
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Imaging, Diagnosis, Prognosis |
Authors' Affiliations: Departments of 1 Ophthalmology and Visual Sciences and 2 Pathology and Immunology, Washington University, St. Louis, Missouri and 3 Tumori Foundation, San Francisco, California
Requests for reprints: J. William Harbour, Department of Ophthalmology and Visual Sciences, Washington University, 660 South Euclid Avenue, Box 8096, St. Louis, MO 63110. Phone: 314-362-3315; Fax: 314-747-5073; E-mail: harbour{at}wustl.edu.
| Abstract |
|---|
|
|
|---|
Experimental Design: Gene expression profiling, fluorescence in situ hybridization (FISH), and array comparative genomic hybridization (aCGH) were done on 67 primary uveal melanomas. Clinical and pathologic prognostic factors were also assessed. Variables were analyzed by Cox proportional hazards, Kaplan-Meier analysis, sensitivity, specificity, positive and negative predictive value, and positive and negative likelihood ratios.
Results: The gene expressionbased molecular classifier assigned 27 tumors to class 1 (low risk) and 25 tumors to class 2 (high risk). By Cox univariate proportional hazards, class 2 signature (P = 0.0001), advanced patient age (P = 0.01), and scleral invasion (P = 0.007) were the only variables significantly associated with metastasis. Only the class 2 signature was needed to optimize predictive accuracy in a Cox multivariate model. A less significant association with metastasis was observed for monosomy 3 detected by aCGH (P = 0.076) and FISH (P = 0.127). The sensitivity and specificity for the molecular classifier (84.6% and 92.9%, respectively) were superior to monosomy 3 detected by aCGH (58.3% and 85.7%, respectively) and FISH (50.0% and 72.7%, respectively). Positive and negative predictive values (91.7% and 86.7%, respectively) and positive and negative likelihood ratios (11.9 and 0.2, respectively) for the molecular classifier were also superior to those for monosomy 3.
Conclusions: Molecular classification based on gene expression profiling of the primary tumor was superior to monosomy 3 and clinicopathologic prognostic factors for predicting metastasis in uveal melanoma.
Consequently, detection of monosomy 3 has now been adopted by most centers around the world as the gold standard for metastatic prediction in uveal melanoma (1114). Indeed, prospective clinical trials are in the planning stages around the world that intend to use monosomy 3 as an entry criterion for preemptive antimetastatic interventions in high-risk uveal melanoma patients. However, the sensitivity and specificity of monosomy 3, essential indicators of its utility as a clinical marker of metastatic risk, have not been reported, and it is possible that other available molecular classifiers may be superior to monosomy 3 for individualized patient management.
We and others recently reported a molecular classification of uveal melanomas based on gene expression profile that strongly predicts metastasis (15, 16). Tumors with the class 1 gene expression signature have a low risk of metastasis, and those with the class 2 signature have a high risk of metastasis (15). Our initial study was done on tumor tissue obtained after eye removal, but we have also shown that gene expression profiling can be done accurately on fine-needle biopsy specimens obtained before radiotherapy in uveal melanoma patients who do not require eye removal (17). Although these initial studies showed a strong association between the class 2 signature and monosomy 3, the former seemed to be superior in prognostic accuracy (15).
In this study of 67 uveal melanoma patients, the largest outcome study of its kind to date in uveal melanoma, we compare the prognostic accuracy of the gene expressionbased classifier versus monosomy 3 detected by FISH and CGH.
| Materials and Methods |
|---|
|
|
|---|
Microarray expression profiling. Microarray gene expression values were obtained on Affymetrix U133A, U133Av2, and Illumina Ref8 chips. Analysis of Affymetrix data was described previously (15, 17, 18). Illumina data were normalized by the rank invariant method using BeadStation software,4 log2 transformed, and analyzed by principal component analysis using Spotfire software.5 Assignment of tumors to class 1 and class 2 was done by a weighted voting algorithm using GeneCluster2 software6 as described previously (15, 17).
Fluorescence in situ hybridization. Dual-color FISH was done as described previously (19). Briefly, paraffin-embedded tissue sections were deparaffinized with Citrisolv (Fisher Scientific, Pittsburgh, PA), dehydrated in 100% ethanol, subjected to target retrieval by steam heating in citrate buffer (pH 6.0) for 20 min, digested in pepsin solution (4 mg/mL in 0.9% NaCl) for 20 min at 37°C, rinsed in 2x SSC (300 mmol/L sodium chloride and 30 mmol/L sodium citrate) at room temperature for 5 min, and air dried. A Spectrum Greenlabeled chromosome 7 centromeric DNA probe, CEP7(D7Z1) (Vysis, Inc., Downers Grove, IL), was paired with a Spectrum Orangelabeled chromosome 3 centromeric probe, CEP3(D3Z1) (Vysis). Probes were diluted 1:50 in t-DenHyb buffer (Insitus Laboratories, Albuquerque, NM). Hybridization mix was applied to sections followed by denaturation in a 90°C slide moat (Boekel Scientific, Feasterville, PA) for 13 min. Hybridization was done overnight at 37°C in a humidified chamber. Slides were then washed in 50% formamide/1x SSC for 5 min and then twice in 2x SSC for 10 min each at room temperature. Slides were allowed to air dry, and then, nuclei were counterstained with 4',6-diamidino-2-phenylindole (Insitus Laboratories). Sections were visualized on an Olympus BX60 fluorescent microscope (Olympus, Melville, NY). At least 100 nuclei were analyzed for each tumor. A threshold of 30% nuclei with one chromosome 3 signal and two chromosome 7 signals was established for making the call of monosomy 3.
Array CGH. Array CGH (aCGH) was done using human bacterial artificial chromosome arrays. Previously published samples were analyzed by the Microarray Shared Resource at the Comprehensive Cancer Center, University of California (San Francisco, CA) using a microarray-based platform containing a genome-wide collection of genomic contigs as described previously (15, 20). Newer, previously unpublished samples were analyzed by the Microarray and Genomics Facility of the Roswell Park Cancer Institute (Buffalo, NY) using an array platform containing
6,000 bacterial artificial chromosome clones.7 One microgram of reference and test sample genomic DNA were individually fluorescently labeled using the BioArray CGH Labeling System (Enzo Life Sciences, Farmingdale, NY). DNA was hybridized to the arrays for 16 h at 55°C using a GeneTAC hybridization station (Genomic Solutions, Inc., Ann Arbor, MI). The hybridized aCGH slides were then scanned using a GenePix 4200A Scanner (Molecular Devices, Sunnyvale, CA) to generate high-resolution (5 µm) images for both Cy3 (test) and Cy5 (control) channels. Image analysis was done using the ImaGene (version 6.0.1) software from BioDiscovery, Inc. (El Segundo, CA). A loess-corrected log2 ratio of the background-subtracted test/control was calculated for each clone to compensate for nonlinear raw aCGH profiles in each sample. A log2 average raw ratio of >0.5 was used as the threshold for significant DNA copy number deviations.
Statistical analysis. Fisher's exact test was used to assess the significance of association between two categorical variables. Cox univariate proportional hazards was used to assess time-dependent association with metastasis for categorical and continuous variables. Kaplan-Meier analysis was used to assess time-dependent association with metastasis for categorical variables. Continuous variables were dichotomously categorized by the value that maximized sensitivity and specificity by receiver operating characteristics analysis. Variables that exhibited a significant association with metastasis were further analyzed by Cox multivariate proportional hazards modeling to assess their relative contribution to metastasis. Sensitivity, specificity, likelihood ratios, and predictive values were assessed for all clinical, pathologic, and molecular factors. In analysis A, metastasis was used as the end point. In analysis B, class 2 gene expression profile was used as a surrogate end point in metastasis-free patients. All statistical analyses were done using MedCalc software version 9.0.0.1.
| Results |
|---|
|
|
|---|
|
|
|
|
|
| Discussion |
|---|
|
|
|---|
10% of cases that require enucleation but also for the vast majority that are treated with radiotherapy and other globe-sparing methods. There are several potential explanations for the superiority of gene expression profiling over monosomy 3. From a technical standpoint, FISH is more challenging in uveal melanoma than in some other cancers due to its dense cellularity and elongated nuclei that weave in and out of the plane of section. The former makes it difficult to establish which signals belong to which cells, whereas the latter increases the likelihood of underestimating signal counts (false negatives). To complicate this problem, monosomy 3 is usually heterogeneous within a given tumor (Fig. 2B). Consequently, the percentage of nuclei with one chromosome 3 that is set as a threshold for calling the tumor monosomy 3 is somewhat arbitrary and may lead to false negatives or false positives. This heterogeneity for monosomy 3 can also lead to sampling error. In contrast, we have not found heterogeneity in the gene expression profile when multiple areas of the same tumor are sampled (data not shown). Although these pitfalls are partially overcome by using fresh cytologic preparations rather than paraffin-embedded tissue (data not shown), there are still artifacts that hinder interpretation. Most notable is the tendency for signal splitting (appearance of two closely positioned signals at the site of a single centromere), which is common with the chromosome 3 probe. For reasons that are unclear, this phenomenon is variable and is more prominent in some specimens than others, leading to potential overestimation of centromere numbers. In addition to these problems, some tumors sustain interstitial deletions on chromosome 3 rather than loss of the whole chromosome (22), which likely would be undetected by FISH, leading to false-negative calls.
Because of these shortcomings of FISH, we also assessed chromosome 3 status by aCGH, which is a quantitative technique that overcomes many of the technical obstacles of FISH. Nevertheless, the performance of aCGH was still inferior to gene expression profiling. This may be due, at least in part, to the inability of aCGH to detect isodisomy 3, which occurs in some uveal melanomas when there is loss of one chromosome 3 and duplication of the remaining, presumably abnormal chromosome 3 (23). In addition, it seems likely that gene expression profiling represents a "snapshot" that captures more of the functional complexity of the tumor vis-à-vis metastatic potential than does a simple chromosomal marker, such as monosomy 3. Consistent with this idea, we recently showed that the gene expression pattern exhibited by the class 2 tumors was consistent with a primordial, epithelial-like phenotype, which may indicate that class 2 tumors contain more stem-like cancer cells with increased metastatic capacity (18).
Based on these results, plans are under way to optimize and validate the molecular classifier on a larger patient population. Ultimately, this classifier could be used to individualize the intensity and frequency of metastatic surveillance and to guide entry of high-risk patients into clinical trials of preemptive antimetastatic therapies, such as vaccines and targeted molecular agents.
| Footnotes |
|---|
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.
Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/).
Presented in part at the 2006 AACR International Conference on Molecular Diagnostics in Cancer Therapeutic Development, September 12-15, 2006, Chicago, Illinois.
6 http://www.broad.mit.edu/cancer/software ![]()
7 http://microarrays.roswellpark.org ![]()
Received 9/29/06; accepted 12/12/06.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
W. van Gils, E. M. Lodder, H. W. Mensink, E. Kilic, N. C. Naus, H. T. Bruggenwirth, W. van IJcken, D. Paridaens, G. P. Luyten, and A. de Klein Gene Expression Profiling in Uveal Melanoma: Two Regions on 3p Related to Prognosis Invest. Ophthalmol. Vis. Sci., October 1, 2008; 49(10): 4254 - 4262. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Ulmer, J. Beutel, D. Susskind, R.-D. Hilgers, F. Ziemssen, M. Luke, M. Rocken, M. Rohrbach, G. Fierlbeck, K.-U. Bartz-Schmidt, et al. Visualization of Circulating Melanoma Cells in Peripheral Blood of Patients with Primary Uveal Melanoma Clin. Cancer Res., July 15, 2008; 14(14): 4469 - 4474. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. D. Onken, L. A. Worley, and J. W. Harbour A Metastasis Modifier Locus on Human Chromosome 8p in Uveal Melanoma Identified by Integrative Genomic Analysis Clin. Cancer Res., June 15, 2008; 14(12): 3737 - 3745. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Tsai and J. M. O'Brien The Future Promise and the Current Reality of Genetic Prognostication in Patients With Uveal Melanoma Arch Ophthalmol, March 1, 2008; 126(3): 413 - 415. [Full Text] [PDF] |
||||
![]() |
J. P. Ehlers, L. Worley, M. D. Onken, and J. W. Harbour Integrative Genomic Analysis of Aneuploidy in Uveal Melanoma Clin. Cancer Res., January 1, 2008; 14(1): 115 - 122. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. D Singh, K. Sisley, Y. Xu, J. Li, P. Faber, S. J Plummer, H. S Mudhar, I. G Rennie, P. M Kessler, G. Casey, et al. Reduced expression of autotaxin predicts survival in uveal melanoma Br. J. Ophthalmol., October 1, 2007; 91(10): 1385 - 1392. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. W. Harbour Molecular Prognostic Testing in Uveal Melanoma: Has It Finally Come of Age? Arch Ophthalmol, August 1, 2007; 125(8): 1122 - 1123. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |