Search

We conducted a phase IIa, multi-centre, open label, single arm study (RADICAL; NCT01791985) of AZD4547 (a potent and selective inhibitor of Fibroblast Growth Factor Receptor (FGFR)-1, 2 and 3 receptor tyrosine kinases) administered with anastrozole or letrozole in estrogen receptor positive metastatic breast cancer patients who had become resistant to aromatase inhibitors. After a safety run-in study to assess safety and tolerability, we recruited 52 patients. The primary endpoint was change in tumour size at 12 weeks, and secondary endpoints were to assess response at 6 weeks, 20 weeks and every 8 weeks thereafter and tolerability of the combined treatment. Two partial responses (PR) and 19 stable disease (SD) patients were observed at the 12-week time point. At 28 weeks, according to centrally reviewed Response Evaluation Criteria in Solid Tumours (RECIST) criteria, five PR and 8 SD patients were observed in 50 assessable cases. Overall, objective response rate (5 PR) was of 10%, meeting the pre-specified endpoint. Fourteen patients discontinued due to adverse events. Eleven patients had retinal pigment epithelial detachments which was asymptomatic and reversible in all but one patient. Exploratory ribonucleic acid sequencing (RNA-Seq) analysis was done on patients' samples: 6 differentially-expressed-genes could distinguish those who benefited from the addition of AZD4547. FGFR-1 upregulation has been associated with endocrine therapy resistance in breast cancer patients. Here the authors report the results of a phase IIa study to assess the safety and efficacy of AZD454, an inhibitor of FGFR-1, 2 and 3 receptor tyrosine kinases, in combination with anastrozole or letrozole, in estrogen receptor positive breast cancer patients. [ABSTRACT FROM AUTHOR]

Background: Effective anticancer therapy is thought to involve induction of tumour cell death through apoptosis and/or necrosis. [18F]ICMT-11, an isatin sulfonamide caspase-3/7-specific radiotracer, has been developed for PET imaging and shown to have favourable dosimetry, safety, and biodistribution. We report the translation of [18F]ICMT-11 PET to measure chemotherapy-induced caspase-3/7 activation in breast and lung cancer patients receiving first-line therapy.Results: Breast tumour SUVmax of [18F]ICMT-11 was low at baseline and unchanged following therapy. Measurement of M30/M60 cytokeratin-18 cleavage products showed that therapy was predominantly not apoptosis in nature. While increases in caspase-3 staining on breast histology were seen, post-treatment caspase-3 positivity values were only approximately 1%; this low level of caspase-3 could have limited sensitive detection by [18F]ICMT-11-PET. Fourteen out of 15 breast cancer patients responded to first-line chemotherapy (complete or partial response); one patient had stable disease. Four patients showed increases in regions of high tumour [18F]ICMT-11 intensity on voxel-wise analysis of tumour data (classed as PADS); response was not exclusive to patients with this phenotype. In patients with lung cancer, multi-parametric [18F]ICMT-11 PET and MRI (diffusion-weighted- and dynamic contrast enhanced-MRI) showed that PET changes were concordant with cell death in the absence of significant perfusion changes.Conclusion: This study highlights the potential use of [18F]ICMT-11 PET as a promising candidate for non-invasive imaging of caspase3/7 activation, and the difficulties encountered in assessing early-treatment responses. We summarize that tumour response could occur in the absence of predominant chemotherapy-induced caspase-3/7 activation measured non-invasively across entire tumour lesions in patients with breast and lung cancer. [ABSTRACT FROM AUTHOR]

Correction to: I Nature Communications i https://doi.org/10.1038/s41467-022-30666-0 In the original version of this article, the following author (Veronica Ferguson) was omitted from the author list. Author list, Author contributions and competing interests statements have now been updated in both the PDF and HTML versions of the article. [Extracted from the article]

Background:The Intergroup Exemestane Study (IES) (ISRCTN11883920) demonstrated improved survival for postmenopausal women with ER-positive/unknown primary breast cancer who switched to exemestane after 2-3 years tamoxifen, compared with those continuing on tamoxifen to complete 5 years therapy. This was achieved without detriment to on-treatment quality-of-life (QoL). We report on- and post-treatment QoL impact in IES.Methods:A total of 582 patients from 8 countries participated in the QoL substudy. Functional Assessment of Cancer Therapy-Breast (FACT-B) and endocrine symptom subscale (ES) were completed at baseline, 3, 6, 9, 12, 18, 24, 30, 36, 48 and 60 months. The primary endpoint was FACT-B Trial Outcome Index (TOI); secondary endpoints included severity of individual endocrine symptoms.Results:Both the groups showed gradual improvement in overall QoL and lessening of total endocrine symptoms post treatment compared with baseline (P<0.002). There was no evidence of any between-group differences in TOI. Vasomotor complaints remained high on treatment. Vaginal discharge was more frequent (P<0.01) with tamoxifen up to 24 months from baseline. In both the groups, post-treatment libido did not recover to baseline levels.Conclusion:Clinical benefits of switching to exemestane are accompanied by good overall QoL. Although some symptoms persist, the majority of endocrine symptoms improve after treatment completion. [ABSTRACT FROM AUTHOR]

Background: Human epidermal growth factor receptor 2 (HER2) is amplified and overexpressed in 20-25% of breast cancers. This study investigated circulating free DNA (cfDNA) for detection of HER2 gene amplification in patients with breast cancer.Methods: Circulating free DNA was extracted from plasma of unselected patients with primary breast cancer (22 before surgery and 68 following treatment), 30 metastatic patients and 98 female controls using the QIAamp Blood DNA Mini Kit (Qiagen). The ratio of HER2 to an unamplified reference gene (contactin-associated protein 1 (CNTNAP1)) was measured in cfDNA samples by quantitative PCR (qPCR) using SK-BR-3 cell line DNA as a positive control.Results: We validated the qPCR assay with DNA extracted from 23 HER2 3+ and 40 HER2-negative tumour tissue samples; the results agreed for 60 of 63 (95.2%) tumours. Amplification was detected in cfDNA for 8 of 68 patients following primary breast cancer treatment and 5 of 30 metastatic patients, but was undetected in 22 patients with primary breast cancer and 98 healthy female controls. Of the patients with amplification in cfDNA, 10 had HER2 3+ tumour status by immunohistochemistry.Conclusions: The results demonstrate for the first time the existence of amplified HER2 in cfDNA in the follow-up of breast cancer patients who are otherwise disease free. This approach could potentially provide a marker in patients with HER2-positive breast cancer. [ABSTRACT FROM AUTHOR]

Gamma-secretase activity is vital for the transmembrane cleavage of Notch receptors and the subsequent migration of their intracellular domains to the nucleus. Notch overexpression has been associated with breast, colon, cervical and prostate cancers. We tested the effect of three different gamma-secretase inhibitors (GSIs) in breast cancer cells. One inhibitor (GSI1) was lethal to breast cancer cell lines at concentrations of 2 muM and above but had a minimal effect on the non-malignant breast lines. GSI1 was also cytotoxic for a wide variety of cancer cell lines in the NCI60 cell screen. GSI1 treatment resulted in a marked decrease in gamma-secretase activity and downregulation of the Notch signalling pathway with no effects on expression of the gamma-secretase components or ligands. Flow cytometric and western blot analyses indicated that GSI1 induces a G2/M arrest leading to apoptosis, through downregulation of Bcl-2, Bax and Bcl-XL. GSI1 also inhibited proteasome activity. Thus, the gamma-secretase inhibitor GSI1 has a complex mode of action to inhibit breast cancer cell survival and may represent a novel therapy in breast cancer. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether primary breast cancer patients showed evidence of circulating tumour cells (CTCs) during follow-up as an alternative to monitoring disseminated bone marrow tumour cells (DTCs) by immunocytochemistry and reverse transcriptase (RT)–PCR for the detection of micrometastases. We planned to compare CTC and DTC frequency in low-risk and high-risk patients. We identified two cohorts of primary breast cancer patients who were at low (group II, T1N0, n=18) or high (group III, >3 nodes positive (with one exception, a patient with two positive nodes) n=33) risk of relapse who were being followed up after primary treatment. We tested each cohort for CTCs using the CellSearch system on 1–7 occasions and for DTCs by immunocytochemistry and RT–PCR on 1–2 occasions over a period of 2 years. We also examined patients with confirmed metastatic disease (group IV, n=12) and 21 control healthy volunteers for CTCs (group I). All group I samples were negative for CTCs. In contrast, 7 out of 18 (39%) group II primary patients and 23 out of 33 (70%) group III patients were positive for CTCs (P=0.042). If we count only samples with >1 cell as positive: 2 out of 18 (11%) group II patients were positive compared with 10 out of 33 (30%) in group III (P=0.174). In the case of DTCs, 1 out of 13 (8%) group II patients were positive compared with 19 out of 27 (70%) in group III (P<0.001). Only 10 out of 33 (30%) patients in group III showed no evidence of CTCs in all tests over the period of testing, compared with 11 out of 18 (61%) in group II (P=0.033). A significant proportion of poor prognosis primary breast cancer patients (group III) have evidence of CTCs on follow-up. Many also have evidence of DTCs, which are more often found in patients who were lymph node positive. As repeat sampling of peripheral blood is more acceptable to patients, the measurement of CTCs warrants further investigation because it enables blood samples to be taken more frequently, thus possibly enabling clinicians to have prior warning of impending overt metastatic disease.British Journal of Cancer (2009) 100, 160–166. doi:10.1038/sj.bjc.6604773 www.bjcancer.com Published online 25 November 2008 [ABSTRACT FROM AUTHOR]

Estrogen receptora(ERa) is a ligand-inducible transcription factor that acts to regulate gene expression by binding to palindromic DNA sequence, known as the estrogen response element, in promoters of estrogen-regulated genes. In breast cancer ERaplays a central role, where estrogen-regulated gene expression leads to tumor initiation, growth and survival. As an approach to silencing estrogen-regulated genes, we have studied the activities of a fusion protein between ERaand the promyelocytic leukemia zinc-finger (PLZF) protein, a transcriptional repressor that acts through chromatin remodeling. To do this, we have developed lines from the estrogen-responsive MCF-7 breast cancer cell line in which the expression of the fusion protein PLZF-ERais conditionally regulated by tetracycline and shows that these feature long-term silencing of the expression of several well-characterized estrogen-regulated genes, namely pS2, cathepsin-D and the progesterone receptor. However, the estrogen-regulated growth of these cells is not inhibited unless PLZF-ERaexpression is induced, an observation that we have confirmed both in vitro and in vivo. Taken together, these results show that PLZF-ERais a potent repressor of estrogen-regulated gene expression and could be useful in distinguishing estrogen-regulated genes required for the growth of breast cancer cells.Gene Therapy (2005) 12, 452-460. doi:10.1038/sj.gt.3302421 Published online 13 January 2005 [ABSTRACT FROM AUTHOR]

Currently, the therapy for breast cancer is determined by immunohistochemical staining of the primary tumour for oestrogen receptor alpha (ERa). However, a proportion of ERa-positive patients fail to respond to tamoxifen and a proportion of ERa-negative patients show response. Here, we describe a novel procedure for the purification of malignant breast epithelial cells in an attempt to identify these patients at an early stage. Using this procedure, we are able to purify malignant cells to >90% purity as determined by immunohistochemical staining, cytology and fluorescent in situ hybridisation (FISH). While the malignant cells can be maintained in culture they do not proliferate in contrast to purified breast epithelial cells from reduction mammoplasties. Moreover, ERa and progesterone receptor (PR) expression is maintained in malignant cells, whereas normal epithelial cells rapidly lose Era and PR. Functional studies were performed on the separated malignant cells in terms of their response to oestradiol and tamoxifen. Four out of the seven ERa-positive tumours showed a significant reduction in cell numbers after tamoxifen treatment compared to oestradiol, ERa negative tumours failed to show a response. We conclude that (a) it is possible to purify and maintain breast cancer cells for a sufficient period to permit functional studies and (b) ERa is retained in culture facilitating the use of these cells in studies of the mechanism of endocrine response and resistance in vitro.British Journal of Cancer (2003) 88, 1071-1076. doi:10.1038/sj.bjc.6600866 www.bjcancer.com [ABSTRACT FROM AUTHOR]

Fibroblast growth factor 8 can transform NIH3T3 cells and its expression has been found to be associated with breast and prostate cancer. Following our finding that fibroblast growth factor 8 mRNA expression is increased in breast cancer, we have undertaken an immunohistochemistry study of fibroblast growth factor 8 expression in a series of human breast tissues and other normal tissues. Our findings confirm increased expression of fibroblast growth factor 8 in malignant breast tissue but also show significant fibroblast growth factor 8 expression in non-malignant breast epithelial cells. No significant difference in fibroblast growth factor 8 expression was found between different grades of ductal carcinoma, lobular carcinoma and ductal carcinoma in-situ or cancer of different oestrogen receptor, progesterone receptor or nodal status. The highest levels of fibroblast growth factor 8 expression were found in lactating breast tissues and fibroblast growth factor 8 was also detected in human milk. A survey of other normal tissues showed that fibroblast growth factor 8 is expressed in the proliferative cells of the dermis and epithelial cells in colon, ovary fallopian tube and uterus. Fibroblast growth factor 8 appears to be expressed in several organs in man and appears to have an importance in lactation. [ABSTRACT FROM AUTHOR]

Fibroblast growth factor 8 (FGF8) is an important developmental protein which is oncogenic and able to co-operate with wnt-1 to produce mouse mammary carcinoma. The level of expression of FGF8 mRNA was measured in 68 breast cancers and 24 non-malignant breast tissues. Elevated levels of FGF8 mRNA were found in malignant compared to non-malignant breast tissues with significantly more malignant tissues expressing FGF8 (P=0.019) at significantly higher levels (P=0.031). In situ hybridization of breast cancer tissues and analysis of purified populations of normal epithelial cells and breast cancer cell lines showed that malignant epithelial cells expressed FGF8 mRNA at high levels compared to non-malignant epithelial and myoepithelial cells and fibroblasts. Although two of the receptors which FGF8 binds to (FGFR2-IIIc, FGFR3-IIIc) are not expressed in breast cancer cells, an autocrine activation loop is possible since expression of fibroblast growth factor receptor (FGFR) 4 and FGFR1 are retained in malignant epithelial cells. This is the first member of the FGF family to have increased expression in breast cancer and a potential autocrine role in its progression. [ABSTRACT FROM AUTHOR]

One hundred and sixteen patients with locally advanced or metastatic breast cancer were randomized to receive CMF (cyclophosphamide 600 mg m(-2) day 1 and 8 i.v., 5-fluorouracil 600 mg m(-2) day 1 and 8 i.v., methotrexate 40 mg m(-2) day 1 and 8 i.v., monthly for 6 cycles) or MM (methotrexate 30 mg m(-2), mitoxantrone 6.5 mg m(-2), both i.v. day 1 3-weekly for 8 cycles) as first line treatment with chemotherapy. Objective responses occurred in 17 patients out of 58 (29%) who received CMF and nine out of 58 (15%) who received MM; 95% confidence interval for difference in response rates (-1%-29%), P = 0.07. No statistically significant differences were seen in overall survival or time to progression between the two regimes although a tendency towards a shorter progression time on the MM regime must be acknowledged. There was, however, significantly reduced haematological toxicity (P < 0.001) and alopecia (P < 0.001) and fewer dose reductions and delays in patients randomized to MM. No statistically significant differences were seen between the two regimes in terms of quality of life (QOL). However, some association between QOL and toxicity was apparent overall with pooled QOL estimates tending to indicate a worsening in psychological state with increasing maximum toxicity over treatment. Despite the fact that results surrounding response rates and time to progression did not reach statistical significance, their possible compatibility with an improved outcome on CMF treatment must be borne in mind. However, MM is a well-tolerated regimen with fewer side-effects than CMF, which with careful patient management and follow-up, therefore, may merit consideration as a first-line treatment to palliate patients with metastatic breast cancer who are infirm or elderly. [ABSTRACT FROM AUTHOR]

Of 312 patients presenting with breast cancer to a single clinic, 297 were screened for metastases in skin and nodes, bone, marrow, liver and lungs, using standard clinical, radiological scanning and cytological techniques. Thirty-four patients were found to have overt metastatic disease using these tests. Metastases were demonstrable on chest X-ray in 6.1% of the entire group of patients, on the bone scan in 4.2%, liver scan in 1.5%, liver ultrasound in 1.2% and in the bone marrow in only a single patient; 3.8% had contralateral or supraclavicular lymph node metastases or skin metastases. Twenty-eight of these 34 patients (82%) with overt metastases would have been classed as metastatic had only chest X-ray and clinical examination been carried out. A survey was then carried out to determine when tests for bone and liver metastases became abnormal. Bone scan and skeletal survey results were reviewed in 58 patients, 22 of whom had developed skeletal metastases and all of whom had regular skeletal scintigraphy carried out. Sixteen of 20 (80%) scans carried out within six months of the development of skeletal deposits were abnormal compared with 4 of 19 (21%) scans at the same follow-up time in those who failed to develop metastases, but few patients showed definite evidence of bone metastases on scanning prior to radiological metastases. Fifty-one patients who were found to have liver metastases at post-mortem were reviewed and most showed progressively rising alkaline phosphatase before death but only 11 of 57 (19.2%) and 14 of 50 (28%) had positive liver scintiscans and liver ultrasound examinations respectively from 3-12 months before death. [ABSTRACT FROM AUTHOR]

Presents the results of a study on the disease-free survival of postmenopausal women with primary breast cancer who switched to the aromatase inhibitor exemestane after tamoxifen therapy. Characteristics of the aromatase inhibitor; Number of first events that occurred in the study, including metastatic recurrence; Hazard ratio of reduced incidence of contralateral breast cancer in the exemestane group.

Background: Intergroup Exemestane Study (IES) was a randomised study that showed a survival benefit of switching adjuvant endocrine therapy after 2-3 years from tamoxifen to exemestane. PathIES aimed to assess the potential prognostic and predictive value of ERβ1 and ERβ2 expression in primary tumours in order to determine benefit in the two treatment arms. Patients and methods: Primary tumour samples were available for 1256 patients (27% IES population). ERβ1 and ERβ2 expression was dichotomised at the median IHC score (high if ERβ1 ≥ 191, ERβ2 ≥ 164). Hazard ratios (HRs) were estimated by multivariable Cox proportional hazards models adjusting for clinicopathological factors. Treatment effects with biomarker expressions were determined by interaction tests. Analysis explored effects of markers both as a continuous variable and with dichotomised cut-offs. Results: Neither ERβ1 nor ERβ2 were associated with disease-free survival (DFS) or overall survival (OS) in the whole cohort. In patients treated with continued tamoxifen, high ERβ1 expression compared with low was associated with better DFS [HR = 0.38:95% confidence interval (CI) 0.21-0.68, P = 0.001]. DFS benefit of exemestane over tamoxifen (HR = 0.40:95% CI 0.22-0.70) was found in the low ERβ1 subgroup (interaction P = 0.01). No significant difference with treatment was observed for ERβ2 expression in either DFS or OS. Conclusion: In the PathIES population, exemestane appeared to be superior to tamoxifen among patients with low ERβ1 expression but not in those with high ERβ1 expression. This is the first trial of its kind to report a parameter potentially predicting benefit of an aromatase inhibitor when compared with tamoxifen and an independent validation is warranted. [ABSTRACT FROM AUTHOR]

Purpose: Breast cancer is associated with adverse outcomes in patients with the metabolic syndrome phenotype. To study this further, we examined the relationship between serum metabolite levels and the components of metabolic syndrome with treatment outcomes in breast cancer. Methods: A total of 88 women with measurable breast cancer were studied; their serum metabolites as assessed by 1H nuclear magnetic resonance spectroscopy, blood pressure, lipids, glucose, body mass index and waist circumference were recorded and correlated with treatment response. Results: We identified metabolic syndrome in approximately half of our cohort (42 patients) and observed a significant trend (P = 0.03) of increased incidence of metabolic syndrome in partial response (33.3%), stable disease (42.9%) and progressive disease groups (66.1%). High blood sugar predicted a poor response (P < 0.001). Logistic regression of metabonomic data demonstrated that high lactate (P = 0.03) and low alanine (P = 0.01) combined with high glucose (P = 0.01) were associated with disease progression. Conclusions: Metabolic syndrome is commonly observed in metastatic breast cancer and these patients have poorer outcomes. These data, which support our previous findings, suggest that high blood glucose as part of metabolic syndrome is associated with a poor response in breast cancer. They also validate new therapeutic approaches that focus on metabolism. [ABSTRACT FROM PUBLISHER]

Background: The antiestrogen tamoxifen may have partial estrogen-like effects on the postmenopausal uterus. Aromatase inhibitors (AIs) are increasingly used after initial tamoxifen in the adjuvant treatment of postmenopausal early breast cancer due to their mechanism of action: a potential benefit being a reduction of uterine abnormalities caused by tamoxifen. [ABSTRACT FROM PUBLISHER]

Introduction: Steroid receptor coactivator 3 (SRC3) acts as a coactivator of nuclear receptors including estrogen receptor-alpha (ER). SRC3 has been implicated in the pathogenesis of breast cancer (BC) as well as in resistance to endocrine therapy. SRC3 is phosphorylated at a number of residues following the stimulation of growth factors or hormones. Tyr24 and Ser543 are both phosphorylated upon estrogen stimulation, while Tyr24 is modulated by JNK and Ser543 by both p38 and JNK. To date, the importance and potential role of phosphorylation at these residues has not been explored in BC. In this study we assessed the protein expression of SRC3, pTyr24 and pSer543 and association with clinico-pathological features and outcome in a well defined breast cancer series. Methods: The expressions of SRC3, pTyr24 and pSer543 were assessed in the Nottingham Tenovus Primary Breast Cancer Series which consists of 1650 cases of primary invasive. SRC3, pTyr24 and pSer543 were correlated with clinico-pathological data as well as outcome. Results: SRC3 expression was significantly associated with unfavourable clinicopathological features including ER -ve (p = 0.02), PR -ve (p = .038), HER2 overexpression (p < 0.0001), Triple negative phenotype (p = 0.001), high proliferation (p < 0.0001), high histological grade (p < 0.001), and lympho-vascular invasion. On contrast, the expression of pSer543 was significantly associated with a luminal phenotype, well differentiation, low proliferation (low mitotic index, low Ki67 and low SPAG5; p < 0.0001), hormonal receptors (ERα+ve/PR+ve/AR+ve), absence of both ER-B1 and ER-B5 (p < 0.01), high expression of ER -α associated proteins (cyclin D1 and Bcl2; p < 0.0001), high expression of c-jun (p < 0.0001), JNK (p < 0.0001), SRC3 (p < 0.0001), T24 (p < 0.001) and active p53 transcriptional pathways that regulate cell cycle progression and apoptosis (MDM2+ve, MDM4+ve and Bax+ve; p < 0.01) and absence of basal like phenotypes (p < 0.01). The absence of pSer543 was significantly associated with loss of expression of the key DNA repair proteins including XRCC1 (p < 0.0001), BRCA1 (p < 0.0001), ATM (p = 0.008) and TOP2A (p < 0.0001) reflecting a higher risk of genomic instability. Moreover, absence of pSer543 was more common in BC with a triple negative phenotype (p < 0.001). With regard to outcome, no association with outcome based on the expression of SRC3 either with or without tamoxifen was observed. However, expression of pSer543 was associated with significantly longer disease free survival (DFS) (p < 0.00001) and breast cancer specific survival (BCSS) (p = 0.0001). Furthermore, absence of pSer543 was associated with both a shorter DFS (p = 0.007) and BCSS (p = 0.01) in ER+ ve high risk BC. pSer534 was confirmed as an independent prognostic factor after adjustment for endocrine therapy and other validated prognostic factors and absent of pSer534 was associated with a two-fold increased risk of recurrence (HR = 1.9, CI 95%= 1.2-3.1). Data on Tyr24 will also be presented. Conclusion: Phosphorylation at Ser543 is associated with a luminal phenotype, positive prognostic factors and sensitivity to tamoxifen. Furthermore, it is an independent prognostic factor. pS543 is a novel prognostic marker in BC and warrants further investigation. [ABSTRACT FROM AUTHOR]

Background: Our recent human kinome screening to identify new regulators of estrogen receptor a (ERa) suggested an important role of kinase suppressor of ras 1 (KSR1) in breast cancer. KSR1 was originally identified as a positive regulator interacting with both RAS and RAF in the mitogen-activated protein kinase (MAPK) pathway. Recent studies have suggested that KSR1 may have dual functions as a scaffolding protein and also a protein kinase. Although KSR1 has been implicated in Ras-dependent cancers, its clinical significance and function in breast cancer have not been elucidated. Methods: The clinical significance of KSR1 was assessed by analyzing its expression in 2 breast cancer tissue microarrays (TMAs, n=1000) by immunohistochemistry. Pearson chi and Fisher's Exact Test were used to correlate the expression levels with various tumor biomarkers; Kaplan Meier analyses were used to investigate impact on disease-free (DFS) and overall survival (OS). Multivariate Cox-proportional hazards analysis was also performed to evaluate the significant of KSR1 as an independent factor in breast cancer-specific survival (BCSS) and disease-free interval (DFI). The expression levels of KSR1 in breast cancer cell lines were measured by RT-qPCR and western blotting. A KSR1 stable over-expression breast cancer cell line (MCF7-KSR1) was generated to study its effect on growth and colony formation by 3D matrigel assay and soft agar assay in vitro. Furthermore, MCF7-KSR1 stable cells were also used in nude mice xenograft model in vivo. Luciferase reporter assay was employed to examine the effect of KSR1 on p53 transcriptional activity. Further immunofluorescence staining, western blotting and reporter assays were performed to elucidate the interaction between KSR1, BRCA1 and p53. Results: KSR1 was expressed with low (60%) and high levels (40%) in breast cancer patients. High expression correlated significantly with longer DFS (p = 0.014) and longer OS (p = 0.012) in more than 20 yrs follow-up. Interestingly, KSR1 was positively associated with BRCA1 (p = 0.002) and reversely with p53 (p = 0.038). High KSR1 levels were a significant predictor of longer breast cancer-specific survival BCSS (p = 0.001) and longer disease free interval DFI (p = 0.002) independent of tumour stage, grade and size. RT-qPCR and western blotting demonstrated that KSR1 is ubiquitously expressed in breast cancer cell lines. In vitro 3D matrigel and soft agar assay showed that MCF7-KSR1 cells had a significant decreased number of colonies and formed smaller size colonies compared to MCF7-vector cells. Furthermore, over-expression of KSR1 (MCF7-KSR1) significantly suppressed the growth of breast cancer xenografts in nude mice. Finally, KSR1 was involved in the functional interaction between BRCA1 and p53 and elevated KSR1 potentially resulted in up-regulated BRCA1. KSR1 also inhibited p53-dependent transcriptional activity through suppression of p53 acetylation and promotion of p53 neddylation. Conclusion: KSR1 is an independent prognostic factor in breast cancer and high KSR1 expression correlates with longer DFS and OS. Furthermore, it is potential that KSR1 is important in tumour suppression by its involvement in functional feedback regulation of BRCA1 and p53. [ABSTRACT FROM AUTHOR]