2010 May 15.
Published in final edited form as:
PMCID: PMC2684570
NIHMSID: NIHMS103143

Chromosomal instability and copy number alterations in Barrett's esophagus and esophageal adenocarcinoma

Abstract

Purpose

Chromosomal instability, as assessed by many techniques, including DNA content aneuploidy, LOH, and comparative genomic hybridization, has consistently been reported to be common in cancer and rare in normal tissues. Recently, a panel of chromosome instability biomarkers, including LOH and DNA content, has been reported to identify patients at high and low risk of progression from Barrett's esophagus (BE) to esophageal adenocarcinoma (EA), but required multiple platforms for implementation. Although chromosomal instability involving amplifications and deletions of chromosome regions have been observed in nearly all cancers, copy number alterations (CNAs) in premalignant tissues have not been well characterized or evaluated in cohort studies as biomarkers of cancer risk.

Experimental Design

We examined CNAs in 98 patients having either BE or EA using BAC array CGH to characterize CNAs at different stages of progression ranging from early BE to advanced EA.

Results

CNAs were rare in early stages (<HGD) but were progressively more frequent and larger in later stages (HGD and EA), including high level amplifications. The number of CNAs correlated highly with DNA content aneuploidy. Patients whose biopsies contained CNAs involving more than 70 Mbp were at increased risk of progression to DNA content abnormalities or EA (HR=4.9, 95% CI 1.6-14.8, p=0.0047), and the risk increased as more of the genome was affected.

Conclusions

Genome wide analysis of CNAs provides a common platform for evaluation of chromosome instability for cancer risk assessment as well as identification of common regions of alteration that can be further studied for biomarker discovery.

Keywords: copy number alteration, Barrett's esophagus, esophageal adenocarcinoma, array CGH, premalignant, aneuploidy, chromosomal instability

Introduction

Barrett's esophagus (BE) is a premalignant condition in which the squamous epithelium that normally lines the esophagus is replaced with an intestinal metaplasia as a result of chronic gastroesophageal reflux disease (GERD). Patients with BE have at least a 15-fold increased risk for development of esophageal adenocarcinoma (EA)1, a cancer that has increased in incidence by more than 600% over the past 30 years2. Treatment options for EA are limited, and the majority of patients who develop EA present initially with advanced disease, with 5 year survival rates of 13.7%3. Patients with BE are typically placed in surveillance programs for the early detection of cancer, but the rate of progression from BE to EA is estimated to be only 0.7% per year4, and the vast majority of BE patients will neither develop nor die from EA5. Thus, there is a strong clinical need for biomarkers that can discriminate between those who are unlikely to progress to cancer, who should be reassured and removed from frequent surveillance because of their low risk, and those at higher risk, who need frequent surveillance or intervention to prevent cancer.

Chromosomal instability involving DNA copy number alterations (CNAs) are frequently observed in many types of cancer, including those of the pancreas, lung, colon, breast and prostate, among others6. CNAs have been used as biomarkers for cancer prognosis in multiple studies7, 8, but there are few longitudinal studies of CNAs as predictors of progression to cancer. Most studies analyzing CNAs that occur during neoplastic progression in vivo examine primarily cancer samples. CNAs in patients with EA have been examined primarily by traditional comparative genomic hybridization (CGH)9-20. Traditional CGH studies of EA have typically reported widespread alterations throughout the genome, but with low resolution with respect to specific chromosomal regions being affected. Recently, Nancarrow et al reported a study of EA using SNP arrays, confirming widespread and extensive chromosomal alterations in advanced EAs21.

The utility of CNAs as biomarkers of risk assessment for progression to EA at earlier stages of neoplastic progression in BE, however, has not been well studied. Two groups have examined a small number of premalignant BE samples using traditional CGH. Croft et al, found copy number gains on multiple chromosomes in at least 40% of 15 high-grade dysplasias (HGD)22, while Riegman et al, found frequent gains and losses in ten HGD and nine low-grade dysplasia (LGD) samples, with no alterations observed in ten metaplasias23. These studies were limited by the lack of resolution of traditional CGH and the fact that the Riegman study only examined premalignant BE in specimens in which cancer had already arisen. In a more recent small study of six selected patients whose CDKN2A and TP53 status was known, it was demonstrated that changes in chromosomal instability (LOH and CNAs) could be detected over time, but, like the other studies, these patients and samples were highly selected and were not representative of the spectrum of BE in patients in general24. While these studies focused upon discovery of specific chromosomal alterations, well designed biomarker validations studies will be required to bring chromosome instability biomarkers to the clinic25 A recent study evaluated a panel of tumor suppressor genes and DNA content biomarkers, including CDKN2A (LOH, methylation, mutation), TP53 (LOH, mutation), tetraploidy and aneuploidy26. Only the chromosome instability biomarkers, 9p LOH, 17p LOH, tetraploidy and aneuploidy, provided independent cancer risk assessment in multivariate analysis. However, this panel required a combination of platforms, including short tandem repeat polymorphisms for LOH and DNA content flow cytometry, which would be difficult to implement clinically.

Here we report for the first time evaluation of genome–wide chromosome instability analysis of copy number alterations using BAC array CGH in 174 samples from a cohort of 98 patients with diagnoses ranging from BE negative for dysplasia to advanced EA, a population representative of the range of BE stages of neoplastic progression and a sample size that provides statistical power to quantify early and relatively rare CNA events. BAC array CGH allows genome wide analysis of copy number alterations and much more precise location of gains and deletions than traditional CGH27. DNA content flow cytometric data and patient characteristics were also available for each of the samples allowing us to validate array CGH as a measure of aneuploidy, a previously validated biomarker of progression from BE to EA28. We further investigated array CGH as a common platform to assess chromosomal instability in a prospective biomarker validation study. This study extends previous discovery research from many sources into a translational research cohort study25 demonstrating that genome wide assessment of copy number identifies BE patients with an increased risk for progression.

Methods

Study Subjects and Tissue Acquisition

The Seattle Barrett's Esophagus Study was approved by the Human Subjects Division of the University of Washington in 1983 and renewed annually thereafter with reciprocity from the Fred Hutchinson Cancer Research Center (FHCRC) Institutional Review Board from 1993 to 2001. Since 2001, the study has been approved by the FHCRC IRB with reciprocity from the University of Washington Human Subjects Division. The 72 non-cancer participants in this study (Table 1) had their baseline endoscopy performed between 1995 and 1999 and were followed for a period of six to 140 months. Patients were categorized on the basis of maximal histology at baseline and were grouped into three categories: less than high grade dysplasia (<HGD), which includes diagnoses of metaplasia without dysplasia, indefinite for dysplasia and low grade dysplasia; high grade dysplasia (HGD) and esophageal adenocarcinoma (EA). These categories were chosen based upon observer variation studies, which show best reproducibility when diagnoses were divided between HGD/EA and low-grade/indefinite/metaplasia29, 30, and upon prospective studies that show risk of progression to EA is markedly greater for HGD than for lower grades31, 32. EA samples came from esophagectomy specimens. The distribution of patients in this study by gender, age, BE segment length, percentage of patients progressing to EA during follow-up and histologic diagnosis is similar to that of the overall Seattle Barrett's Esophagus Cohort, with the exception of a lower percentage of patients with 17p LOH. This lower representation is due to the amount of DNA required for analysis by BAC array, which precluded the use of some samples. Forty-two of the 98 patients (43%) and 40 of the 83 (48%) non-EA patients in this study had more than one sample available for analysis (23 patients had two samples, nine had three, and five patients each had four and five samples). Different biopsies from six of the patients with EA, and different biopsies from separate endoscopies from two patients with HGD and eight of the <HGD patients were examined for genetic alterations using SNP arrays in a study published previously33; however, the current study was designed independently.

Table 1
Cohort characteristics

Endoscopic biopsy protocols used in the Seattle Barrett's Esophagus Study have been published previously26. Briefly, four quadrant biopsies for histology were taken every 1 cm (for patients with high-grade dysplasia and DNA content tetraploidy or aneuploidy) or every 2 cm (for patients without high-grade dysplasia or DNA content tetraploidy or aneuploidy) at intervals ranging from every 6 months to 3 years, as described previously. Additional biopsies at levels adjacent to those used for histologic evaluation were taken every 2 cm for molecular analyses; a subset of these was used in this study. Although the biopsies used for CGH were not evaluated for histology, they came from within a region of the columnar-lined esophagus identified by an expert Barrett's endoscopist (PLB) that was histologically verified as Barrett's esophagus by an expert GI pathologist (RDO)34. All biopsies examined in this study were taken from either the baseline endoscopy or from a surgical resection. Endoscopic biopsies were placed into cryovials with media with 10% DMSO (dimethyl sulfoxide) held on wet ice until frozen and stored at -70°C.

Ki67/DNA Content Multiparameter Flow Cytometry and Sorting

Frozen endoscopic biopsies were prepared for flow cytometry as described previously26. The suspension of unfixed nuclei from each biopsy was distributed into separate tubes with approximately 10% for DNA content flow cytometric analysis and 90% for multiparameter Ki67/DNA content cell sorting. The DAPI (10 μg/ml, Accurate Chemical, Westbury, NY) saturated nuclei for single parameter DNA content flow cytometry were never centrifuged and were syringed using a 25 gauge needle immediately before acquisition on the flow cytometer. DNA content analysis was performed using MultiCycle software (Phoenix Flow Systems, San Diego, CA) with a peak vs. area gate to exclude doublets and with “sliced nucleus” background correction. The remaining nuclei were incubated with DAPI and either directly conjugated Ki67–RPE (phycoerythrin) or isotype control–RPE (DAKO R0840, Carpinteria, CA) and cell sorted to purify the proliferating BE epithelial cells from non-proliferating G0 cells into cell cycle fractions including G1, 4N (G2/tetraploid), or aneuploid populations as previously described26.

Array characteristics

Characteristics and construction details of the BAC arrays used in this study have been described previously35. The BAC arrays consist of 4342 BAC clones with median spacing 402 kb spotted in duplicate, with 99% of map locations verified by FISH. The identity and locations of individual BACs in the array can be found at the CHORI BAC/PAC resources website (FISH Mapped Clones V1.3 Download).

BAC array preparation

Probe labeling and hybridization conditions have been described previously35. Ten nanograms of digested genomic DNA were used as input into labeling reactions for each biopsy sample and labeled with Cy5. A single male reference DNA (Promega, Madison, WI) was used as a normal control for all samples and labeled with Cy3. The use of a single normal control raises the possibility that constitutive copy number variations may be misinterpreted as somatic genetic events36. We have examined the most frequent alterations described in Table 4a and have noted those that overlap with regions found to have CNV in at least one analyzed population at a frequency greater than 10% (Database of Genomic Variants37).

Table 4
Chromosome regions with CNAs associated with future development of EA or DNA content abnormalities

Preliminary BAC array data processing

Arrays were scanned with a GenePix 4000A scanner (Axon Instruments, Union City, CA) and data were processed using GenePix 3.0 image analysis software. Log2 ratio of sample fluorescence to control (Cy5/Cy3) for each spot on the array was determined and all ratios were normalized and corrected for intensity-based location adjustment using a block-level loess algorithm38. The average log2 ratio for the duplicate spots was determined for each BAC on the array: in cases where one of the duplicates failed, the log2 ratio was calculated from the remaining spot. Any BACs for which the duplicates differed by more than 20% were classified as no data. Any arrays having more than 20% bad spots were not included in the analysis.

BAC array data analysis

Statistical methods were applied to identify CNAs in the background of potentially noisy log2 ratios generated in the array CGH experiments. The wavelet method described by Hsu, et al39, was used to denoise the BAC array data, help identify BACs with CNAs and the breakpoints of each CNA event. The wavelets method is a spatially adaptive nonparametric method that can accommodate the abrupt changes in copy numbers and different sizes of aberrations. It has been demonstrated that the wavelets-based data denoising yields greater power in the downstream statistical analyses and generates more comparable log2 ratios across samples than raw data. The predicted log2 ratios after wavelets denoising were then used to determine the calls for each BAC as a) copy number loss, b) copy number gain, c) no change or d) no data. The log2 ratio for each BAC in a sample was plotted along its position on each chromosome and the regions that were called gain and loss identified. Contiguous regions of loss, defined as a continuous region of BACs all having the same call of copy number gain or loss, were called gain or loss events, respectively, and used in the by-event analyses. Since there was more than 1 sample available for 43% of the patients studied, we established a by-patient call for each BAC for that patient as follows: a) if all the samples with data for the BAC had the same call, that consensus call was used, b) if any sample had a combination of copy number gain or loss and no change, the call was gain or loss, respectively, c) in the rare (<0.01% of the BACs examined) cases where one sample had a gain and another had a loss, the majority call was used (e.g., 2 samples with loss and one with gain would be called a loss at that BAC), and d) if all samples from a patient were no data, the BAC was classified as no data.

Data from individual BACs were not used in further analyses if >40% of the BACs in a group of patients (e.g., <HGD) had a call of no data, suggesting poor hybridization for that particular BAC on the array. Data from chromosomes X and Y were not included in further analyses since a common male DNA was used as a normal control, making gains and losses on these chromosome difficult to quantify for all samples. Any BACs that showed a pattern of alterations that correlated significantly with a particular manufacturing batch (t-test with p<0.05 between different manufacturing batches) were considered artifacts and were not included in the analyses (29 total).

Identification of significant copy loss and gains and comparison among different progression stages

For the largest sub-group of patients in this study (72 <HGD patients) to have 99% confidence that loss at a given BAC is significantly different than no loss (null hypothesis), the cutoff is 7 patients, which corresponds roughly to 10% of the patients examined (Fisher's exact test). Therefore, cutoffs on the figures and in our analysis were set at 10%. Due to the higher frequency of alterations in the EA samples, an arbitrary cutoff of 40% was used to identify those alterations that were most frequent in the EA samples. Tukey's test was used to evaluate associations between the mean numbers of alterations present at different stages of progression. The amount of the genome affected by CNAs was calculated by summing the size of regions affected by gains and losses for each non-EA patient; if a patient had more than one sample, the sample with the greatest amount of the genome affected was used for subsequent analyses. Cox regression model was used to determine if there was a significant relationship between total CNA size and the development of either a DNA content abnormality or EA at a later time point during patient follow-up. As well, Cox regression analysis was used to identify BACs with CNAs associated with development of DNA content abnormalities or EA during follow-up.

Results

Characteristics of the cohort are shown in Table 1. We first examined the frequency of copy number alterations in patients without HGD, in those with HGD, and in those with EA. Examples of representative CNAs are shown in Supplemental Figure 1. Evidence of chromosomal instability, as assessed by the percent of BACs with a copy number alteration, increased significantly in samples from patients without HGD (1.3%), to those with HGD (4.7%), to EA (30.4%) (Supplemental Table 1) (p<0.0001, Tukey's test).

We observed different chromosome instability patterns in the frequency and size of CNAs across the spectrum of progression in BE. Throughout the genome, patients with more advanced histology (HGD, EA) had a greater number of copy number change events (any contiguous region of the genome having the same copy number change) and the events were larger than in <HGD. There was a significant increase in number of CNA loss events as well as increased size of those events when comparing patients with <HGD, HGD and EA (Table 2a) (p<0.0001 for all comparisons). We found similar results when we examined loss events at a specific locus, p16/CDKN2a/ARF on chromosome 9p (Table 2b and Supplemental Figure 2). The same CNAs were observed in multiple samples from the same patient across as much as 8cm of the BE segment in the esophagus (data not shown), indicating clones with CNAs undergo clonal expansion similar to other types of alterations40.

Table 2
Average size of loss and gain events

DNA content flow cytometric abnormalities are manifestations of chromosomal instability in many types of cancer and they have been reported to carry an increased risk for progression from BE to EA26, 41, 42. We examined the relationship between the number of BAC alterations and DNA content ploidy for each of the 98 patients in this study (Figure 2). The median number of BAC alterations in patients with a DNA content aneuploid population was significantly higher than those with only diploid cell populations (1275 vs 24.5, p<0.0001). The vast majority of the diploid samples (141/155; 91%) had less than 180 BAC alterations, compared to 0/19 aneuploid samples. Using an empirical thresholding method, we determined a threshold of 760 BACs with CNAs would allow identification of aneuploid samples with a sensitivity and specificity of 93% and 98%, respectively. Results from bootstrap analysis showed a robust threshold range, with thresholds from 200 to 800 BAC alterations for the identification of aneuploid samples leading to mean sensitivities of 84.0% to 94.8% and specificities of 92.2% to 99.4%, respectively. We quantified the relationship between total number of BAC alterations and probability of being aneuploid (p) with logistic regression equation M1, where N is total number of BAC alterations per sample (95% CI for the two parameters, -18.6 to -20.1 and 2.0 to 2.2, respectively). This model predicts aneuploidy accurately using the overall number of BACs displaying CNAs.

Figure 2
Overall number of copy number alterations in diploid and aneuploid samples associate with aneuploidy as measured by flow cytometry

We then examined genome-wide assessment of copy number abnormalities as a measure of chromosome instability for patient risk assessment for progression to EA or validated intermediate endpoints. Patients whose biopsies contained copy number alterations involving more than 70 Mbp of the genome had a significantly increased risk of progressing to DNA content abnormalities or EA during follow-up (HR=4.9, 95% CI 1.6-14.8, p=0.0047), and the risk increased as more of the genome was affected.

The most common region of copy number alteration in patients without HGD or EA was loss in and around the p16 locus on chromosome 9p (42.9%), along with two other areas distinct from p16 on chromosome 9p: from 10.4 Mb to 11.8 Mb (18.3%) and from 25.5 Mb to 27.5 Mb (19.4%) (Figure 1a and Table 3a). Losses were also observed around 185Mb on chromosome 1q (37.5% of patients), and at 101 Mb on chromosome 8 (41.2%). Other losses at single BACs at frequencies of 10% or more in <HGD patients are listed in Table 3a. The most frequent gains in the <HGD patients involved the very ends of the p arms of chromosomes 17 and 18 (29.2% of patients for each), and gains involving predominantly whole chromosomes were observed on chromosomes 8 (in four patients) and 18 (six patients).

Figure 1a- c
Frequency plots of gains and losses throughout the genome in patients with <HGD (a), HGD (b), and EA (c)
Table 3
List of most frequent chromosomal regions of gain or loss in patients with BE or EA

Copy number alterations were more common in patients with HGD and involved larger regions of the genome (Figure 1b and Table 3a). The region in and around the p16 locus was again lost in a large fraction of the patients (45.5%), but losses were observed in more than 10% of patients involving large regions of chromosomes 1, 2, 5, 6, 7, 8, 9, 10, 11, 13, 14, 16, 17, 18, and 22. Gains were seen on chromosomes 3, 5, 8, 14, 16, 17, 18, and 19. Some regions, such as chromosome 5p, 8q, 14q, and 17p showed amplification in one subset of patients and deletion in another (Table 3a). We used Cox regression analysis to identify regions of the genome significantly associated with future development of DNA content abnormalities or EA (Table 4). While the number of EA and DNA content abnormality events in this cohort were small (8 EA and 16 DNA content events out of 71 patients with follow-up data), these data indicate genomic regions that may be of interest in future biomarker studies.

The copy number alterations observed in EA patients indicate accumulation of complex, multiple amplification and deletion events (Figure 1c and Table 3a). All samples from these patients were aneuploid by flow cytometry. The high frequency and large average size of alterations in the EA samples makes it difficult to identify individual gene alterations that may be required for progression to cancer; however, we have listed the regions with most frequent copy number alterations (occurring in at least 40% of the patients) along with potential genes of interest in those regions in the EA patients in Table 3a. High-level amplification events were observed only in EA patients and in a single HGD patient who subsequently progressed to EA (Table 3b).

Discussion

Our study advances validation of chromosome instability as a biomarker for risk assessment in BE by demonstrating for the first time that array CGH can be used as a common platform to assess chromosomal instability as a predictor of progression in BE. The current standard for risk stratification for patients with BE, dysplasia classification, has several limitations, including observer variation in diagnosis and requirements for large numbers of biopsies29, 30, 34. In fact, even what constitutes the histologic definition of Barrett's esophagus is a matter of ongoing debate43, 44. In this prospective study, we have examined samples from a cohort of patients representing the spectrum of BE, including both high-risk patients that progressed to EA at a later time point and low-risk patients who did not develop EA, in some cases for almost 12 years of follow up. We have shown that array CGH provides a common platform for assessing genome-wide and locus specific chromosomal instability compared to previous platforms that required combined STR analysis of LOH and DNA content by flow cytometry26. We have demonstrated in this cohort study that array CGH can assess genome-wide chromosome instability, like the previously validated biomarker DNA content flow cytometry, and that array CGH can be used to detect patients at increased risk for progression to validated intermediate endpoints such as DNA content abnormalities and EA.

Somatic CNAs are thought to occur rarely in non-neoplastic tissues, and the high frequency of their occurrence across the spectrum of cancer types indicates that loss of genome integrity plays an important role in neoplastic progression. The use of a genome wide measure of genetic instability (CNAs in this study) is appealing since all cancers progress through some type of genetic instability (reviewed recently in45, 46). While some cancers may display little overall copy number instability, e.g., MIN cancers, these generally represent a minority of solid tumors, and certainly a minority of EAs47. Flow cytometric analysis of ploidy has been a validated standard for determining gross chromosomal instability, and aneuploid or tetraploid populations are associated with increased risk of EA in patients with BE26, 28, 42, yet differences in DNA content greater than 10% compared to normal cells (equivalent to ~300Mbp) are required before a flow cytometric determination of aneuploidy can be made confidently. Our results indicate that array CGH is able to identify patients with a significantly increased risk of progression when only 70Mbp of the genome was involved in CNAs, which is less than one-quarter of the changes required by flow cytometry. These results were obtained using only a few samples from each patient - in some cases only a single biopsy from an 11-cm Barrett's segment. Since we know multiple clones can exist in a BE segment, one biopsy every two cm sampling of the segment as reported by Galipeau et al26 is likely to improve the determination of patient risk. As well, the use of SNP arrays that can measure both LOH and CNAs at a much higher density than BAC arrays would be the most direct means of extending this study to a larger number of patients and testing its utility in the clinic.

The data obtained from this cohort study allow us to identify and examine potentially interesting regions of the genome undergoing CNAs in patients at different stages of progression, extending the findings from earlier pilot studies that examined patients with primarily advanced disease, and did not evaluate the utility of a measure of chromosomal instability as an indicator of progression risk24, 33. We found 9p loss encompassing p16 throughout progression, losses on chromosome 5q, 13q and 18q in HGD and EA and high level amplification at ErbB2 on chromosome 17q in EA patients, all of which have been previously identified using different approaches by multiple investigators21, 48. While localized loss of p16 may be too frequent in early BE to be a discriminator of progression risk, these other alterations, as well as expansion of 9p losses to regions beyond the p16 locus, may be robust components of a chromosome instability array platform for further validation in future biomarker validation studies (see also Table 4). Two regions of the genome that have been frequently reported as altered in BE are the FHIT locus on chromosome 3p and the TP53 locus on chromosome 17p24, 33. We did not detect FHIT alterations since there was no BAC spanning the locus on our arrays, and the frequency of loss events at TP53 was just below the threshold for reporting (10% of HGD, 33% of EA patients). However, loss of heterozygosity of TP53 can involve copy neutral mechanisms and/or copy gain in nearly 70% of cases49, so simple copy loss assessment likely under represents the frequency of chromosome instability at this locus.

We also detected examples of clones with mutually exclusive CNA events (i.e., amplification in one patient, loss in another) that can be selected at different points during progression. One example is the prostaglandin-endoperoxide synthase 2 (PTGS2 or COX2) gene, which is overexpressed in a wide variety of cancers50-52. We found amplification of COX2 in 27% of the EA cases, but also observed copy loss of COX2 in 37% of <HGD. It is possible that the environment of the reflux exposed esophagus, with its associated chronic inflammation, selects for loss of the COX2 gene. There was a trend for fewer patients with deletion in the region of COX2 to develop DNA content flow cytometric abnormalities during follow-up (4/29, 14%) compared to those lacking the deletion (12/43, 28%), although the difference in this study was not significant. A recent meta-analysis of COX2 expression in BE and EA53 concluded that there was conflicting evidence over the role of COX2 in neoplastic progression in BE; our finding of a subset of patients having a deletion in the COX2 locus may explain this heterogeneity in previous studies.

Previous studies that examined primarily EA samples9-21 reported widespread CNAs throughout the genome, and those that examined a small number of BE samples22, 23 found far fewer alterations at earlier stages. The previous study by Lai et al24, using high density Affymetrix arrays, demonstrated alterations within a patient can become more frequent and larger during disease progression, but only examined six highly selected patients that had developed specific genetic alterations. The most recent study by Li, et al, a pilot discovery study using a 33K SNP array to investigate LOH and CNAs in 34 primarily high-risk patients with BE and 8 patients with EA, also found increased CNAs in later stages of progression and an association between number of alterations and aneuploidy33. The study presented here extends these earlier observations by demonstrating that a genome wide measure of CNAs can be used as a measure of risk of progression to DNA content abnormalities or EA in a prospective cohort study. Genome-wide arrays have potential for providing accurate cancer risk assessment using a single platform in patients with BE and represents an advanced stage of validation for chromosome instability as a biomarker of cancer risk ready for further validation in larger patient cohorts with prolonged follow-up25.

The translation of biomarkers identified in discovery studies to a clinical setting requires demonstrating the utility of a biomarker for assessing risk of progression in prospective cohort studies and adapting the biomarkers to platforms that can be standardized for clinical use. The biomarker panel of 9p LOH, 17p LOH and DNA content that was validated in a 10 year prospective study is able to identify patients at both high and low risk for developing EA, but requires short tandem repeat polymorphisms for assessing LOH and DNA content flow cytometry to detect ploidy alterations, both of which were state of the art when the study was designed in the mid 1990s26. As we report here, advancing array technology now can provide a common platform for detecting chromosome instability that is able to detect aneuploid populations, identify patients at risk for future development of ploidy alterations or EA, and identify specific chromosomal regions that undergo frequent CNAs as candidates for additional evaluation.

Supplementary Material

Suppl Fig 1

Suppl Fig 2

Suppl Table 1

Acknowledgments

We would like to thank Gao Zhang for creating data sets for wavelets analysis, Dave Cowan for database management, Valerie Cerera, Christine Karlsen, and Kamran Ayub for sample procurement and processing, Patricia Galipeau for manuscript review, the FHCRC Array facility for assistance with BAC array processing, and the participants in the Seattle Barrett's esophagus cohort whose participation makes this study possible.

Supported by NIH K07CA089147, PO1CA91955 and the Ryan Hill Foundation (TGP).

Footnotes

Statement of Clinical Relevance Barrett's esophagus (BE) is the only known precursor to esophageal adenocarcinoma (EA), but the vast majority of patients with BE will die of unrelated causes. Identification of biomarkers that discriminate between patients at low vs. high risk of progressing to cancer is necessary to improve patient outcomes. Here, we report an array comparative genomic hybridization (CGH) analysis of copy number alterations in a cohort of 98 patients with either premalignant BE or EA. In addition to determining the frequency and locations of deletions and amplifications occurring before the development of cancer, genome wide analysis of copy number alterations can identify DNA content aneuploid populations, as well as patients at risk for progression to DNA content abnormalities or EA. Array CGH provides a single platform for validation of chromosomal instability as a biomarker for cancer risk assessment that can be further evaluated in larger studies.

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