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Departments of 1 Obstetrics and Gynecology, 2 Pathology, 3 Urology, and 4 Biostatistics and Documentation, Innsbruck Medical University, Innsbruck, Austria
Requests for reprints: Martin Widschwendter, Department of Obstetrics and Gynecology, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria. Phone: 43-512-504-81055; Fax: 43-512-504-23112; E-mail: Martin.Widschwendter{at}uibk.ac.at.
| Abstract |
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Key Words: Breast cancer Tumor markers and detection of metastasis DNA methylation/epigenetics Clinical drug resistance Molecular markers of metastasis and progression
| Introduction |
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In recent years, changes in the status of DNA methylation, known as epigenetic alterations, have turned out to be one of the most common molecular alterations in human neoplasia including breast cancer (5). In addition, numerous studies have shown tumor-specific alterations in DNA recovered from plasma or serum of patients with various malignancies, a finding that has potential for molecular diagnosis and prognosis (610). Very recently, we were able to detect a prognostic value for APC and RASSF1A methylation in pretherapeutic sera of patients with breast cancer (11). RASSF1A DNA methylation has consistently been shown to be a prognostic marker in patients who did not receive adjuvant therapy (11).
This study now shows that methylated RASSF1A DNA in serum is a surrogate marker for circulating breast cancer cells and that this cancer-specific DNA alteration allows monitoring of adjuvant therapy in patients with cancer: Disappearance of RASSF1A DNA methylation in serum throughout treatment with tamoxifen indicates a response, whereas persistence or new appearance means resistance to adjuvant tamoxifen treatment.
| Materials and Methods |
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Serum Samples, DNA Isolation, and MethyLight Analysis. Patients' blood samples were drawn before or 1 year after therapeutic intervention. Blood was centrifuged at 2,000 x g for 10 minutes at room temperature, and 1-mL aliquots of serum samples were stored at 30°C.
DNA isolation, bisulfite modification, and MethyLight analysis was done as described recently (11).
Laser Capture Microdissection. The PixCell II LCM System (Arcturus Engineering, Mountain View, CA) was used for laser capture microdissection of paraffin-embedded tissues. Ten-micrometer-thick sections of 13 breast cancer patients with a ductal carcinoma in situ were used. For each analyzed fraction, 1,000 cells were "laser captured". DNA extraction was carried out using the Arcturus Pico Pure DNA extraction kit according to the manufacturers' instructions. DNA bisulfite modification and MethyLight analysis was done as described (11).
Statistics. We used Pearson's
2 or, in the case of low frequencies per cell, Fisher's exact method to test associations between categorically clinicopathologic features and methylation measures. The Mann-Whitney U test was used to assess differences between nonparametric distributed variables. Relapse-free and overall survival were calculated from the date of second serum draw (1 year after diagnosis) to the date of relapse or death or last follow-up. Relapse-free and overall survival curves were calculated with the Kaplan-Meier method. Univariate analysis of overall survival according to clinicopathologic factors [tumor stage, grading, nodal status, menopausal status, and hormone receptor status (estrogen and/or progesterone receptor positivity)], and pretherapeutic and 1-year-after serum RASSF1A DNA methylation was done using a two-sided log rank test.
Multivariate Cox proportional hazards analysis was used to estimate the predictive effect of methylated serum RASSF1A DNA.
A P value <0.05 was considered a statistically significant difference. All statistical analyses were done using SPSS Software 10.0 (Chicago, IL).
| Results |
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To determine whether RASSF1A DNA methylation acts as a DNA-based marker solely for breast cancer cells but not for other breast- and/or tumor-associated cells, we did laser-assisted microdissection of 13 paraffin-embedded specimens that had been removed due to hormone receptorpositive carcinoma in situ. RASSF1A methylation was detected in all cancer cell fractions, whereas most of the underlying stroma, the nonneoplastic breast epithelium, or the adjacent stroma were negative for RASSF1A methylation (Fig. 1).
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RASSF1A DNA Methylation in Serum of Patients with Primary Breast Cancer Who Received Adjuvant Tamoxifen Treatment. In this retrospective approach we used prospectively collected serum samples from patients who received tamoxifen for adjuvant treatment due to primary nonmetastatic breast cancer, who had pretherapeutic as well as serum samples drawn 1 year after diagnosis (i.e., >6 months after start of tamoxifen therapy) and who showed no relapse within the first year after diagnosis or at second serum draw. A total of 19.6% and 22.3% of patients showed RASSF1A DNA methylation in their pretherapeutic and 1-year-after serum samples, respectively. Pretherapeutic RASSF1A methylation showed nearly the same associations with clinicopathologic parameters as described earlier for a different set of patients (11) and was correlated with tumor size, menopausal status (Supplementary Data), and age [median age: RASSF1A unmethylated (59.7 years; range, 36.9-88.4); RASSF1A methylated (67.6 years; range, 45.8-85.3; P = 0.006)]. RASSF1A DNA methylation at second serum draw after 1 year (Supplementary Data) was associated only with age [median age: RASSF1A unmethylated (61.3 years; range, 37.8-86.1); RASSF1A methylated (67.4 years; range, 45.2-89.6; P = 0.047)].
Prognostic Significance of Clinicopathologic Features and Pretherapeutic RASSF1A DNA Methylation in Serum. Tumor size as well as lymph node metastasis were poor prognostic parameters for relapse-free as well as for overall survival, whereas tumor grade had a statistically significant effect on relapse-free survival (Table 1A and B). Neither menopausal status, hormone receptor status, nor pretherapeutic RASSF1A DNA methylation in serum had an impact on prognosis (Table 1A and B).
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Neg" and "Finally Pos" groups, respectively (Fig. 2). With regard to survival, no statistically significant difference between the "Pos
Neg" and "Always Neg" groups was observed (Fig. 2).
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| Discussion |
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During recent years, some studies have reported cell-free DNA in serum/plasma of patients with breast cancer at diagnosis (7, 11, 13, 14). This article shows that RASSF1A DNA methylation is present in nearly all breast cancer cells and is rare in serum of patients with nonneoplastic breast conditions or patients with other invasive cancers, such as cervical cancer. Recently, RASSF1A methylation was reported to never be observed in serum of noncancer patients (9, 10). This slightly discrepant finding may be because we studied a highly selected group of patients who had either a cervical cancer (and 4 of 5 patients with RASSF1A methylation in their serum had advanced disease) or a nonneoplastic lesion of the breast, conditions that are associated with a higher lifetime risk of developing breast cancer (15), especially in the age group of patients who showed RASSF1A methylation in their serum. In light of these data, we speculate that our "false-positive" controls may indicate cancer predisposition or a cancer not yet evident clinically.
We assume that serum RASSF1A DNA methylation is a surrogate marker for circulating breast cancer cells and disappearance indicates a response, whereas persistence or reappearance means resistance to adjuvant tamoxifen treatment.
Adjuvant endocrine therapy is one of the keys to improving breast cancerspecific survival. Recently, a prospective, placebo-controlled trial showed beneficial effects of the aromatase inhibitor letrozole, a drug that reduces local production of estradiol, after discontinuation of tamoxifen therapy (4). Of the 2,582 patients treated in the letrozole arm, only 29 women profited from this treatment by developing no distant metastases as compared with the placebo group. This means that 100 patients have to be treated to prevent distant metastasis in one patient. Because aromatase inhibitors are potentially harmful (e.g., osteoporosis) and cause discomfort (e.g., arthralgia, myalgia) to patients as well as giving economic strain to the health system, tools to identify patients likely to profit from this treatment are acutely needed. Serum RASSF1A DNA methylation is an easy means of detecting patients undergoing adjuvant tamoxifen treatment who need secondary adjuvant therapy. We were able to detect RASSF1A methylation in about 20% of patients with breast cancer 1 year after treatment commencement. It is plausible to speculate that only these patients will benefit from further adjuvant treatment (e.g., switch to aromatase inhibitors). The ability to detect such patients would have a great effect on cost-effectiveness and on preventing side effects in patients otherwise "overtreated" with adjuvant treatment.
In conclusion, we here describe a DNA methylationbased surrogate marker for circulating tamoxifen-resistant cells that can be easily measured in serum.
| Acknowledgments |
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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.
We thank Inge Gaugg, Lisl Perkmann, Vera Stivic, Martina Chamson, and Andrea Peyer for excellent technical assistance, and all our colleagues at the Department of Gynecology and Obstetrics in Innsbruck. This article is dedicated to my wife Maria and my son Julian (M. Widschwendter).
| Footnotes |
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Received 7/ 8/04. Revised 11/24/04. Accepted 12/ 8/04.
| References |
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