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Molecular Oncology, Markers, Clinical Correlates |
1 Departments of Pathology and 2 Hematology and Oncology, University of Regensburg, Regensburg, Germany; 3 Institute of Pathology and Anatomy, Regensburg, Germany; 4 Institute of Pathology, Klinikum Kassel, Kassel, Germany; 5 Department of Pathology, University of Vermont College of Medicine, Burlington, Vermont; and 6 Institute of Pathology, University of Basel, Basel, Switzerland
| ABSTRACT |
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Experimental Design: Thirty-nine patients with breast cancer and extensive lymph node (level III) and/or systemic metastases from a prospective single-center study of sequential HDCT/ASCT were studied. Microsatellite analysis was performed after laser microdissection using 15 markers selected for sensitive detection of microsatellite instability (MSI) in breast cancer. Exons 59 of the P53 gene were directly sequenced. Expression of P53, HER-2/neu, and the mismatch repair proteins hMSH2 and hMLH1 was evaluated by immunohistochemistry.
Results: MSI of at least three markers was detected in 13 of 39 patients (33%) and was predominantly found at tetranucleotide markers. All MSI-positive tumors showed normal expression of hMSH2 and hMLH1. Complete sequence analysis of exons 59 of the P53gene was successful in 34 cases; 18% (n = 6) revealed a mutation. Overexpression of HER-2/neu and P53 was observed in 7 (22%) and 12 (46%) of 26 evaluated cases, respectively. The presence of MSI strongly correlated with shorter overall survival (OS; P = 0.0004) and progression-free survival (PFS; P = 0.02). None of the other investigated clinical or molecular factors correlated with OS in univariate analyses, with the exception of menopausal status and previous adjuvant chemotherapy. Testing various multivariate Cox regression models, MSI remained a highly significant, independent, and adverse risk factor for OS.
Conclusions: MSI is frequent in advanced breast cancer and could be an indicator of chemotherapy resistance and poor prognosis in breast cancer patients treated with HDCT/ASCT.
| INTRODUCTION |
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There are also no definitive prognostic makers for patient outcome in HDCT/ASCT. Identifying such markers could facilitate the definition of a subgroup of patients with advanced breast cancer that will most likely respond to this aggressive treatment. A plethora of molecular markers are currently evaluated in the treatment of breast cancer, but none of these markers are routinely used in clinical practice (2) . Accepted prognostic factors for patients with metastatic breast cancer undergoing standard therapy regimens are hormone receptor status (estrogen receptor and progesterone receptor), menopausal status, localization of metastases, interval between initial diagnosis and appearance of metastases, and response to chemotherapy. On the basis of these clinical findings, Possinger et al. (3) have developed a prognostic score to classify patients with metastatic breast cancer into three different risk groups (high, intermediate, and low): metastatic pattern, receptor status, and disease-free survival were considered qualitative parameters. Combining these parameters provides a reliable indicator of tumor progression, but more precise prognostic factors are needed that reflect both the phenotype and the genetic alterations of the tumor. Standardized molecular analyses might help to select patients who would benefit from differential chemotherapeutic approaches. The cohort designated "chemoresistant" could then be offered alternative therapy modalities, which in turn could be derived from molecular characteristics of the tumor.
The aim of this study was to define molecular alterations that could predict treatment response and/or clinical outcome of breast cancer patients undergoing HDCT/ASCT.
| MATERIALS AND METHODS |
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DNA Isolation.
For molecular analysis, normal and tumor DNA was extracted using the QIAamp DNA Mini Kit (Qiagen, Hilden, Germany) according to the manufacturers specifications. Elution with 2 x 100 µl of 70°C preheated water was performed to increase yield. Each elution step included a 5-min incubation of the QIAamp spin column with the preheated water at 70°C before centrifugation. PCR template concentration was additionally increased by reducing the elution volume to 50 µl (SpeedVac SC110; Savant, Farmingdale, NY) and by performing an improved primer extension preamplification PCR (whole genome amplification) as described previously (8)
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Microsatellite Analysis.
Fifteen microsatellite markers on chromosomes 1, 2, 4, 5, 6, 11, 17, 18, 19, and 21 were selected for sensitive detection of microsatellite instability (MSI) in breast cancer according to literature review. Characteristics of microsatellite primers have been reported previously (6)
. PCR amplification reactions were performed using 50 ng of purified genomic DNA in a final volume of 20 µl in a MJ Research Thermocycler (PRC100; MJ Research, Watertown, MA; Ref. 9
). PCR products were subsequently analyzed by 6.7% polyacrylamide/50% urea gel electrophoresis (1 h, 1500 V, 55°C) in a SequiGen sequencing gel chamber (Bio-Rad, Hercules, CA) followed by silver nitrate staining as described previously (10)
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MSI was defined as the presence of novel bands after PCR amplification of tumor DNA that were not present in PCR products of the corresponding normal DNA. All gels were evaluated independently by three different investigators (P. J. W., W. D., and A. H). According to recommendations of the 1997 Bethesda Consensus Conference (11)
, MSI was diagnosed if at least 3 of 15 markers (
20%) were unstable, samples with instability in only one or two markers were classified as MSI low. Microsatellite-stable samples (MSS) did not show instability in any of the investigated markers. Loss of heterozygosity was defined as a decrease in signal intensity of the tumor sample allele to at least 50% relative to the matched normal DNA allele. Chromosomal instability (CIN) was assumed if at least 40% (
6 of 15 investigated markers) revealed loss of heterozygosity. All samples testing positive for MSI or loss of heterozygosity were reevaluated twice to exclude the possibility of false-positive results because of preferential monoallelic PCR amplification (8)
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P53Mutations.
Exons 59 of the P53tumor suppressor gene were directly sequenced in 34 tumors; the methodology has been described in detail previously (12)
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Immunohistochemistry.
Expression analyses of the mismatch repair proteins hMSH2 (n = 25) and hMLH1 (n = 26) were performed as described previously (13)
. Immunohistochemical studies for the expression of P53 (n = 26) and HER-2/neu (n = 26) used an avidin-biotin peroxidase method with a 3,3'-diaminobenzidine chromatogen. After antigen retrieval (microwave oven for 30 min at 250 W), immunohistochemistry was carried out in a NEXES immunostainer (Ventana, Tucson, AZ) following manufacturers instructions. The following antibodies were used: P53 (mouse monoclonal Bp53-12, Santa Cruz Biotechnology, Inc., Santa Cruz, CA; dilution 1:1000) and HER-2/neu (rabbit polyclonal A0485, DAKO, Glostrup, Denmark; dilution 1:400). One histopathologist performed a blinded immunohistochemical evaluation (A. H.), without knowledge of the molecular data. P53 positivity was defined as strong nuclear staining in at least 10% of the tumor cells. HER-2/neu expression was scored according to the DAKO HercepTest (14)
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Possinger Score.
Metastatic pattern, hormone receptor status and disease-free survival before HDCT/ASCT were scored quantitatively as previously described by Possinger et al. (3)
, assigning each patient to one of three different risk groups: high, intermediate, or low.
Statistical Analyses.
Differences were considered statistically significant when Ps were <0.05. A statistical correlation between clinicopathological and molecular parameters was tested, using a two-sided Fishers exact test. A logistic regression was performed to study the correlation between age and categorical variables. Progression-free survival (PFS) and overall survival (OS) time were calculated according to the Kaplan-Meier survival curves (15)
. PFS and OS were measured from the start of HDCT and compared between women with or without any of the clinical, pathological, or molecular risk factors by two-sided log-rank statistics (16)
. A stepwise multivariable Cox regression model (17)
was adjusted, testing the independent prognostic relevance of MSI. The limit for reverse selection procedures was P = 0.2. The proportionality assumption for all variables was assessed with log-negative-log survival distribution functions. The characteristics of all variables are shown in Table 2
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| RESULTS |
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HDCT/ASCT.
Patients were followed for a median of 24.4 months. Of 39 patients, 4 (10%) achieved at least a partial remission, 22 patients (56%) were in complete remission after HDCT. Mean OS time was 40.1 months with a 95% confidence interval (CI) of 33.6746.45. The median OS time could not be reached; at the qualifying date (March 1, 2000) 26 patients (67%) were still alive. No therapy-associated deaths were observed, but 2 patients progressed rapidly (Nos. 17 and 39). Mean and median PFS was 21.6 and 13.2 months, respectively. The 2-year survival rates and 95% CIs concerning PFS and OS were 0.23 (0.0990.363) and 0.54 (0.3820.695).
Possinger Score.
Applying the Possinger score for metastatic breast cancer (3)
, 12 patients (31%) were estimated to have a poor prognosis, another 12 patients to have an intermediate prognosis, and the remaining 15 patients (38%) were considered to have a favorable prognosis. However, PFS and OS were not significantly different between the three groups.
Descriptive and Univariate Analyses.
For descriptive data analysis, all relevant variables were correlated with the MSI status (Table 2)
, but no significant association was seen. Cases showing MSI (
3 of 15 markers) were compared with microsatellite stable (MSS and MSI low) cases regarding PFS and OS by univariate log-rank statistics. MSI was highly associated with shorter PFS (P = 0.02) and OS (P = 0.0004; Figs. 1, A and B
). Microsatellite stable cases (MSS and MSI low) had a median PFS of 28.4 months compared with 2.5 months in patients with MSI tumors. Median OS for MSI-positive cases was 22.3 months, whereas the median OS time for patients with MSS and low MSI could not be estimated because <50% of patients died within the time of follow-up. Initial tumor size (P = 0.008) and a history of adjuvant chemotherapy (P = 0.003) were the only other variables which correlated significantly with PFS. Menopausal status (P = 0.04) and previous standard adjuvant chemotherapy (P = 0.02) were associated with shorter OS. None of the other clinical, pathological, or molecular factors correlated significantly with OS (Table 2)
. Interestingly, younger patients showed a tendency to have microsatellite unstable tumors (P = 0.07; odds ratio = 1.11; 95% CI, 0.991.23).
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Subsequently, the trichotomous variables age at diagnosis and Possinger score were dichotomized by the introduction of dummy variables (AGEDUM1, AGEDUM2, POSSDUM1, and POSSDUM2). Again, only MSI was significant in the global model. After reverse selection, AGEDUM1, CIN, and MSI (P = 0.0009; hazard ratio = 10.10; 95% CI, 2.5739.68) remained in the model.
Finally, multiplicative terms of interaction (INTER16) were considered, representing interactions between MSI and dichotomous covariables. Because of the multitude of variables compared with the small number of cases, interpretation was difficult. The global model included POSSDUM2, INTER3, and INTER6 as significant variables. After reverse selection, a model containing MSI, AGEDUM1, POSSDUM2, INTER3, and INTER6 was found (P < 0.01).
Assuming different model constructs, the following conclusions can be drawn: (a) MSI was a prognostic factor for the OS probability of advanced breast cancer patients undergoing HDCT/ASCT; (b) other factors were relevant as well, particularly age at diagnosis (
40 years) and Possinger score (score = 3 versus score = 1); and (c) potential interactions between the MSI status and OS were influenced by CIN and Possinger score (score = 3 versus score = 1).
| DISCUSSION |
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3 of 15 markers unstable) in 33% (13 of 39) of cases, a frequency that is comparatively high. Possible explanations would include the use of laser-assisted tissue microdissection (6)
and a selection of a sensitive MSI marker panel, but the highly selected patient cohort with advanced breast cancers remains a strong potential bias. In colorectal cancer, MSI was shown to be independently predictive of a relatively favorable patient outcome (24) , reduced likelihood of metastases (25) , and better survival after adjuvant chemotherapy with fluorouracil-based regimens (26) . However, Ribic et al. (27) have recently shown that adjuvant chemotherapy with fluorouracil benefited patients with colon tumors exhibiting CIN but not those with tumors exhibiting MSI. The data suggest that fluorouracil-based adjuvant therapy actually decreased the rate of survival among patients with tumors showing MSI. This is apparently an inconsistent finding in view of the fact that colon carcinomas with MSI were associated with an overall better survival than those with CIN. Patients with colorectal cancers that exhibit high-frequency MSI have longer survival than stage-matched patients with cancers revealing MSI (24 , 26) .
Several groups have reported a poorer prognosis for MSI-positive breast carcinomas (28, 29, 30, 31) , but MSI has never been correlated with patient outcome in HDCT studies. Testing various multivariate Cox regression models, we could demonstrate that MSI is a highly significant, independent, and adverse risk factor for OS of breast cancer patients receiving HDCT/ASCT with a 7-fold increase in the relative risk of tumor-related death. MSI of the primary tumor is the most significant prognostic factor characterized in HDCT/ASCT studies thus far. On the analogy of Ribic et al. (27) for colon cancer, HDCT/ASCT was only beneficial for breast cancer patients exhibiting microsatellite stability or low instability (<3 of 15 markers). As expected for advanced tumor stages, lymph node status was of less prognostic importance for OS (P = 0.2) and was excluded from subsequent multivariate analyses. Event rates for tumor progression and tumor-related death were too small to meet the proportional hazards assumption regarding lymph node status.
There is growing evidence that MSI in breast cancer patients may represent a type of genetic instability different from that seen in colorectal cancer. All 13 MSI-positive breast tumors in our study showed normal expression of the mismatch repair proteins hMSH2 and hMLH1. Lack of MSI in breast cancers occurring in nonpolyposis colorectal cancer families has led to the exclusion of breast cancer as an integral tumor of the nonpolyposis colorectal cancer syndrome (32) . MSI in breast cancer has typically been found in tri- and tetranucleotide repeats in this and other studies (30 , 33 , 34) . In contrast, diagnosis of nonpolyposis colorectal cancer-associated replication errors is most easily determined by examination of a panel of simple mononucleotide (BAT25and BAT26) and dinucleotide (D5S346, D17S250, and D2S123) repeat sequences (11) . A pattern of MSI similar to that found in the current study has been detected in non-small cell lung cancer, termed elevated MSI at selected tetranucleotide markers (35) . This type of MSI was associated with P53mutations and displayed a phenotype inconsistent with defects in mismatch repair pathways. Similar to studies by Ahrendt et al. (35) , our series of breast cancers revealed MSI predominantly in tetranucleotide repeats. Eighty-five percent of all MSI-positive tumors were unstable in at least one of the five tested tetranucleotide markers, but the mechanism causing these alterations still remains unclear.
In a randomized trial of HDCT in patients with operable breast cancer and extensive lymph node involvement with a median follow-up of 6.9 years, both the number of tumor-positive axillary lymph nodes after induction chemotherapy and the clinical T-stage before chemotherapy were significant factors for OS (36) . Numerous novel molecular variables have been proposed as putative prognostic factors in breast cancer (2) . However, only few studies investigated molecular alterations in the primary tumor in patients receiving HDCT/ASCT. In a cytogenetic analysis of 34 patients with lymph node-positive, high-risk breast cancer treated with HDCT/ASCT using comparative genomic hybridization, Climent et al. (37) showed that genomic loss of chromosome arm 18p predicted an adverse clinical outcome with shorter PFS.
Data on the importance of P53alterations as a predictor of poor outcome and chemoresistance in breast cancer are controversial (38) , probably as a result of heterogeneity of studied patient cohorts and chemotherapeutic regimens, the different methods of assessing response (clinically versus histologically), and variations in the methods used to determine the P53status. In several studies, mutations in the P53gene correlated independently with poor patient outcome in breast cancer (20 , 39 , 40) , likely reflecting an increased proliferative capacity of P53-mutant tumor cells and the greater resistance of such cells to the induction of apoptosis by a variety of chemotherapeutic agents (39) . In a study of 149 high-risk primary breast cancer patients undergoing HDCT/ASCT, P53has been shown to be the strongest predictor of survival with a relative risk of 6.06 (41) . However, in vitro results of an association of P53mutation and chemoresistance failed to translate into a significant correlation between immunohistochemically detected overexpression of P53 protein and clinical response to therapy in breast cancer patients (42 , 43) . Thus, the effect of P53mutations on the sensitivity of breast cancer to genotoxic drugs has been disputed. In high-grade, locally advanced breast cancers, inactivation of the P53pathway seemed to improve the response to HDCT (six cycles of 75 mg/m2 epirubicin and 1200 mg/m2 cyclophosphamide), whereas initial P53status and histological tumor response were strongly associated (P = 0.0001; Ref. 39 ).
HER-2/neu overexpression may represent yet another independent negative prognostic factor for patients with metastatic breast cancer who undergo HDCT/ASCT; two studies reported an association of Her-2/neu overexpression with generally shorter PFS and OS (44 , 45) . On the basis of these data, Nieto et al. (46) have proposed a prognostic model for relapse after HDCT in which HER-2/neu overexpression, number of tumor sites, and primary nodal ratio were independent predictors of long-term outcome (median follow-up 62 months) for stage IV oligometastatic breast cancer. In the present study, however, neither P53 nor HER-2/neu alterations correlated significantly with patient survival.
In summary, we demonstrated an independent negative correlation between MSI in the primary tumor and OS in advanced breast cancer patients treated with HDCT/ASCT. MSI may represent a potential molecular marker to predict differential patients responses to treatment and clinical outcomes. Larger prospective studies are currently conducted to validate our findings.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Note: Data have been presented in part at the 92nd Annual Meeting of the American Association for Cancer Research, April 610, 2001, San Francisco, CA.
Requests for reprints: Arndt Hartmann, Institute of Pathology, University of Basel, Schönbeinstrasse 40, CH-4031, Basel, Switzerland. Phone: 41-61-265 2880; Fax: 41-61-265 3194; E-mail: arndt.hartmann{at}klinik.uni-regensburg.de
Received 4/14/03; revised 9/ 2/03; accepted 9/ 8/03.
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