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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 Departments of Clinical and Anatomic Pathology, 2 General Surgery-Breast Center, and 3 Hematology and Oncology, and 4 Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio; 5 Roswell Park Cancer Research Institute, Buffalo, New York; and 6 Department of Pathology and Comprehensive Cancer Center, The University of Alabama, Birmingham, Alabama
Requests for reprints: Graham Casey, Department of Cancer Biology, ND50, Lerner Research Institute, Cleveland Clinic Lerner College of Medicine, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. Phone: 216-445-9754; Fax: 216-445-0610; E-mail: caseyg{at}ccf.org.
| Abstract |
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Experimental Design: A tissue microarray immunohistochemical analysis was done on tumors of 238 newly diagnosed breast cancer patients who underwent surgery at the Cleveland Clinic between January 1, 1995 and December 31, 1996, and a comparison was made with 5-year clinical follow-up data. Genomic copy number changes were determined by array-based comparative genomic hybridization in 47 breast cancer cases from this population and compared with BRMS1 staining.
Results: BRMS1 protein expression was lost in nearly 25% of cases. Patients with tumors that were PR negative (P = 0.006) or HER2 positive (P = 0.039) and <50 years old at diagnosis (P = 0.02) were more likely to be BRMS1 negative. No overall correlation between BRMS1 staining and disease-free survival was observed. A significant correlation, however, was seen between loss of BRMS1 protein expression and reduced disease-free survival when stratified by either loss of ER (P = 0.008) or PR (P = 0.029) or HER2 overexpression (P = 0.026). Overall, there was poor correlation between BRMS1 protein staining and copy number status.
Conclusions: These data suggest a mechanistic relationship between BRMS1 expression, hormone receptor status, and HER2 growth factor. BRMS1 staining could potentially be used in patient stratification in conjunction with other prognostic markers. Further, mechanisms other than genomic deletion account for loss of BRMS1 gene expression in breast tumors.
B signaling, suggesting specific mechanisms by which BRMS1 may regulate genes involved in the metastatic process (8, 9). Despite the potential importance of BRMS1 as a determinant of metastasis in the clinical setting, the study of patient samples from human breast cancer has been hampered by the lack of antibodies to native BRMS1 (6). The recent development of suitable antibodies to BRMS1 now makes it possible to study primary breast cancer specimens for protein expression.
In the present study, we examined BRMS1 expression by immunohistochemistry in a cohort of 238 breast cancer patients with 5-year clinical follow-up, as well as differential genomic gains and losses in a subset of cases from this series using array-based comparative genomic hybridization (aCGH). Our data revealed a strong correlation between loss of BRMS1 protein expression and reduced disease-free survival in subsets of breast cancer patients when stratified by hormone receptor [estrogen receptor (ER) and progesterone receptor (PR)] or HER2 expression status. Our results also revealed that loss of BRMS1 protein expression did not correlate with genomic deletion using aCGH, suggesting that mechanisms other than genomic deletion account for loss of BRMS1 expression in tumors.
| Materials and Methods |
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Immunohistochemistry. BRMS1 expression was assessed by immunohistochemistry of the breast cancer tissue microarray series as well as on a subset (21 of 47) of cases submitted for aCGH using a monoclonal antibody (clone 3a1.21) developed by the University of Alabama, Birmingham Cancer Center Antibody Core Facility using full-length BRMS1 as an antigen. The specificity of the antibody was confirmed by identification of appropriately sized bands in immunoblots, and by immunoprecipitation, matrix-assisted laser desorption/ionization-time of flight, and electrospray sequencing (electrospray ionization mass spectrometry-mass spectrometry) of immunoprecipitated BRMS1 to verify that the sequences were BRMS1 specific (data not shown). Briefly, 4-µm-thick unstained sections were placed onto electrostatically charged glass slides and baked overnight. Optimal primary antibody incubation and concentration (1/50) were previously determined via serial dilutions on positive control tissue (placenta). Antigen detection was done with a peroxidase-conjugated secondary antibody/3,3'-diaminobenzidine chromogen step. BRMS1 staining was scored on a 0 to 3+ intensity scale (0, negative nuclear staining; 1+, weak nuclear staining; 2+, moderately intense staining; and 3+, strong staining) by two independent observers blinded to the clinical data, and the results were entered into the research database. Results from the two independent observers were highly concordant with discordant results resolved through agreement. An individual case was considered to be positive if at least one of the two tissue cores contained sufficient tumor for evaluation and at least 10% of invasive tumor cells showed staining. Immunostaining for ER, PR, and HER2 was done as previously published (10).
aCGH. Forty-seven early-stage (I and II) frozen breast tumor samples from 22 patients with early recurrence (<60 months) and 25 age-matched patients who remained disease-free at least 70 months postdiagnosis were analyzed using aCGH. Extracted DNA was quantified and then analyzed on a 5,520 RPCI-11 BAC array containing representative segments from all major chromosome regions (Roswell Park Cancer Institute, Buffalo, NY). Genomic data were standardized and those BAC clones >1.75 or <1.75 of the mean average deviation of the data set were considered as amplified or deleted, respectively.
Statistics. Comparative bivariate statistics was done using
2 analysis (BRMS1 staining versus ER staining, PR staining, HER2 status, age >50 years, nodal status, and Bloom-Richardson grade). Survival data were available for 212 of the cases on the tissue microarray and were calculated using the generation of Kaplan-Meier curves. All statistics were carried out using SPSS software (SPSS, Inc., Chicago, IL). Statistical significance was assumed if P < 0.05. Mean follow-up of the study population was 67 months (1-106 months).
| Results |
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When looking specifically at triple negative (ER, PR, and HER) tumors, we did not observe any effect of loss of BRMS1 expression on cumulative disease-free survival (BRMS1+, 67% disease-free survival; BRMS1, 60% disease-free survival; P = 0.607). However, this subgroup only consisted of 29 patients and the relationship between BRMS1 expression and disease-free survival in cases with triple negative disease remains unclear.
Loss of BRMS1 expression is associated with HER2 protein overexpression. The relationship between hormone receptor status, BRMS1 status, and HER2 status is shown in Table 4 . The cases that were ER/BRMS1 and PR/BRMS1 showed the highest percentage of tumors that were HER2 positive compared with all of the other subgroups: 5 of 17 (29%) HER2+ of ER/BRMS1 and 8 of 32 (25%) HER2+ of PR/BRMS1, respectively. However, it should be noted that for the ER group, there was not a substantial difference in HER2 positivity between the BRMS1+ (9 of 33, 27%) and BRMS1 (5 of 17, 29%) subgroups. For ER+ breast cancers, 9 of 145 (6%) of the BRMS1+ cases were HER2 positive whereas 7 of 42 (17%) of BRMS1 tumors were HER2 positive. For PR+ breast tumors, this trend was also observed, and 7 of 117 (6%) of the BRMS1+ cases were HER2 positive whereas 4 of 27 (15%) of BRMS1 tumors were HER2 positive (P = 0.01).
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A subset of the 47 cases (23 of 47) was also analyzed for BRMS1 expression using immunohistochemistry (Table 5 ). There was moderate to strong nuclear staining (2-3+) in 13 of 23 (56%) of cases and absent to weak staining in 10 of 23 (44%) of cases. There was no statistically significant association overall between BRMS1 protein expression and BRMS1 copy number status (P = 0.316). However, note that whereas BRMS1 expression was generally independent of BRMS1 copy number status, the two cases with BRMS1 genomic deletion failed to show any expression of the BRMS1 protein, and six of the seven cases that showed amplification of BRMS1 were either 2+ or 3+ BRMS1 immunohistochemistry positive. These data imply that genomic status of BRMS1 may influence BRMS1 staining, but that, overall, there is poor correlation between copy number status and BRMS1 staining.
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| Discussion |
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A significant increase in the number of cases staining negative for BRMS1 was also seen in the subgroup diagnosed at age <50 years (P = 0.02), suggesting that BRMS1 status may be a more important predictor of clinical outcome in women developing premenopausal breast cancer. Breast cancers that present at a younger age are more likely to be hormone receptor negative, overexpress HER2, and follow a more aggressive clinical course of disease (1114). Given the fact that loss of BRMS1 in ER-negative, PR-negative, and HER2-positive tumors was associated with the lowest disease-free survival, our data suggest that BRMS1 expression may play a role in mediating the biological and clinical behavior of these subsets of tumors.
Recent reports have suggested that the ER+/PR phenotype in breast cancer may represent a biologically and clinically distinct subset of tumors compared with ER+/PR+ tumors, both in terms of worse clinical outcome and resistance to antiestrogen therapy (15, 16). Tamoxifen-treated patients with ER+/PR tumors had a significantly worse outcome if their tumors also overexpressed HER1 or HER2, compared with those that showed normal HER1 or HER2 expression. A number of other clinical studies have also reported that HER2 overexpression is associated with decreased benefit from adjuvant tamoxifen treatments (1719). It has been proposed that PR status may reflect activated HER1/HER2 growth factor signaling in these tumors, and that loss of PR in ER+ breast cancer may represent a surrogate marker for increased growth factor tyrosine kinase activity (15). The correlation between BRMS1 expression and ER and PR expression and the inverse correlation with HER2 expression in the present study suggest a role for BRMS1 in this relationship.
In the current study, those cases that were ER or PR were more likely to show HER2 overexpression and a lower disease-free survival, but they were also more likely to show a loss of BRMS1 protein. The PR, HER2+ breast cancer phenotype was the most likely to show loss of BRMS1 protein by immunohistochemistry. In fact, examination of cases in the current study showed that even in ER+ tumors, the loss of BRMS1 was associated with a higher percentage of cases with HER2 overexpression (BRMS1+, 6%; BRMS1, 17%; Table 4). In addition, for both PR+ and PR tumors, the loss of BRMS1 expression was associated with a significantly higher percentage of HER2-overexpressing breast cancer cases (Table 4). Therefore, it is interesting to speculate on a potential role for the loss of BRMS1 expression as a further modulator of the more aggressive clinical behavior of this subset of tumors. These data suggest that BRMS1 expression further stratifies PR subgroups of breast cancers, possibly in part through regulation of HER family members themselves or through modulation of HER growth factor receptor signaling. However, additional studies will be needed to define the role of BRMS1 in this context.
In this study, loss of BRMS1 expression did not correlate with nodal status. That no correlation was seen may imply that BRMS1 plays a different role in regional and distant metastases. It should be noted that whereas the presence of lymph node metastasis is associated with a worse outcome, this is not a perfect correlation. For example, in a recent study, 29% of patients with >10 positive lymph nodes had not recurred after 10 years of follow-up (20). The likelihood of recurrence correlated with gene expression, but it was unclear if BRMS1 was examined in this study. Thus, among patients with lymph node metastasis, there is biological heterogeneity in terms of who might recur and develop distant metastasis, and the role for BRMS1 in nodal disease remains to be defined.
A recent study examining BRMS1 mRNA expression in human breast cancer clinical samples failed to show any correlation between BRMS1 expression and variables of local dissemination such as tumor size and lymph node metastasis (21). However, in the present study, we found that BRMS1 protein was expressed in all normal mammary epithelia and in unaffected breast tissues from patients with cancer as well as in host inflammatory cells. The immunolocalization of BRMS1 protein was exclusively within the nucleus of both normal and tumor epithelial cells, which is in agreement with the putative role for BRMS1 as a transcription factor (1, 6, 7). Therefore, the measurement of BRMS1 mRNA levels in nonmicrodissected clinical samples could potentially be confounded by the expression of the BRMS1 gene by normal host cells within tumor tissue. Further studies will be needed to clarify this issue.
The mechanism underlying loss of BRMS1 expression in cancer cells is not known. Whereas no mutations in BRMS1 have been reported to date, BRMS1 maps to chromosome 11q13.1-11q13.2, a region that exhibits frequent genomic amplification or deletion associated with breast cancer progression (1). To examine the relationship between genomic copy number changes and BRMS1 protein expression, we did aCGH in a subset of the cases enrolled in this study and compared these data with BRMS1 protein expression. Within this subset of cases, there was some correlation between BRMS1 staining and genomic loss or gain, but for those cases showing no copy number changes, 7 of 14 (50%) showed low to no staining whereas 50% showed high BRMS1 staining. These data imply that genomic status of BRMS1 may influence BRMS1 staining, but that, overall, there is poor correlation between copy number status and BRMS1 staining. These findings suggest that an alternative mechanism, such as epigenetic promoter hypermethylation, may explain loss of BRMS1 protein expression in many of these tumors. Amplification of this region was found in approximately one third of tumors, suggesting that other genes located in proximity to BRMS1 on chromosome 11 may also be involved in breast cancer progression.
A major challenge in the treatment of breast cancer is to identify those patients that are more likely to develop metastases so that appropriate treatment can be provided. Although survival is best correlated with regional lymph node status, other differentially expressed markers in the primary tumor are also imperfectly predictive. In this study, we show that loss of BRMS1 expression is associated with decreased disease-free survival in the context of hormone receptornegative tumors. We also show a correlation between loss of BRMS1 and HER2 overexpression, suggesting a possible mechanistic relationship between BRMS1 and HER2 growth factor signaling that may have potential implications for therapeutic intervention. These data suggest that BRMS1 staining could potentially be used in conjunction with other prognostic markers for patient stratification.
| 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.
Received 3/16/06; revised 7/25/06; accepted 9/ 5/06.
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B activity. Cancer Res 2005;65:358695.This article has been cited by other articles:
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D. R. Welch Metastasis Suppressors: Discovery, Mechanisms, and Translation into Clinical Practice Am. Assoc. Cancer Res. Educ. Book, April 18, 2009; 2009(1): 191 - 195. [Full Text] [PDF] |
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