Citations

Abstract Background: Neoadjuvant endocrine therapy (NET) trials serve to inform design and selection of agents for larger adjuvant endocrine trials. The neoadjuvant aromatase inhibitor (AI) trial ACOSOG Z1031 randomized the treatment of postmenopausal women with ER rich (Allred 6-8) clinical stage 2/3 breast cancer to either EXE, ANA and LET. The results are therefore of interest in the context of new data that compares these AIs in the adjuvant setting. The opportunity to develop predictive biomarker tests for NET sensitivity was also a key study objective in order guide future selection of patients for inclusion in studies that compare NET versus neoadjuvant chemotherapy (NCT). The value of a baseline PAM50 intrinsic subtype test for NET patient selection was therefore an embedded objective of the study. Methods: Of the 374 women who began study treatment on Z1031, pretreatment biopsy specimen for central IHC testing for ER and Ki67 was available on 304 patients. The PAM50 intrinsic subtype test (PMCID: 2667820) could be conducted on 170 baseline samples. The Preoperative Endocrine Prognostic Index (PEPI) an approach to predicting long term outcomes based on pathological stage and surgical specimen ER and Ki67 status was also conducted because patients with a PEPI of zero (T1/2 N0, ER+, Ki67<=2.7%) have been found to have an excellent long term prognosis and therefore unlikely to benefit from chemotherapy (PMCID: 255670). Results: The degree of Ki67 suppression, the absolute level of Ki67 in the surgical specimen and the PEPI results were not significantly different by treatment arm (Kruskal-Wallis tests p >0.05). Thirty Percent (95%CI: 19.6-42.9%) of women with pre-AI LumA subtype and 12% (95%CI: 6.4-20.0%) of women with pre-AI LumB subtype had a PEPI of zero predicting excellent prognosis. Multivariate logistic modeling found that the likelihood of a PEPI score of zero is 3.2 fold higher (95%CI: 1.43 7.12) among 66 women with a pre-AI LumA subtype compared to 100 women with a pre-AI LumB subtype. Additional baseline variables (clinical T and N stage, HER2 status, pre-AI Ki-67 level (< = 10% vs. >10%) were not found to modify the chance of a PEPI of zero. Baseline PAM50 Subtype versus PEPI Conclusion: The results of Z1031 show no differences in clinical or biologic response between LET, EXE, and ANA in the neoadjuvant setting; predicting that no difference in efficacy will be seen between these agents in adjuvant studies. Pre-AI LumA versus LumB status, defined by the PAM50 subtype, identifies patients who are more likely to be in the most favorable PEPI score following neoadjuvant AI therapy. Patients with pretreatment LumA status may, therefore, not be suitable for a randomized trial of NET versus NCT since approximately one third of these patients may be able to avoid chemotherapy altogether. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S1-2.

Abstract Background: The non-steroidal reversible aromatase inhibitor (AI), anastrozole (A) is approved as adjuvant monotherapy in hormone receptor (HR) positive early breast cancer (EBC). The steroidal irreversible AI exemestane (E) is approved in sequence after an initial 2-3 years of tamoxifen. MA27 tested the hypothesis that exemestane would have greater efficacy and better end-organ safety than anastrozole for several reasons: E is an irreversible and more potent AI than A; unlike A, E does not induce intra-tumoral aromatase and; through its mild androgenic activity E may exert a second anti-tumor effect and a more favorable bone and lipid metabolism profile than A. Initially the study also tested the role of a cyclooxygenase-2 inhibitor, celecoxib, used in combination with an AI. However, celecoxib was discontinued early in MA27 following identification of cardiovascular toxicity with COX-2 inhibitors. Methods: Postmenopausal women with hormone receptor positive primary breast cancer were randomized after adequate local treatment to 5 years of adjuvant A (1mg/day) or E (25mg/day) with or without celecoxib/placebo (400mg/plac twice daily for 3 years). The primary objective is the comparison of event free survival (EFS) between women treated with A or E. Secondary objectives include overall survival (OS), distant recurrence (DDFS), incidence of contralateral breast cancer (CBC) and safety. Quality of Life in a subset of women has been evaluated, and a very extensive tissue bank created. Stratification included: prior chemotherapy; lymph node status, celecoxib (during use), aspirin use (during randomization to celecoxib), and trastuzumab use (since November 2005). The primary endpoint (EFS) will look for an improvement from 87.5% to 89.9%; HR 0.80, 2-sided 5% level and 80% power, with 644 events required. Results: 7576 women were randomized between June 2003 and July 2008. Celecoxib/placebo, was discontinued 2 years into the trial in December 2004 after 1635 patients had received celecoxib. The number of events required for final analysis was reached April 2010. Patient characteristics were balanced for age (median 64.1yrs); race; ECOG PS; mastectomy; TNM staging and; prior adjuvant chemotherapy. EFS, OS, DDFS, and CBC as well as clinical fractures, cardiovascular events and adverse events will be presented by arm in the final analysis. Conclusions: NCIC CTG MA.27 is the first definitive EBC trial comparing a non-steroidal and steroidal AI as initial adjuvant therapy. Exemestane is not currently approved as initial adjuvant treatment and superiority or equivalence will lead to its inclusion as a first-line option for EBC in postmenopausal HR positive breast cancer. Efficacy, clinical fractures, cardiovascular events and AI related symptoms will help to define the cost-benefit ratios of these two AIs. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S1-1.

Abstract Identification of HER2 as an important cellular marker in the biology and treatment of breast cancer has highlighted the importance of reliable testing methodology. Controversy exists regarding type of test, reliability, definition of positivity, and which test may best predict for patient (pt) efficacy to anti-HER2 therapies. Purpose: To determine the concordance between HER2 results by 3 central laboratories, impact of round-robin adjudication of discordant cases, and heterogeneity in HER2 results using specimens from 3 adjuvant trials where HER2 testing was performed by local and central laboratories for enrollment. Methods: We performed a blinded round-robin exchange of randomly sampled, HER2-normal (IHC-& FISH-) and HER2-positive breast tumors among 3 central laboratories (NCCTG, BCIRG and NSABP) for confirmatory HER2 testing. The 3 laboratories performed immunohistochemistry (IHC) for HER2 using the HercepTest kit (Dako, Carpenteria, CA) and fluorescence in situ hybridization (FISH) for HER2 using the PathVysion HER2 DNA probe kit/HER2/CEN17 probe mixture (Abbott Molecular, Des Plaines, IL) on 389 tumor specimens obtained from N9831/BCIRG006 (37 IHC+/FISH+, 33 IHC+/FISH-, 36 IHC-/FISH+, 62 IHC-& FISH-) and BCIRG005 (96 IHC-& FISH-); 123 cases had ≥2 blocks examined from the same pt. HER2 positivity was defined according to FDA-approved guidelines used in the clinical trials (IHC+: 3+ complete membrane staining in >10% cells; FISH+: HER2/CEN17 ratio ≥2.0). The HER2 status (IHC: 3+ vs 0-2+; FISH: amplified vs not) for each block was independently determined at each site; discordant IHC and FISH cases were adjudicated at a face-to-face meeting. Results: Independent reads were concordant across pathologists in IHC status in 351/381 (92%) cases and in FISH status in 343/373 (92%) cases. Upon adjudication, a consensus was reached on 16 and 18 of the discordant IHC and FISH cases, respectively. Among 96 BCIRG005 cases, IHC-and FISH-were confirmed in the primary block in all 96 cases. Among 59 evaluable N9831 HER2-normal cases, IHC-and FISH-were confirmed in the primary block in 57 (97%) cases (but another block tested HER2+ for 4 cases). Among 102 N9831/BCIRG006 HER2+ cases, HER2 positivity was confirmed in the primary block in 73 (72%) cases. Among 118 cases with IHC results for > 1 block, the adjudicated IHC result agreed across blocks in 106 (90%) cases. Among 113 cases with FISH results for >1 block, the adjudicated FISH result agreed in 107 (95%) cases. Among 53 N9831 HER2-normal cases adjudicated as IHC-& FISH-(although they all had a previous local HER2+ test), there was significant improvement in disease-free survival associated with trastuzumab given concurrently with paclitaxel after doxorubicin and cyclophosphamide compared to chemotherapy alone (HR=0.31, 95% CI 0.11-0.91; A 23 pts, 10 events; C 30 pts, 5 events). Conclusions: Excellent agreement (96%) was observed among the pathologists at adjudication, suggesting that standardized methods improve assay proficiency. HER2 heterogeneity across blocks was observed more at the protein than at the gene level. In the small subset of N9831 pts adjudicated as HER2-normal trastuzumab benefit was observed. This work was supported by NCI and Genentech. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD10-02.

Abstract Purpose: Emerging data from cooperative group trials suggests that not all patients with a positive SLN require completion axillary lymph node dissection (ALND). The controversy regarding who will benefit from additional nodal clearance continues, suggesting a need for improved tools to predict non-SLN involvement. We hypothesized that the size of a SLN metastasis evaluated as a continuous variable would be an important predictor of non-SLN involvement. The goal of this study was to determine clinicopathologic factors including SLN metastasis size that predicted non-SLN involvement and to use these factors to construct an improved predictive nomogram. Methods: Using a prospective database, we identified 509 patients with invasive breast cancer from 1996 - 2007 with a positive SLN who underwent ALND. Patients receiving neoadjuvant therapy were excluded. Clinicopathologic data including age, primary tumor size, presence of multifocal disease, histology (invasive ductal vs. invasive lobular vs. mixed invasive), tumor grade, estrogen receptor, progesterone receptor, and HER2/neu status, presence of lymphovascular invasion (LVI), the number of SLNs identified, number of positive SLNs, the maximum SLN metastasis size and the presence of extranodal extension were recorded. For SLNs described only as containing isolated tumor cells, size was recorded as 0.1 mm. Univariate and multivariate logistic regression analyses were performed to identify factors predictive of positive non-SLNs. Using these variables, a nomogram was constructed and subsequently validated using an external cohort of 464 patients. Results: On univariate analysis, the following factors were predictive of positive non-SLNs: number of SLN identified (p<.001), number of positive SLN (p<.001), maximum SLN metastasis size (p<.001), extranodal extension (p<.001), primary tumor size (p=.001), LVI (p=.019) and histology (p=.034). On multivariate analysis, all factors remained significant at the 5% level except LVI. A nomogram was created using these variables. When applied to an external cohort, the nomogram was accurate and discriminating with an area under the receiver operating characteristic curve of .73 (95% CI: .68 - .77). Conclusions: SLN metastasis size is predictive for identifying additional disease in the axilla. These data have been incorporated into a nomogram that accurately predicts the likelihood of having additional, non-SLN metastasis suggesting that routine reporting of the SLN metastasis size would assist with clinical decision making regarding the need to perform a completion ALND. Figures available in online version. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD06-08.

Abstract Background: A major issue surrounding the use of therapeutic drugs for the treatment of breast cancer is the eventual development of resistance. Endoxifen, the most potent tamoxifen metabolite, is being developed as a novel endocrine therapy for the treatment of endocrine responsive breast cancer patients. While numerous studies have investigated the process of tamoxifen resistance, no such data exist regarding the mechanism by which cells develop resistance to endoxifen. Here, we describe the development and characterization of a novel endoxifen resistant MCF7 breast cancer cell line and the identification of a specific treatment to effectively target these resistant cells. Methods: MCF7 cells were chronically exposed to concentrations of endoxifen previously demonstrated to be associated with the greatest reductions in estrogen stimulated proliferation and transcription (1000 nM). Changes in the physiological and molecular properties of these cells were monitored during the course of resistance using a wide range of techniques. Results: Following 15 months of endoxifen exposure, an epithelial to mesenchymal transition (EMT) was induced in MCF7 cells, characterized by loss of E-cadherin expression, up-regulation of fibronectin and vimentin expression and increased responsiveness to TGFβ. Resistant cells exhibit a 7-fold increase in their proliferation rates relative to parental cells and display basal like properties (triple negative) due to silencing of ERα , progesterone receptor and CD24 expression. Resistant cells were confirmed to be estrogen insensitive through the use of cell proliferation and gene expression studies. Wound healing and cell migration assays revealed that resistant cells are highly aggressive with a significant level of metastatic potential. Microarray analysis revealed over 7500 genes to be differentially expressed in the resistant cell line relative to parental cells using a 2-fold cutoff, of which only 52 genes (0.7%) were determined to be up-regulated. Interestingly, a number of the most highly altered genes have previously been implicated in the development of EMT and/or resistance including Twist2, IGF binding protein 5, GATA and β-tubulin. Based on the identification of P-tubulin as the most up-regulated gene in resistant cells, 2-methoxyestradiol (2ME2) was recognized as a candidate drug to specifically target this resistant cell line due to it known roles in blocking tubulin polymerization. Indeed, 2ME2 exposure resulted in the induction of apoptosis and significant cell death in vitro. Conclusions: Chronic exposure of MCF7 cells to high concentrations of endoxifen led to induction of EMT with cells that are basal like, estrogen and SERM insensitive, highly TGFP responsive with significantly increased proliferation rates and metastatic potential relative to parental cells. These findings suggest that the mechanisms of resistance to endoxifen may differ from those observed with long term exposure to tamoxifen and have identified 2ME2 as a potentially successful alternative therapy for endoxifen resistant breast cancer cells. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD05-11.

Abstract Background: NSABP P1 and P2 are the largest prevention trials of tamoxifen and raloxifene in women at high risk of developing breast cancer. Both agents have been shown to decrease, but not eliminate breast cancer risk in these women. The goal of our study was to identify single nucleotide polymorphisms (SNPs) associated with development of breast cancer in high-risk women treated with tamoxifen or raloxifene. Methods: We performed a nested matched case-control genome-wide association study (GWAS) in subjects entered on the P2, which included only postmenopausal women, and subjects at least 50 years old entered on the P1 phase III prevention trials who were treated with tamoxifen or raloxifene. Cases were defined as subjects who developed invasive breast cancer or ductal carcinoma in situ and each was matched to two controls based on trial (P1, P2), age at trial entry, Gail risk score, history of lobular carcinoma in situ, and time on study. The study was restricted to the 94% of subjects self-identified as Caucasian. Genotyping was performed with the Illumina Human610-Quad chip. Eigenstrat analyses were performed to control for population stratification. SNPs were imputed within 200 Kb on either side of regions containing SNPs with p ≤ 3E-05. CYP2D6 genotyping was performed on all subjects. Results: The GWAS included 592 cases and 1171 controls. 547,356 SNPs were used in the analyses after removing 14,019 for call rates less than 98%, 30,560 for minor allele frequencies <1%, and 301 with Hardy-Weinberg equilibrium p-value <1E-06. Eigenvectors did not alter the results when used as covariates. Eleven genotyped SNPs with p-values ranging from 2.12E-06 to 9.98E-06 (conditional logistic regression with eigenvector adjustment) were identified; and 22 SNPs with p < 4E-05 were identified by imputation around these SNPs on chromosomes (Chr) 4, 8, 9, 13, 16 and 22, which were then genotyped with the Invader platform. Following imputation and genotyping, initial functional genomic studies have focused on 8 SNPs on Chr 16 (p-values 1.81E-06 to 9.55E-06, with the lowest p-value for an imputed and fine mapped SNP), all of which were in ZNF423, a gene known to encode a protein that associates with SMAD family members. In lymphoblastoid cell lines genotyped for the 2 top SNPs in ZNF423 (rs8060157 and rs11076499) and stably transfected with estrogen receptor-α, the variant and wild type SNPs displayed striking differences in estradiol-induced expression of ZNF423, SMAD3, BRCA1, and BRCA2. Conclusions: This GWAS revealed SNPs associated with the development of breast cancer in high-risk women treated with tamoxifen or raloxifene. Genome-wide significance was not achieved, but SNPs in ZNF423 identified on Chr 16 were associated with differential expression of ZNF423, SMAD3, BRCA1, and BRCA2 in response to estradiol in vitro, providing direction for future research. (Supported in part by NIH grants U01GM61388, U01GM63173, P50CA116201, U10CA77202, U10CA37377, U10CA69974, U24CA114732, and the Biobank Japan Project funded by the Ministry of Education, Culture, Sports, Science and Technology, Japan) Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD05-02.

Abstract The central importance of the HER2/Neu/EGFR/RAS signaling pathway has been well established in the growth, invasion and metastasis of human breast cancer, even though oncogenic RAS mutations are rare in breast cancer, activation of the tumor-promoting ERBB/RAS/MEK/MAPK pathway has been consistently documented in high-grade breast tumors. As such, novel approaches to inhibit activated ERBB/RAS signals constitute important measures to block tumor growth and metastasis in mammary tumors. In this study, instead of targeting an upstream signaling component such as HER2/EGFR/RAS, we targeted the most downstream signaling module identified in the RAS pathway — the SIAH proteolytic machinery. SIAH is an evolutionarily conserved RING E3 ligase that is a critical “gatekeeper” required for RAS signal transduction in human cancer cells. SIAH is specifically expressed in tumor cells in 120 human breast cancer patients examined so far. The increased SIAH expression is correlated with increased grades and aggressiveness of human breast cancer. We then asked whether inhibiting the gatekeeper function of SIAH would be effective in blocking mammary tumorigenesis and metastasis in human breast cancer. Our results indicated that SIAH2-deficiency successfully abolished tumor growth of three breast cancer cell lines (MDA-MB-231, MDA-MB-435 and MDA-MB-468) in soft agar assays as well as in athymic nude mice. Importantly, by inhibiting SIAH2 function in highly aggressive human breast cancer cells, we are able to completely block tumorigenesis and metastasis of two highly invasive and metastatic human breast cancer cell lines (MDA-MB-231 and MDA-MB-435). These findings suggest that SIAH2 may be an attractive new therapeutic target for novel breast cancer therapy and developing anti-SIAH molecules will aid in expanding our arsenal of effective anticancer therapies. More effective breast cancer treatments may be obtained by multi-pronged synergistic inhibitions at upstream (HER2/EGFR membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in the HER2/EGFR/RAS pathway in parallel. Thus, by attacking the growth-promoting ERBB/RAS pathway at multiple signaling modules simultaneously, we may be in a great position to halt the genesis, progression and metastasis of human breast cancer. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-14.

Abstract Background: NKTR-102, a topoisomerase 1 inhibitor-polymer conjugate with reduced peak concentrations and a continuous concentration profile, demonstrated evidence of anti-tumor activity in a broad range of tumors in phase 1 (Von Hoff; EORTC-NCI-AACR 2008, abstract #595), including three patients (pts) with triple negative breast cancer (one confirmed PR by RECIST, one 20% reduction in tumor burden and one 50%+ reduction in CA 27.29). We now report data of a randomized phase 2 study in pts with MBC following progression to taxane-based therapy. Methods: This open-label, phase 2 study enrolled pts to receive NKTR-102 intravenously (IV) at a target dose of 145 mg/m2. Eligible patients had progressive MBC following taxane therapy, ECOG PS 0-1, adequate renal, hepatic, and marrow function. The study randomized pts to receive NKTR-102 q14d or q21d; each schedule followed a two-stage Simon design to ensure adequate response rate prior to proceeding to full enrollment. The primary endpoint was objective response rate (ORR) by RECIST v1.0; secondary endpoints were safety and PFS. Results: 70 pts were randomized from Feb09 to Apr10 and treated (35 on each schedule); 20 patients remain active on study as of 14Jun2010. Median age was 55 (range 33-83); all but 1 pt was female. ECOG PS 0/1 equaled 40%/60%. Prior neo-adjuvant and adjuvant therapy had been administered in 15 and 39 patients respectively; 23 pts had received prior hormonal therapy. Median number of prior non-hormonal regimens for metastatic disease was 2 (range 0-4). All pts had received prior taxane therapy; 11 in the adjuvant setting and 60 in the metastatic setting). 45 pts had received only prior anthracycline/taxane therapy (“AT”); an additional 14 pts had received prior AT/capecitabine therapy (“ATC”). 42 were estrogen or progesterone receptor positive and 20 pts had triple negative disease. Best RECIST response rate (confirmed and unconfirmed) equaled 27% (9 pts; 2 awaiting confirmation) and 24% (8 pts; 4 awaiting confirmation) for the q14d and q21d schedules (n=33 and 34, respectively; 3 patients had not undergone first on-study CT exam). As ORR results were similar for each schedule, the combined best RECIST ORR for in AT/ATC pts equaled 23%/29%, respectively and in pts with triple negative disease, this equaled 25%. Common related Grade 3/4 toxicities (q14d/q21d schedules; n=67 pts with AE data available): diarrhea (15%/12%), neutropenia (15%/9%),fatigue (12%/3%), and dehydration (6%/3%). One pt in each schedule died due to septic shock and acute renal failure secondary to hypovolemia. Conclusion: Single-agent NKTR-102 demonstrates significant anti-tumor activity in pts with MBC, including pts having tumor progression after ATC-based therapy and pts with triple negative disease, with a tolerable toxicity profile. Mature ORR and median PFS will be available by December 2010. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-11-01.

Abstract The association between hormone replacement therapy (HRT) and breast cancer risk in women with benign breast disease (BBD) is unclear. However, others have shown that HRT use is associated with the development of proliferative breast disease (Rohan et. al, CEBP 2008). To better clarify potential risks associated with postmenopausal hormone use in women with BBD, we performed a nested case control study within the Mayo Clinic Benign Breast Disease Cohort. In the cohort, there are 11,079 women who had benign breast biopsies between 1967 and 1996 and for whom we have outcome and risk factor data, including use of HRT. We studied 947 cases (breast cancer after BBD) and two controls matched to each case based on age and year of BBD. Information on use of HRT was obtained through use of questionnaires and medical record review with a mean time of follow up of 17.4 years. HRT use, histology, involution status, and family history were all evaluated for impact on breast cancer risk in a multivariate model. As shown in Table 1, when looking at effects of histology, involution, and family history, we confirmed previously reported findings of risk (Hartmann LC et. al, NEJM 2005). Specifically, we saw increased risk in women with AH vs. PDWA or NP, decreased risk with complete involution vs. partial or no involution, and increased risk with strong family history vs. weak or no family history. Associations of hormone replacement therapy and other relevant clinical variables with risk of breast cancer Multivariate model simultaneously including all variables listed in the table. HRT=hormone replacement therapy. NP=non-proliferative. PDWA=proliferative disease without atypia. AH=atypical hyperplasia We found that women who had used HRT had no higher risk of developing breast cancer than women who had not used HRT. Specifically, with Never Users as the reference group, those with 5 years or less exposure had OR 0.80 (0.56-1.15); 6-10 years, 0.85 (0.56-1.28) and 11+ years, 0.51 (0.36-0.72), p =0.002. In conclusion, we found that HRT use among postmenopausal women with BBD was not associated with an increased risk of breast cancer. In this case-control set, we confirmed previous findings regarding well established risk factors of histology, involution status, and family history. While HRT use may contribute to the development of proliferative breast disease, we do not see that HRT is associated with additional breast cancer risk, beyond that of the proliferative disease itself. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-09-03.

Abstract Background: Approximately 5-10% of all breast cancers are hereditary and the majority of these arise due to germline mutations in the BRCA1 and BRCA2 tumour suppressor genes. BRCA1 is involved in multiple cellular pathways including DNA damage signalling, DNA repair, cell cycle regulation, protein ubiquitination, chromatin remodelling, transcriptional regulation and apoptosis. Several distinct pathological features can be used to estimate the likelihood of the presence of a BRCA1 mutation, however, it is not yet possible to fully categorise a BRCA1 mutated tumour. BRCA1-associated breast cancers are generally defined as being ER (Estrogen Receptor) negative and indeed triple negative for ER, PR and HER2. However, approximately 10-36% of BRCA1 mutated breast cancers are, in fact, ER positive. These tumours less frequently demonstrate the characteristics more commonly associated with BRCA 1 -associated breast cancers. Initial molecular evidence also suggests that there is heterogeneity within BRCA1-associated breast tumours and this is dependent on the presence or absence of the estrogen receptor. The aims of this study are to investigate the underlying biology of BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast tumours. Methods: Extensive gene expression profiling and data analysis was performed on a cohort of 70 FFPE (Formalin Fixed Paraffin Embedded) derived BRCA1 mutated breast tumours and matched sporadic controls using the ALMAC Breast Cancer DSA™ research tool. Within this dataset we have generated molecular profiles of: (1) BRCA 1 -mutated ER positive and (2) BRCA1-mutated ER negative breast cancer. Functional analysis was performed using DAVID and METACORE. Validation of gene targets was performed by qRT-PCR and Western blotting. Results: A list of differentially expressed transcripts was derived from the comparison of 35 BRCA1 mutant breast tumours and 35 matched sporadic controls. Further analysis based on the presence and absence of ER identified a set of transcripts defining BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast cancer. Functional analysis of these two datasets has identified the main pathways and processes that are deregulated. Specifically, BRCA1-deficiency in the absence of ER was associated with deregulation of pathways implicated in immune response whereas BRCA 1 deficiency in the presence of ER was associated with pathways implicated in cell adhesion and cytoskeletal remodelling. Validation of the key genes underlying these two BRCA1-deficient breast cancer subtypes has been performed. Discussion: This approach has revealed significant heterogeneity within BRCA1 mutated breast cancer based on the presence or absence of ER. Significant differences in the transcripts and molecular processes underlying BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast tumours have been identified. The ability to identify BRCA 1 -deficiency by gene expression profiling from FFPE derived breast tissue may also have significant clinical application. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-04-14.