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Molecular Oncology, Markers, Clinical Correlates |
1 Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical School, Dallas, Texas; 2 Massachusetts General Hospital Biostatistics Center, Harvard Medical School, Boston, Massachusetts; 3 Department of Obstetrics and Gynecology, Saint Vincent Hospital and Catholic University of Korea, Suwon, Kyong-Ki-Do, Korea; and 4 Department of Obstetrics, Gynecology, and Reproductive Biology, Brigham and Womens Hospital, Dana Farber-Harvard Cancer Center, Boston, Massachusetts
| ABSTRACT |
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Experimental Design: Thirty-eight ovarian cancer patients had a single pretreatment blood sample and 200 postoperative specimens were prospectively collected during chemotherapy and follow-up. OPN measurements were performed using an enzyme-linked immunoassay, and CA125 levels were concurrently obtained. Wilcoxons signed rank-sum test was used to perform paired comparisons between pretreatment and postoperative OPN and CA125 measurements. Longitudinal mixed effects polynomial models were used to determine whether OPN and CA125 levels correlated with the development of recurrent ovarian cancer.
Results: The median pretreatment OPN level was 178 ng/ml (range, 123468) and the median CA125 measurement was 812 units/ml (range, 1281,500). There was a trend for OPN levels to decline after treatment was initiated (P = 0.07), but decreasing CA125 measurements were more consistently observed (P = 0.0009). The quadratic functional trends of OPN and CA125 were each highly significant (P < 0.0001). Although inferior to CA125 in predicting clinical response to therapy, OPN rose earlier in 90% (95% confidence interval, 56100%) of the patients developing recurrent disease (median lead time, 3 months).
Conclusions: OPN may be a clinically useful adjunct to CA125 in detecting recurrent ovarian cancer.
| INTRODUCTION |
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High-throughput cDNA microarray techniques offer great potential for identifying specific biomarkers of several types of cancer (8 , 9) . Numerous candidate tumor markers of ovarian cancer have been reported (10 , 11) . Recently, osteopontin (OPN) was shown to exhibit 184-fold overexpression by comparing pooled ovarian cancer cell lines to healthy human ovarian surface epithelium (12) . OPN is a secreted glycoprotein that is detectable in human body fluids. Plasma levels of this protein have been shown to correlate with disease status in several types of carcinoma (13 , 14) .
Mean OPN levels are higher (P < 0.001) in epithelial ovarian cancer patients compared with healthy controls (15) . However, this putative biomarker has not been directly compared with CA125 in monitoring patients postoperatively during treatment and follow-up. The purpose of this study was to test the hypothesis that OPN is a clinically useful adjunct to CA125 in detecting recurrent ovarian cancer.
| PATIENTS AND METHODS |
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Enzyme-Linked Immunosorbent Assay.
Levels of OPN were measured in plasma samples with a solid-phase sandwich ELISA using a commercially available kit (Code 17158, Immuno-Biological Laboratories) as described previously (15)
. Briefly, microplates were first precoated with antihuman OPN rabbit IgG [100 µl of 20 µg/ml in 0.1 M carbonate buffer (pH, 9.5)] and blocked with 1% BSA and 0.05% Tween 20. Plasma and standard OPN samples were diluted with 1% BSA and 0.05% Tween 20 in PBS and incubated for 1 h at 37°C. After seven washes with 0.05% Tween 20 in phosphate buffer, horseradish peroxidase-labeled conjugated antihuman OPN (10A16) mouse monoclonal antibody (100 µl of 2 ng/ml) was added and incubated for 30 min at 4°C. After nine washes, 100 µl of tetramethyl benzidine buffer was added, and the signal was allowed to develop for 30 min at room temperature. The reaction was stopped with 100 µl of 1 N sulfuric acid. The absorbance at 450 nm was measured by an automatic ELISA reader (Bio-Rad, Hercules, CA).
Results were converted from the mean absorbance of duplicate wells after subtraction of background values. Recombinant human OPN protein (IBL) was used as a standard. The standard curve was prepared simultaneously with the measurement of test samples. Reagent blank, test-sample blank, and internal controls of plasma samples were used to normalize OPN values obtained from each experiment.
Clinical Data Collection.
Clinical data were prospectively recorded, including patient age, race, Federation of Gynecology and Obstetrics stage, type of adenocarcinoma, histological grade, primary therapy, residual tumor after surgical cytoreduction, type of chemotherapy, CA125 level at each visit, and response to therapy and clinical outcome. All patients were followed to disease recurrence, death, or April 2003. Surviving patients had a median follow-up of 11.5 months (range, 227).
Complete response was defined by a normal physical examination, a normal computed tomographic scan of the abdomen and pelvis, and a normal serum CA125 level. The applied cutoff value for CA125 was 35 units/ml as recommended by Bast et al. (5) . A partial response was defined by a decrease of at least 50% in the sum of the largest dimensions of tumors as measured by computed tomographic scanning. A smaller decrease or any increase in tumor size during primary chemotherapy was defined as a nonresponder. The duration of overall survival was the interval between initiation of treatment (surgery or chemotherapy) and death.
Statistical Analysis.
Wilcoxons signed rank-sum test was used to perform paired comparisons between pretreatment and postoperative OPN and CA125 measurements. Longitudinal mixed effects polynomial models (quadratic functions of months after initial surgery) were used to describe the longitudinal behavior of OPN and CA125 over time. Each model allowed random intercept and random coefficients of all polynomial terms and was fit to the following two subgroups: complete clinical responders and partial/nonresponders. The Federation of Gynecology and Obstetrics stage of disease was included as the adjusting covariate.
2 or the Fishers exact test was used for dichotomous variable analysis. The level of critical significance was assigned at P < 0.05. All analyses were performed using SAS version 8.2 (SAS Institute, Cary, NC), SPSS version 9.0 (SPSS Inc., Chicago, IL), and S-PLUS (Insightful Inc., Seattle, WA).
| RESULTS |
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| DISCUSSION |
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Postoperative OPN levels decreased in 77% of patients undergoing primary cytoreductive surgery. Significantly reduced circulating plasma levels would be expected after tumor debulking if ovarian cancer cells actively secrete OPN. Microdissected ovarian tumors and cell lines have been shown to exhibit OPN mRNA overexpression. In addition, OPN protein expression is increased in ovarian carcinoma (15)
. Correlation of OPN levels and surgical outcome in the majority of patients suggests the potential clinical utility of this marker during primary treatment. Serum human kallikrein 6 (68%) and prostasin (88%) concentrations have also been reported to drop after ovarian cancer debulking, but not ß1,4-galactosyltransferase (10
, 19
, 20)
. Interestingly, one of the patients in this study with a postoperative OPN increase (Fig. 4)
had significant postsurgical residual disease and expired within 8 weeks despite a declining CA125. Although no putative marker has yet been shown to be clinically superior to CA125, OPN may be a biologically plausible adjunct to evaluate surgical response.
OPN and CA125 each declined for 69 months after ovarian cancer diagnosis, but OPN measurements were inferior to CA125 in predicting complete clinical responders. Although the combination of markers was similar to CA125 alone, our sample size may not have been sufficient to identify a clinically meaningful advantage by adding OPN. Serum levels of tissue polypeptide-specific antigen and ß1,4-galactosyltransferase have also been combined with CA125 to determine whether recurrent ovarian cancer can be detected earlier (20 , 21) . The utility of adding OPN should be prospectively evaluated in a larger prospective study (22) .
OPN measurements began rising earlier than CA125 with a median lead time of 3 months in this study. Elevations of CA125 alone have been shown to predate clinical relapse by a median of 4 months in approximately 70% of patients (23 , 24) . There is no evidence that reinstituting treatment for a rising CA125 without other evidence of recurrence will improve survival, but surgical exploration may identify a group of patients with subclinical macroscopic disease that benefit from cytoreduction at the time of lowest tumor burden (17) . A prospective randomized trial is currently underway to determine whether early institution of second-line treatment for a rising CA125 produces a survival benefit as well as an enhancement in quality of life, compared with treatment at the time of clinical or symptomatic recurrence.
OPN in blood may derive from several tissue sources and many different tumor cell types (25) . On the basis of transcriptional profiling, OPN has been proposed as the leading candidate clinical marker of colon cancer (26 , 27) . Elevated OPN concentrations are also associated with increased tumor burden and decreased survival in breast and prostate cancer (13 , 28) . Different histological subtypes of ovarian carcinoma exhibit different patterns, as follows: serous tumors appear to actively secrete OPN to psammoma bodies whereas mucinous variants exhibit high levels of OPN in the cytoplasm (15 , 29) . The apparent clinical utility of OPN in several human cancers supports our observation that this marker has potential applications during the treatment and follow-up of patients with ovarian cancer. OPN undergoes extensive posttranslational modification, and at least three transcriptional variants of OPN have been described (30) . Additional studies may define isoforms of OPN that are more unique in ovarian cancer.
| 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.
Requests for reprints: John O. Schorge, Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., J7.124, Dallas, TX 75390-9032. Phone: (214) 648-3026; Fax: (214) 648-8404; E-mail: john.schorge{at}utsouthwestern.edu
Received 10/ 7/03; revised 12/30/03; accepted 2/17/04.
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