Clinical Cancer Research The Science of Cancer Health Disparities
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
Clinical Cancer Research 13, 1405-1411, March 1, 2007. doi: 10.1158/1078-0432.CCR-06-1933
© 2007 American Association for Cancer Research
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kirkegaard, T.
Right arrow Articles by Bartlett, J. M.S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kirkegaard, T.
Right arrow Articles by Bartlett, J. M.S.

Human Cancer Biology

Amplified in Breast Cancer 1 in Human Epidermal Growth Factor Receptor–Positive Tumors of Tamoxifen-Treated Breast Cancer Patients

Tove Kirkegaard1,3, Liane M. McGlynn1, Fiona M. Campbell1, Sven Müller3, Sian M. Tovey1, Barbara Dunne2, Kirsten V. Nielsen3, Timothy G. Cooke1 and John M.S. Bartlett1

Authors' Affiliations: 1 Endocrine Cancer Group, Section of Surgical and Translational Research and 2 Department of Pathology, Glasgow University, Glasgow Royal Infirmary, Glasgow, United Kingdom and 3 DAKO Denmark A/S, Glostrup, Denmark

Requests for reprints: John M.S. Bartlett, Endocrine Cancer Group, Edinburgh Cancer Research Centre, Western General Hospital, Crewe Road South, Edinburgh EH4 2XR, United Kingdom. Phone: 131-777-3584; Fax: 131-777-3520; E-mail: John.Bartlett{at}ed.ac.uk.


   Abstract
Top
 Abstract
Materials and Methods
 Results
 Discussion
 References
 
Purpose: Amplified in breast cancer 1 (AIB1) is a member of the p160/steroid receptor coactivators family and is involved in estrogen-dependent gene transcription by reducing the antagonistic activity of tamoxifen-bound estrogen receptor-{alpha} (ER-{alpha}). The present study was carried out to test the hypothesis that AIB1 protein expression and/or gene amplification mediates tamoxifen resistance in breast cancer.

Experimental Design: Immunohistochemistry using AIB1 antibody and fluorescence in situ hybridization using probes specific for AIB1 and chromosome 20 was done on 402 ER-{alpha}–positive tamoxifen-treated breast cancers.

Results: AIB1 overexpression was not associated with relapse during treatment with tamoxifen. In contrast, high AIB1 expression in patients with human epidermal growth factor receptor (HER) 2– and HER3-overexpressing tumors or tumors expressing one or more of HER1, HER2, or HER3 (HER1-3 positive) was associated with an increased risk of relapse on tamoxifen [hazard ratio, 2.20; 95% confidence interval, 1.07-3.52 (P = 0.0416); hazard ratio, 2.42; 95% confidence interval, 1.32-4.43 (P = 0.0030), respectively]. AIB1 gene amplification was observed in 18 of 362 (5%) patients. High AIB1 gene copy number had no effect on overall or disease-free survival.

Conclusions: Data presented here support a role for AIB1 expression on relapse during tamoxifen treatment in hormone-responsive HER-expressing clinical breast cancers and support clinical evidence, suggesting a cross-talk between ER-{alpha} and growth factor receptor pathways through changes in expression of specific coactivator proteins, such as AIB1. This study highlights the potential that tumor profiling, using multiple markers of treatment response, may improve patient selection for endocrine treatment, such as tamoxifen or aromatase inhibitors.

Tamoxifen has been the standard adjuvant endocrine treatment of postmenopausal women with primary estrogen receptor (ER)-{alpha}–positive breast cancer since the 1970s. Unfortunately, some of these patients have a poor prognosis that requires more heavy treatment and approximately one fourth of tamoxifen-treated breast cancers exhibit either de novo (present before tamoxifen treatment) or acquired resistance during the course of therapy (1). Recently, alternative endocrine therapies, such as treatment with aromatase inhibitors (AI), are found to be effective after disease relapse because most patients remain ER-{alpha} positive (2). Switching therapeutic agents in the adjuvant setting is however unwarranted for many patients as ~75% of patients treated with tamoxifen remain alive and disease-free up to 15 years after treatment (3). The potential indiscriminate implementation of AIs in breast cancer underlines the need to identify the molecular mechanisms involved in development of tamoxifen resistance. The aim is ultimately to identify patients at high risk of developing tamoxifen resistance, who would derive maximum benefit from selective targeting of other drugs, such as AIs.

Estrogen-mediated tumor growth and disease progression is controlled not only by binding of estrogen to ER-{alpha} but also by posttranslational events, such as phosphorylation of ER-{alpha} and interactions between ER-{alpha} and specific coregulator proteins (4–6). In vitro studies have shown that coregulator proteins can be either coactivators, which enhance ER-{alpha}–mediated gene transcription, or corepressors, which suppress it (7, 8). In the absence of ligands, ER-{alpha}–mediated gene transcription is repressed via recruitment of corepressors. Ligand binding to ER-{alpha} triggers the release of the corepressors and subsequently recruitment of coactivators through conformational changes that expose a coactivator-binding groove on the surface of the ligand-binding domain (9). Cell line studies suggest that cross-talk between ER-{alpha} and growth factor receptor pathways contribute to endocrine resistance, at least in part, through changes in expression and activation of coactivator proteins (10). Overexpression of coactivators in the presence of ligand-bound nuclear receptor significantly increases hormone-induced gene transcription (11). Tamoxifen and other antiestrogens antagonize estrogen action by competing for binding to ER-{alpha}, resulting in conformational changes, which favor recruitment of corepressors, leading to inhibition of transcription (6, 7, 12). In this case, overexpression of coactivators can now enhance the agonistic activity of tamoxifen-bound ER-{alpha} leading to tamoxifen resistance (13, 14).

One of the best-characterized groups of ER-{alpha} coactivators is the p160/steroid receptor coactivator family consisting of steroid receptor coactivator-1, TIF-2 (GRIP1), amplified in breast cancer 1 (AIB1; steroid receptor coactivator-3, RAC3, ACTR) and p/CIP; (15–17). These have been identified as nuclear cofactors that activate the AF-2 function of hormone-bound ER-{alpha} to enhance gene transcription. AIB1 is located on chromosome 20q12, which is a frequently amplified chromosome region in breast cancer (16). The AIB1 gene is amplified in 5% to 10% and the protein overexpressed in >30% of primary breast carcinomas (15, 16, 18, 19). AIB1 amplification is preferentially found in ER-{alpha}– and progesterone receptor–positive breast tumors (18). High levels of tumor AIB1 expression has been associated with decreased risk of relapse in untreated patients. However, in tamoxifen-treated patients, AIB1 overexpression acts as a marker of disease relapse by reducing the antagonistic activity of tamoxifen-bound ER-{alpha} in breast cancer patients, leading ultimately to ineffective endocrine treatment (6).

The human epidermal growth factor receptor (HER) family of type-1 receptor tyrosine kinases consists of four members, epidermal growth factor receptor/HER1, HER2/ErbB-2, HER3/ErbB-3, and HER4/ErbB-4 (20), which regulate cellular proliferation, differentiation, and apoptosis in a growth factor–dependent manner (21–23). Previously, we have shown, in a cohort of 402 ER-positive breast cancer patients, that patients whose tumors overexpress HER2 or one or more of HER1, HER2, or HER3 had increased risk of relapse on tamoxifen (24). HER signaling is a frequent phenomenon in various human cancers (25). HERs are activated by ligand binding, which activates downstream signal transduction pathways, such as the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways. Signaling through the HER receptor pathways activates AIB1 by phosphorylation at six different phosphorylation sites (10, 26, 27).

Overexpression of AIB1 has been shown previously to mediate early relapse in patients with HER2-overexpressing tumors (6). However, as ER-{alpha}–positive tumors are more likely to be HER2 negative, the current study was carried out to extend this previous study by testing the hypothesis that gene amplification and/or protein overexpression of AIB1, especially in HER1-3–positive tumors, predicts for early relapse in tamoxifen-treated breast cancers.


   Materials and Methods
Top
 Abstract
 Materials and Methods
Results
 Discussion
 References
 
Patients. A total of 402 ER-{alpha}–positive breast carcinomas of patients diagnosed between 1983 and 1999 at Glasgow Royal Infirmary were collected retrospectively for analysis. ER-{alpha} status was determined as described previously (24). ER-{alpha} positivity was defined as 10% or more positive tumor cells staining at any intensity, in accordance with current local pathology guidelines. Ethical approval was obtained from the local ethics committee.

Immunohistochemistry. Immunohistochemistry for AIB1 (BD Transduction Laboratories, San Diego, CA) was carried out on tissue microarrays as described previously (24, 28) using a standard immunoperoxidase procedure. In brief, antigen retrieval was done by microwaving the slides under pressure for 5 min in TE buffer [1 mmol/L EDTA, 5 mmol/L Trisma base (pH 8.0)]. Endogenous peroxidase activity was quenched in 1% H2O2 for 10 min and nonspecific binding blocked by incubation in casein for 10 min at room temperature. AIB1 antibody was applied at 4°C overnight at a concentration of 5 µg/mL. EnVision (DAKO A/S, Glostrup, Denmark) was used for signal amplification, and positive staining was visualized using 3,3'-diaminobenzidine (Vector Laboratories, Burlingame, CA). Nuclei were counterstained with hematoxylin before mounting. Protein expression was evaluated by two observers using a semiquantitative weighted histoscore method (28–31). The interclass correlation coefficient for nuclear AIB1 obtained when comparing scores from two observers was 0.93. The specificity of the AIB1 antibody was checked by Western blotting using a standard protocol.

Immunohistochemistry using antibodies against epidermal growth factor receptor, HER2, and HER3 was done as described previously (24) and the cutoff was previously defined (24).

Fluorescence in situ hybridizations. AIB1 fluorescence in situ hybridization was done on the tissue microarrays using a probe mix consisting of Texas red–labeled DNA cosmid clones covering the AIB1 gene and FITC-labeled peptide nucleic acid probes for chromosome 20 (DAKO A/S). The mix was tested for specificity on metaphase spreads of normal cells and showed hybridization to 20q12. Fluorescence in situ hybridization was done using buffers from DAKO Histology FISH Accessory kit (DAKO A/S). In brief, dewaxed and rehydrated tissue was incubated in pretreatment solution for 10 min at 96°C, treated with pepsin for 18 min at 25°C, washed, dehydrated, and air dried. Ten microliters of probe mix were applied and denatured at 82°C for 22 min, and tissue was incubated overnight at 45°C in a humidified hybridization chamber. Tissue was washed in stringent wash buffer (DAKO A/S) for 10 min at 65°C, dehydrated, and air dried, and the slides were mounted in 0.5 µg/mL 4',6-diamidino-2-phenylindole in Vectashield antifade (Vector Laboratories). Gene copy number status was determined as the ratio of red signals (AIB1) over the number of green signals (chromosome) in 20 cancer cell nuclei for each tissue microarray core.

Statistical analysis. All statistical analysis was done using the SPSS statistical package (version 9.0 for Windows). Kaplan-Meier life tables with log-rank testing were plotted to assess overall survival (OS), disease-free survival (DFS), and DFS during treatment with tamoxifen. Spearman rank tests were conducted to test the associations between AIB1 and molecular or clinical markers. Cox's multivariate analysis (Cox's regression) was done with inclusion of biological markers alongside known predictive factors, such as size, nodal status, and grade. A value of P < 0.05 was considered statistically significant.


   Results
Top
 Abstract
 Materials and Methods
 Results
Discussion
 References
 
Patient information. All patients were treated with tamoxifen for a median of 5 years (range, 0.6-18 years) and followed up for a median of 6.45 years (range, 0.64-18.42 years). In addition to tamoxifen, 99 of 399 (24.8%) patients had chemotherapy (3 unknown) and 110 of 399 (27.57%) had radiotherapy (3 unknown). At the end of the study, there were 74 breast cancer–specific deaths and 100 breast cancer relapses, 78 of which occurred during tamoxifen treatment. Clinical and pathologic data are shown in Table 1 . Data on HER1-3 expression has been published previously (24).


View this table:
[in this window]
[in a new window]

  		Table 1. Patient clinical and pathologic variables

 
AIB1 protein expression. AIB1 expression was evaluated in 377 of 402 (93.8%) breast carcinomas. The remaining 25 cases were excluded from the study because of insufficient material, either due to loss of core or insufficient tumor material in the cores. AIB1 protein expression was confined to invasive breast carcinoma cells with no staining in normal breast epithelial cells. Due to weak cytoplasmic staining, only nuclear staining was analyzed (Fig. 1A and B ). High levels of AIB1 expression was weakly associated with high tumor levels of ER-{alpha} (correlation coefficient, 0.142; P = 0.006) and HER2 (correlation coefficient, 0.186; P = 0.001), whereas no association was noted between AIB1 expression and other molecular or clinical markers, such as tumor size, progesterone receptor expression, and time to relapse (data not shown). The median AIB1 histoscore was 58 (interquartile range, 30-100; Fig. 1C). For subsequent analysis, AIB1 expression was categorized as high (above upper quartile, histoscore of 100 and above) or low (below upper quartile; Fig. 1C) as described previously (6).


Figure 1
View larger version (43K):
[in this window]
[in a new window]

  		Fig. 1. A, photomicrographs of immunohistochemical staining in breast carcinoma showing nuclear AIB1 protein expression. B, breast carcinoma showing no staining in the absence of AIB1 antibody (negative control). Original magnification, x400. C, histogram showing the number of patients and the percentage of AIB1 positive breast cancer cells.

 
AIB1 protein expression and patient response to tamoxifen. Although there was a trend for patients whose tumors had high AIB1 expression to exhibit reduced OS compared with those whose tumor had low AIB1 expression (P = 0.059, log-rank test; data not shown), statistical significance was not reached. No significant association between tumor AIB1 expression and DFS or DFS on tamoxifen was observed (data not shown).

AIB1 and HER2 expression as a combined biological marker of patient outcome. Patients with HER2-positive tumors that expressed high levels of AIB1 (HER2/AIB1, n = 20, 5.5%) exhibited decreased DFS on tamoxifen (P = 0.042, log-rank test; Fig. 2 ) with a 2.20-fold increased risk of relapse [95% confidence interval (95% CI), 1.07-3.52; P = 0.0472; Table 2 ]. This group of patients also showed decreased OS (P = 0.036, log-rank test; data not shown) with a 2.26-fold (95% CI, 1.03-4.95; P = 0.041; Table 2) increased risk of dying from disease relative to patients whose tumors did not overexpress both HER2 and AIB1. No significant association was observed between patients with HER2/AIB1–overexpressing tumors and overall DFS (data not shown). Multivariate analysis did not suggest that tumor HER2/AIB1 overexpression was an independent marker of patient outcome either for DFS, DFS on tamoxifen, or OS when analyzed alongside known prognostic markers, such as tumor size, grade, and nodal status.


Figure 2
View larger version (11K):
[in this window]
[in a new window]

  		Fig. 2. Kaplan-Meier survival curve showing percentage DFS on tamoxifen of patients with HER2/AIB1–overexpressing tumors compared with all other patients. Cutoff values for high and low AIB1 levels are defined as above or below upper quartile. Cutoff values for high HER2 are defined as a HercepTest score of 2 or 3. Time to relapse on tamoxifen is the time from diagnosis to relapse during treatment with tamoxifen (years). Hazard ratio, which is relatively increased hazard from Cox's regression analysis for HER2/AIB1 patients relative to all the others, was 2.20 (95% CI, 1.07-3.52). P values represent log-rank testing of differences in survival.

 

View this table:
[in this window]
[in a new window]

  		Table 2. Hazard ratio

 
AIB1 and HER3 expression as a combined biological marker of patient outcome. Patients with HER3-positive tumors that expressed high levels of AIB1 (HER3/AIB1, n = 19, 5.6%) exhibited decreased DFS on tamoxifen (P < 0.001, log-rank test; Fig. 3 ) with a 3.67-fold increased risk of relapse (95% CI, 1.81-7.41; P < 0.001; Table 2). This group of patients also showed decreased OS (P < 0.001, log-rank test; data not shown) with a 3.79-fold (95% CI, 1.79-8.03; P < 0.001; Table 2) increased risk of dying from disease and increased risk of recurrence in general (P < 0.001, log-rank test) with a 3.35 risk (95% CI, 1.72-6.49; P < 0.001; Table 2) of recurrence relative to patients whose tumors did not overexpress both HER3 and AIB1. Multivariate analysis did, however, not suggest that tumor HER3/AIB1 overexpression was an independent marker of patient outcome either for DFS, DFS on tamoxifen, or OS when analyzed alongside known prognostic markers, such as tumor size, grade, and nodal status.


Figure 3
View larger version (11K):
[in this window]
[in a new window]

  		Fig. 3. Kaplan-Meier survival curve showing percentage DFS on tamoxifen of patients with HER3/AIB1–overexpressing tumors compared with all other patients. Cutoff values for high and low AIB1 levels are defined as above or below upper quartile. Cutoff values for high HER3 have been defined previously (24). Time to relapse on tamoxifen is the time from diagnosis to relapse during treatment with tamoxifen (years). Hazard ratio, which is the relatively increased hazard from Cox's regression analysis for HER2/AIB1 patients relative to all the others, was 2.047 (95% CI, 1.12-3.75). P values represent log-rank testing of differences in survival.

 
AIB1 and HER1-3 expression as combined biological marker of patient outcome. Overexpression of AIB1 in HER1-3–positive tumors (HER1-3/AIB1, n = 34, 10%) was significantly associated with a decreased DFS during the patient's treatment with tamoxifen (P = 0.003, log-rank test, Fig. 4A ) with a 2.42-fold increased risk of relapse (95% CI, 1.32-4.43; P = 0.004; Table 2). When patients were stratified according to their AIB1 expression and HER1-3 positivity (HER1-3/high AIB1, HER1-3/low AIB1, no HER1-3/high AIB1, and no HER1-3/low AIB1), patients with AIB1-overexpressing HER1-3–positive tumors had a significantly decreased DFS during the treatment with tamoxifen (P = 0.011, log-rank test, Fig. 4B) compared with the other three patient groups. These patients (HER1-3/AIB1) also showed significantly reduced overall DFS (P = 0.0371, log-rank test, Fig. 4C) and OS (P = 0.005, log-rank test, Fig. 4D) with a 1.79-fold (95% CI, 1.03-3.13; P = 0.039; Table 2) increased risk of relapse and a 2.40-fold (95% CI, 1.27-4.50; P = 0.007; Table 2) increased risk of dying of the disease. Multivariate analysis suggested that overexpression of AIB1 in HER1-3–positive tumors was an independent predictor of decreased DFS on tamoxifen (P = 0.023, Cox's regression) and OS (P = 0.044, Cox's regression) when analyzed alongside known prognostic markers, such as tumor size (P = 0.009 and 0.010 for DFS on tamoxifen and OS, respectively), grade (P = 0.013 and 0.001 for DFS on tamoxifen and OS, respectively), and nodal status (P = 0.0001 and 0.0001 for DFS on tamoxifen and OS, respectively).


Figure 4
View larger version (16K):
[in this window]
[in a new window]

  		Fig. 4. Kaplan-Meier survival curve showing percentage DFS on tamoxifen of patients with high AIB1/HER1-3–positive tumors compared with all other patients (A) or of patients with high AIB1/HER1-3–positive tumors compared with patients with high AIB1/no HER1-3 tumor expression (- - -), low AIB1/high HER1-3 tumor expression (......), and low AIB1/no HER1-3 (—) tumor expression (B). Kaplan-Meier survival curve showing percentage overall DFS of patients with high AIB1/HER1-3–positive tumors compared with all other patients (C). Kaplan-Meier survival curve showing percentage OS of patients with high AIB1/HER1-3–positive tumors compared with all other patients (D). Cutoff values for high and low AIB1 levels are defined as above or below upper quartile. Cutoff values for high HER1, HER2, and HER3 have been defined previously (24). Time to years relapse on tamoxifen is the time from diagnosis to relapse during treatment with tamoxifen (Y). Time to relapse is the time from diagnosis to relapse (Y). Hazard ratio, which is the relatively increased hazard from Cox's regression analysis for patients with high AIB1/HER1-3 positivity relative to the rest of the patients, was 2.42 (95% CI, 1.32-4.43), 1.79 (95% CI, 1.03-3.13), and 2.40 (95% CI, range 1.27-4.50), respectively, for relapse on tamoxifen, overall relapse, and OS. The discrepancies between the numbers of patients within the three curves are due to lack of information on relapse or death of one patient. P values represent log-rank testing of differences in survival.

 
AIB1 gene amplification. AIB1 gene amplification status was evaluated in 362 of 402 (90%) breast carcinomas. The remaining 40 cases were excluded from the study because of insufficient tumor material and loss of cores or because it was not possible to successfully fluorescence in situ hybridized the samples. AIB1 gene amplification was seen in 18 (5%) carcinomas (gene/chromosome ratio, 2.09-6.84). There was no consistent association between AIB1 gene amplification and AIB1 protein overexpression among the patients (data not shown).


   Discussion
Top
 Abstract
 Materials and Methods
 Results
 Discussion
References
 
Data presented here show the significant role of AIB1 in promoting early relapse and death following tamoxifen treatment in hormone-responsive HER-expressing clinical breast cancers. The study provides clinical evidence that suggests a cross-talk between ER-{alpha} and growth factor receptor pathways through changes in expression of specific coactivator proteins, such as AIB1 (6, 13).

In line with the study by Osborne et al (6), AIB1 expression alone was not a predictor of early relapse and death in this patient cohort. However, we confirmed that high AIB1 expression was a marker of tamoxifen resistance in HER2-overexpressing tumors (6) and also showed that high AIB1 expression was a highly significant marker of relapse and death of tamoxifen-treated patients with HER3-overexpressing tumors (Figs. 2 and 3). Patients with HER2/AIB1–overexpressing tumors exhibited 45% 10-year DFS on tamoxifen compared with 75% 10-year DFS on tamoxifen for all other patients (Fig. 2), whereas patients with HER3/AIB1–overexpressing tumors exhibited only 30% 10-year DFS on tamoxifen compared with 70% 10-year DFS on tamoxifen for all other patients (Fig. 3). The same patient groups also exhibited significantly 10-year reduced OS compared with the rest of the patients. AIB1 overexpression in HER2- or HER3-overexpressing tumors was, however, not an independent predictive marker of outcome in this patient cohort either for DFS during treatment with tamoxifen or OS when analyzed alongside known prognostic markers, such as tumor size, grade, and nodal status.

ER-{alpha}–positive tumors are more likely to be HER1 and HER2 negative as shown in this cohort of 402 ER-{alpha}–positive breast cancer patients, of which only tumors from six (1.5%) patients were HER1 positive and 51 (12.8%) tumors were HER2 positive. Subsequently, only tumors from 20 of 364 (5.5%) patients overexpressed both AIB1 and HER2. We have shown previously that patients from this cohort whose tumors were positive for one or more of HER1, HER2, or HER3 (HER1-3 positive) were significantly more likely to relapse on tamoxifen (24), and we therefore extended the study by Osborne et al. (6) and showed that HER1-3–positive tumors overexpressing AIB1 exhibited a significantly decreased DFS on tamoxifen (45%) compared with 75% for the rest of the patients (Fig. 4A and B; Table 1). In contrast to when AIB1 overexpression was analyzed in HER2- and HER3-overexpressing tumors, AIB1 overexpression in HER1-3–positive tumors was an independent marker of both decreased DFS on tamoxifen (P = 0.023, Cox's regression) and decreased OS (P = 0.044, Cox's regression) when analyzed alongside known prognostic markers. The putative value of AIB1 overexpression in HER1-3–positive tamoxifen-treated tumors could be of particular interest for the Tamoxifen Exemestane Adjuvant Multicenter (TEAM) Trial and Intergroup Exemestane Study (IES; ref. 2), in which patients are randomized to continued treatment with either an AI or tamoxifen following completion of 2 to 3 years of tamoxifen. To further investigate the potential role of AIB1 overexpression in HER1-3–positive tumors as an independent marker of early relapse and death in tamoxifen-treated breast cancers or as a marker for a switch to AI therapy after 2 to 3 years tamoxifen treatment, further work in a larger cohort of endocrine-treated breast cancers [TEAM; Arimidex Tamoxifen, Alone, or in Combination (ATAC); or IES] is required. This would also determine whether HER1-3–positive tumors with AIB1 overexpression are more responsive to endocrine therapies that work by mechanisms different from that of tamoxifen. ER-{alpha} coactivator levels and HER-mediated activation of ER-{alpha} are expected to be less important for therapies, such as AI treatment, which is designed to reduce the levels of estrogens rather than preventing the binding of estrogens to ER-{alpha}.

AIB1 activity is regulated by posttranslational modifications, including phosphorylation (10, 26). Six phosphorylation sites have been identified, and phosphorylation at all sites are necessary for activation (26, 27). A wide range of kinases, including p42/44 mitogen-activated protein kinase, p38 mitogen-activated protein kinase, and I{kappa}B kinases, mediate AIB1 phosphorylation and subsequently its binding to ER-{alpha} (10, 26). Currently, we are aiming to use immunohistochemistry to validate activated AIB1 as a marker of early relapse and death of tamoxifen-treated breast cancer patients on tumors from this patient cohort as well as tumors from the TEAM study.

We observed only 5% (18 cases) of patients form this cohort with AIB1 gene amplification (15, 16, 18, 19). The lower amplification rate could be due to the fact that ER-{alpha}–positive breast carcinomas are normally less aggressive tumors. The small number of AIB1 amplified cases prevented robust analysis of AIB1 gene amplification as a marker of tamoxifen resistance; however, to further investigate the predictive and/or prognostic role of amplification of AIB1, a larger cohort of both endocrine-treated and untreated breast cancer patients needs to be investigated.

Tamoxifen has been the standard first-line adjuvant endocrine treatment of postmenopausal metastatic breast cancers since the 1970s; however, alternative endocrine therapy, such as treatment with AIs, is often effective after disease relapse because most patients remain ER-{alpha} positive. The present study confirms that AIB1 is amplified or overexpressed in a subgroup of primary breast carcinomas. Our data also extend previous data by showing that AIB1 expression in HER1-3–positive tumors might be an independent marker for early relapse and death on tamoxifen-treated breast cancers. The predictive or prognostic value of these combined markers should be further investigated along with other established putative markers in similar data sets, such as TEAM or ATAC, to verify their value in selection of tamoxifen or AI-based endocrine treatment.


   Footnotes
 
Grant support: European Union grant MTK1-CT2004-509858 (T. Kirkegaard).

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: Current address for J.M.S. Bartlett: Endocrine Cancer Group, Edinburgh Cancer Research Centre, Western General Hospital, Edinburgh EH4 2XR, United Kingdom.

Received 8/ 3/06; revised 11/22/06; accepted 12/ 8/06.


   References
Top
 Abstract
 Materials and Methods
 Results
 Discussion
 References
 

  1. Gradishar WJ. Tamoxifen—what next? Oncologist 2004;9:378–84.[Abstract/Free Full Text]
  2. Coombes RC, Hall E, Gibson LJ, et al. A randomized trial of exemestane after two to three years of tamoxifen therapy in postmenopausal women with primary breast cancer. N Engl J Med 2004;350:1081–92.[Abstract/Free Full Text]
  3. Early Breast Cancer Trialists' Collaborative Group (EBCTCG). Effects of chemotherapy and hormonal therapy for early breast cancer on recurrence and 15-year survival: an overview of the randomised trials. Lancet 2005;365:1687–717.[CrossRef][Medline]
  4. Shou J, Massarweh S, Osborne CK, et al. Mechanisms of tamoxifen resistance: increased estrogen receptor-HER2/neu cross-talk in ER/HER2-positive breast cancer. J Natl Cancer Inst 2004;96:926–35.[Abstract/Free Full Text]
  5. Osborne CK, Schiff R. Growth factor receptor cross-talk with estrogen receptor as a mechanism for tamoxifen resistance in breast cancer. Breast 2003;12:362–7.[CrossRef][Medline]
  6. Osborne CK, Bardou V, Hopp TA, et al. Role of the estrogen receptor coactivator AIB1 (SRC-3) and HER-2/neu in tamoxifen resistance in breast cancer. J Natl Cancer Inst 2003;95:353–61.[Abstract/Free Full Text]
  7. Schiff R, Massarweh S, Shou J, Osborne CK. Breast cancer endocrine resistance: how growth factor signaling and estrogen receptor coregulators modulate response. Clin Cancer Res 2003;9:447–54S.
  8. Martini PG, Katzenellenbogen BS. Modulation of estrogen receptor activity by selective coregulators. J Steroid Biochem Mol Biol 2003;85:117–22.[CrossRef][Medline]
  9. Tamrazi A, Carlson KE, Rodriguez AL, Katzenellenbogen JA. Coactivator proteins as determinants of estrogen receptor structure and function: spectroscopic evidence for a novel coactivator-stabilized receptor conformation. Mol Endocrinol 2005;19:1516–28.[Abstract/Free Full Text]
  10. Font DM, Brown M. AIB1 is a conduit for kinase-mediated growth factor signaling to the estrogen receptor. Mol Cell Biol 2000;20:5041–7.[Abstract/Free Full Text]
  11. Tsai MJ, O'Malley BW. Molecular mechanisms of action of steroid/thyroid receptor superfamily members. Annu Rev Biochem 1994;63:451–86.[CrossRef][Medline]
  12. Clarke R, Liu MC, Bouker KB, et al. Antiestrogen resistance in breast cancer and the role of estrogen receptor signaling. Oncogene 2003;22:7316–39.[CrossRef][Medline]
  13. Schiff R, Massarweh SA, Shou J, Bharwani L, Mohsin SK, Osborne CK. Cross-talk between estrogen receptor and growth factor pathways as a molecular target for overcoming endocrine resistance. Clin Cancer Res 2004;10:331–6S.
  14. Takimoto GS, Graham JD, Jackson TA, et al. Tamoxifen resistant breast cancer: coregulators determine the direction of transcription by antagonist-occupied steroid receptors. J Steroid Biochem Mol Biol 1999;69:45–50.[CrossRef][Medline]
  15. List HJ, Reiter R, Singh B, Wellstein A, Riegel AT. Expression of the nuclear coactivator AIB1 in normal and malignant breast tissue. Breast Cancer Res Treat 2001;68:21–8.[CrossRef][Medline]
  16. Anzick SL, Kononen J, Walker RL, et al. AIB1, a steroid receptor coactivator amplified in breast and ovarian cancer. Science 1997;277:965–8.[Abstract/Free Full Text]
  17. McKenna NJ, Lanz RB, O'Malley BW. Nuclear receptor coregulators: cellular and molecular biology. Endocr Rev 1999;20:321–44.[Abstract/Free Full Text]
  18. Bautista S, Valles H, Walker RL, et al. In breast cancer, amplification of the steroid receptor coactivator gene AIB1 is correlated with estrogen and progesterone receptor positivity. Clin Cancer Res 1998;4:2925–9.[Abstract]
  19. Murphy LC, Simon SL, Parkes A, et al. Altered expression of estrogen receptor coregulators during human breast tumorigenesis. Cancer Res 2000;60:6266–71.[Abstract/Free Full Text]
  20. Gullick WJ. c-erbB-4/HER4: friend or foe? J Pathol 2003;200:279–81.[CrossRef][Medline]
  21. Tidcombe H, Jackson-Fisher A, Mathers K, Stern DF, Gassmann M, Golding JP. Neural and mammary gland defects in ErbB4 knockout mice genetically rescued from embryonic lethality. Proc Natl Acad Sci U S A 2003;100:8281–6.[Abstract/Free Full Text]
  22. Stern DF. ErbBs in mammary development. Exp Cell Res 2003;284:89–98.[CrossRef][Medline]
  23. Long W, Wagner KU, Lloyd KC, et al. Impaired differentiation and lactational failure of Erbb4-deficient mammary glands identify ERBB4 as an obligate mediator of STAT5. Development 2003;130:5257–68.[Abstract/Free Full Text]
  24. Tovey S, Dunne B, Witton CJ, Forsyth A, Cooke TG, Bartlett JM. Can molecular markers predict when to implement treatment with aromatase inhibitors in invasive breast cancer? Clin Cancer Res 2005;11:4835–42.[Abstract/Free Full Text]
  25. Yarden Y, Sliwkowski MX. Untangling the ErbB signalling network. Nat Rev Mol Cell Biol 2001;2:127–37.[CrossRef][Medline]
  26. Zheng FF, Wu RC, Smith CL, O'Malley BW. Rapid estrogen-induced phosphorylation of the SRC-3 coactivator occurs in an extranuclear complex containing estrogen receptor. Mol Cell Biol 2005;25:8273–84.[Abstract/Free Full Text]
  27. Wu RC, Qin J, Yi P, et al. Selective phosphorylations of the SRC-3/AIB1 coactivator integrate genomic reponses to multiple cellular signaling pathways. Mol Cell 2004;15:937–49.[CrossRef][Medline]
  28. Kirkegaard T, Witton CJ, McGlynn LM, et al. AKT activation predicts outcome in breast cancer patients treated with tamoxifen. J Pathol 2005;207:139–46.[CrossRef][Medline]
  29. Edwards J, Krishna NS, Grigor KM, Bartlett JM. Androgen receptor gene amplification and protein expression in hormone refractory prostate cancer. Br J Cancer 2003;89:552–6.[CrossRef][Medline]
  30. Fraser JA, Reeves JR, Stanton PD, et al. A role for BRCA1 in sporadic breast cancer. Br J Cancer 2003;88:1263–70.[CrossRef][Medline]
  31. Kirkegaard T, Edwards J, Tovey S, et al. Observer variation in immunohistochemical analysis of protein expression, time for a change? Histopathology 2006;48:787–94.[CrossRef][Medline]



This article has been cited by other articles:


Home page
 Cancer Res.Home page
M. P. Fereshteh, M. T. Tilli, S. E. Kim, J. Xu, B. W. O'Malley, A. Wellstein, P. A. Furth, and A. T. Riegel
The Nuclear Receptor Coactivator Amplified in Breast Cancer-1 Is Required for Neu (ErbB2/HER2) Activation, Signaling, and Mammary Tumorigenesis in Mice
Cancer Res., May 15, 2008; 68(10): 3697 - 3706.
[Abstract] [Full Text] [PDF]

Home page
 Endocr. Rev.Home page
G. Arpino, L. Wiechmann, C. K. Osborne, and R. Schiff
Crosstalk between the Estrogen Receptor and the HER Tyrosine Kinase Receptor Family: Molecular Mechanism and Clinical Implications for Endocrine Therapy Resistance
Endocr. Rev., April 1, 2008; 29(2): 217 - 233.
[Abstract] [Full Text] [PDF]

Home page
 Cancer Res.Home page
T. Lahusen, M. Fereshteh, A. Oh, A. Wellstein, and A. T. Riegel
Epidermal Growth Factor Receptor Tyrosine Phosphorylation and Signaling Controlled by a Nuclear Receptor Coactivator, Amplified in Breast Cancer 1
Cancer Res., August 1, 2007; 67(15): 7256 - 7265.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kirkegaard, T.
Right arrow Articles by Bartlett, J. M.S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kirkegaard, T.
Right arrow Articles by Bartlett, J. M.S.

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