Background Multiple myeloma is a plasma cell tumour with approximately 5500 new cases in the UK each year. Ixazomib is a next generation inhibitor of the 20S proteasome and is thought to be an effective treatment for those who have relapsed from bortezomib. The combination of cyclophosphamide and dexamethasone (CD) is a recognised treatment option for patients with relapsed refractory multiple myeloma (RRMM) who have relapsed after treatment with bortezomib and lenalidomide, whilst also often being combined with newer proteasome inhibitors. The most apparent combination for ixazomib is therefore with CD. Methods MUK eight is a randomised, controlled, open, parallel group, multi-centre phase II trial that will recruit patients with RRMM who have relapsed after treatment with thalidomide, lenalidomide, and a proteasome inhibitor. The primary objective of the trial is to evaluate whether ixazomib in combination with cyclophosphamide and dexamethasone (ICD) has improved clinical activity compared to CD in terms of progression-free survival (PFS). Secondary objectives include comparing toxicity profiles and the activity and cost-effectiveness of both treatments. Since opening, the trial has been amended to allow all participants who experience disease progression (as per the IMWG criteria) on the CD arm to subsequently switch to receive ICD treatment, once progression has been confirmed with two clinical members of the Trial Management Group (TMG). This ‘switch’ phase of the study is exploratory and will assess second progression-free survival measured from randomisation to second disease progression (PFS2) and progression-free survival from the point of switching to second disease progression (PFS Switch) in participants who switch from CD to ICD treatment. Discussion Development of ixazomib offers the opportunity to further investigate the value of proteasome inhibition through oral administration in the treatment of RRMM. Previous studies investigating the safety and efficacy of ICD in patients with RRMM demonstrate a toxicity profile consistent with ixazomib in combination with lenalidomide and dexamethasone, whilst the combination showed possible activity in RRMM patients. Further investigation of the anti-tumour effect of this drug in RRMM patients is therefore warranted, especially since no trials comparing CD with ICD have been completed at present. Trial registration ISRCTN number: ISRCTN58227268 . Registered on 26 August 2015.

Abstract Background and aims Treatment of relapsed/refractory myeloma (RRMM) remains a challenge as most approved and commonly accessible doublet treatments induce responses (≥PR) in less than half of patients. The combination of the classical alkylator cyclophosphamide with thalidomide (CTD) or lenalidomide (CRD) is standard of care in early lines of therapy in the UK and elsewhere. Data on the clinical value of cyclophosphamide and pomalidomide combination therapy in RRMM is currently sparse and lacking for patients that have previously been treated with cyclophosphamide in earlier lines of therapy. Material and Methods MUKseven is a randomised phase II study for RRMM patients comparing cyclophosphamide (500 mg po d1, 8, 15), pomalidomide (4 mg days 1-21) and dexamethasone (40 mg; if ≥75 years 20 mg; d1, 8, 15, 21) (CPd) versus standard pomalidomide and dex (Pd). Patients with ≥2 prior lines of therapy were randomised 1:1 to receive either CPd or Pd and treated until progression. The primary endpoint of the study is PFS, secondary endpoints include response, OS and safety and toxicity. Patients underwent bone marrow sampling and peripheral blood collection at baseline, on treatment and at relapse to correlate outcomes with disease biology. The original sample size was 250 patients but due to approval of pomalidomide by the UK funding agency NICE mid-recruitment, and resulting low enrolment rates, a decision was made to close the trial early. Results In total 102 evaluable RRMM patients were randomised between March 2016 and February 2018, 51 each to CPd and Pd treatment arms that were comparable regarding age, gender, ISS and ECOG performance status. Patients had received a median of 3 prior lines of therapy (range 2-8); all had been treated with proteasome inhibitors and lenalidomide and 94% of patients had received cyclophosphamide as part of earlier lines of therapy. Trial entry criteria were permissive and allowed ongoing red cell, platelet and growth factor support to reflect real-world practice in RRMM - 11% of patients required platelet and 16% G-CSF support before starting trial therapy. Treatment with CPd was associated with a significantly higher response rate (≥PR) of 68.6% (95% CI: 54.1 - 80.9%) compared to 47.1% (CI: 32.9 - 61.5%) for Pd (P=0.018). Five patients (9.8%) on CPd treatment reached CR vs. none with Pd therapy (Table 1). PFS data is currently maturing and will be presented at the conference. At the time of abstract submission 20 patients were still on trial treatment and 22.5% of evaluable patients had received trial therapy for 12 months or longer. Anaemia, fatigue and infection of any grade were common side effects and similar in frequency between treatment arms, whereas higher grade cytopenias were more frequent with CPd than Pd. More patients experienced at least one SAE with CPd treatment (44 patients) than with Pd (36 patients). Over 80% of SAEs suspected to be related to study drug for CPd and Pd arms were infections or cytopenias requiring admission for iv therapy. Five patients on the CPd arm and 4 patients on Pd discontinued therapy due to toxicity. Site and patient adherence to central bone marrow and peripheral blood collection was high with 92% of baseline samples, 87% at C1D14, 87% at C4D14 and 43% of samples at relapse received by central laboratories. High risk genetic lesions gain(1q), del(17p) and adverse translocations t(4;14), t(14;16) and t(14;20) were profiled, amongst other changes, using molecular assays (digital MLPA, TaqMan). Of the 66 patients for whom complete results were available at the point of abstract submission, 48.5% were found to have 1 high risk lesion and 13.6% ≥2 high risk lesions ("double-hit"). The best response achieved in patients with double hit tumours was PR in 1 out of 9 evaluable patients. Further genetic profiling and related exploratory analyses are ongoing. Discussion The combination of cyclophosphamide, pomalidomide and dexamethasone significantly increases response rates and depth of response compared to pomalidomide and dexamethasone in RRMM patients, even those that have already been exposed to cyclophosphamide combination therapy in previous lines of therapy. Primary endpoint PFS data for CPd vs. Pd will be presented at the conference. Analyses of outcomes in the context of molecular profiles are ongoing and will be presented at the conference. Disclosures Pawlyn: Celgene Corporation: Consultancy, Honoraria, Other: Travel support; Takeda Oncology: Consultancy, Other: Travel support; Amgen: Consultancy, Honoraria, Other: Travel Support; Janssen: Honoraria, Other: Travel support. Garg:Amgen: Honoraria, Other: Travel Support; Novartis: Other: travel support, Research Funding; Janssen: Honoraria; Takeda: Other: Travel Grant. Boyd:Novartis: Consultancy, Honoraria; Janssen: Honoraria, Other: Travel and Accommodation expenses; Celgene: Consultancy, Honoraria, Other: Advisory role. Cook:Bristol-Myers Squibb: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Glycomimetics: Consultancy, Honoraria; Celgene Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Seattle Genetics: Honoraria; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Speakers Bureau. Kaiser:Amgen: Consultancy, Honoraria; Takeda: Consultancy, Other: travel support; Bristol-Myers Squibb: Consultancy, Other: travel support; Janssen: Consultancy, Honoraria; Chugai: Consultancy; Celgene: Consultancy, Honoraria, Research Funding.

Abstract Background and aims Existing evidence regarding the effect of low-dose cyclophosphamide on immune cells in myeloma patients, in particular in combination with the IMiD® compound pomalidomide is limited. We present here for the first time changes in immune cell sub-group composition associated with the addition of cyclophosphamide to pomalidomide in the randomised MUKseven clinical trial. Material and Methods MUKseven is a randomised phase II study for relapsed or refractory myeloma (RRMM) patients comparing cyclophosphamide (500 mg po d1, 15, 21), pomalidomide and dexamethasone (CPd) versus standard pomalidomide and dex (Pd). Patients with ≥2 prior lines of therapy were randomised 1:1 to CPd or Pd and treated until disease progression. All patients underwent bone marrow sampling and peripheral blood collection, the latter for immune cell immunophenotyping at Cycle 1 Day 1 (C1D1; Baseline), C1D14 (on-treatment), C4D14 (on-treatment) and at disease progression. Peripheral blood (PB) T-cell populations were profiled using multicolor flow cytometry (MFC) designed to assess baseline and pharmacodynamic changes in subpopulations including helper, cytotoxic, naïve, memory, and activated/proliferating phenotypes (CD3, CD4, CD8, CD45RA, CD62L, HLA-DR, Ki67. T-cell sub-populations were defined and their respective % of total lymphocyte population used for downstream analyses. Results In total 102 evaluable RRMM patients were randomised, 51 each to CPd and Pd treatment arms, with comparable clinical baseline characteristics. Patients had received a median of 3 prior lines of treatment. Evaluable PB immune profiling data was available for 93 (91%) patients at Baseline, 83 (81%) at C1D14, 55 (54%) at C4D14 and 26 (25%) at progression. We observed trends for changes in baseline T-cell population composition with increasing numbers of prior lines of therapy. Specifically, mean % CD4+ T-cells decreased from 35% for patients with 2 prior lines (n=18) to 30% with 3 (n=33), 23% with 4 and 20% with ≥5 prior lines of treatment (n=27), whilst the % of CD8+ cells were similar, indicating potential differential cumulative effects of anti-myeloma therapy on T-cell populations. We compared changes in T-cell profiles longitudinally over trial treatment from baseline to C1D14 and C4D14 with summary statistics. Overall, there was a marked increase in activated (HLA-DR+) T-cells with therapy, with a 2-fold increase in mean proportion of activated CD4+ and CD8+ from 3.9% and 10.2% at baseline to 7.8% and 19.9% at C1D14 and 7.2% and 28.2% at C4D14, respectively (Figure 1). Trial treatment was associated with a shift in sub-populations within CD8+ T-cells in particular, with a relative % decrease in naïve (CD45RA+) sub-populations and increase in memory (CD45RA-) populations. To identify differences associated with cyclophosphamide treatment a regression analysis was conducted on the C1D14 time point accounting for the treatment a patient received and incorporating their baseline (C1D1) measurement. The mean% estimates for total T-cells (CD3+) at C1D14 were significantly higher for the CPd arm in comparison to Pd: 72.1% [95% CI: 66.5 - 73.6] vs. 64.2% [58.2 - 66.1] (P=0.004). Estimates for the Pd arm appeared similar to baseline [mean C1D1: 61.7%]. Mean% estimates for CD8+ and CD4+ cells were also significantly higher with CPd treatment at C1D14 compared to Pd: 37.2% [32.6 - 38.0] vs. 33.1% [28.5 - 33.7] (P=0.03) and 26.2% [21.6 - 27.0] vs. 21.8% [21.6 - 27.0] (P=0.016), respectively. Importantly, mean% estimates for activated (HLA-DR+) CD4+ cells were significantly higher for the CPd arm 10.1% [6.9 - 9.4] vs 8.1% [5.1 - 7.2] in the Pd arm (P =0.02). There was a trend for additional increase of activated CD8+ cells by addition of cyclophosphamide to Pd therapy (P=0.06). Discussion We demonstrate for the first time in a randomised trial using systematic longitudinal immune profiling that addition of cyclophosphamide to pomalidomide and dexamethasone is significantly associated with altered T-cell profiles and an increased proportion of activated T-cells. MUKseven clinical endpoint data are reported separately, with improved response rates observed for CPd vs. Pd. Correlation of immune profiles with clinical outcomes and tumour genetics will be presented at the conference when PFS outcome data will be mature. Disclosures Boyd: Novartis: Consultancy, Honoraria; Janssen: Honoraria, Other: Travel and Accommodation expenses; Celgene: Consultancy, Honoraria, Other: Advisory role. Garg:Janssen: Honoraria; Novartis: Other: travel support, Research Funding; Takeda: Other: Travel Grant; Amgen: Honoraria, Other: Travel Support. Pawlyn:Janssen: Honoraria, Other: Travel support; Celgene Corporation: Consultancy, Honoraria, Other: Travel support; Amgen: Consultancy, Honoraria, Other: Travel Support; Takeda Oncology: Consultancy, Other: Travel support. Pierceall:Celgene: Employment, Equity Ownership. Cook:Celgene Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Glycomimetics: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Seattle Genetics: Honoraria; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau. Thakurta:Celgene Corporation: Employment, Equity Ownership. Kaiser:Chugai: Consultancy; Takeda: Consultancy, Other: travel support; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Other: travel support; Amgen: Consultancy, Honoraria.

In the original publication of the article, a part of acknowledgement section was missed out. The omitted acknowledgement is given below: 'The study was coordinated by the Imperial Clinical Trials Unit—Cancer, Imperial College London and Sponsored by Imperial College London. The Imperial Clinical Trials Unit receives funding from the National Institute for Health (NIHR) Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. This study was supported by Imperial Experimental Cancer Medicine Centre and Cancer Research UK Imperial Centre'.

Background: Parenting programmes are recommended for conduct disorders in 5–11 year olds, but ineffective for 25–33%. A feasibility trial was needed to determine whether a confirmatory trial of second-line, manualised short-term psychoanalytic child psychotherapy (mPCP) versus treatment as usual (TaU) is practicable.Method: This was a two-arm, pragmatic, parallel-group, multi-centre, individually-randomised controlled feasibility trial with blinded outcome assessment. Child–primary carer dyads were recruited from National Health Service Child and Adolescent Mental Health Services and mPCP delivered by routine child psychotherapists.Results: Thirty-two dyads (50% of eligible, 95% CI 37 to 63%) were recruited, with 16 randomised to each arm. Eleven (69%) completed ≥50% of 12 week mPCP and 13 (81%) ≥1 session. Follow-up was obtained for 24 (75%) at 4 months and 14/16 (88%) at 8 months. Teacher follow-up was 16 (50%). Manual adherence was good. Baseline candidate primary outcomes were 37.4 (SD 11.4) and 18.1 (SD 15.7) on the Child Behaviour Checklist/Teacher Report Form externalising scale and 102.8 (SD 28.4) and 58.8 (SD 38.9) on the total score. Health economics data collection was feasible and the trial acceptable to participants. Conclusion: Recruitment, teacher follow-up and the manual need some refinement. A confirmatory trial is feasible, subject to funding of research child psychotherapists.

e23140 Background: The steroid sulfatase (STS) pathway is involved in oestrogen biosynthesis. Irosustat is a 1st generation, orally active, irreversible STS inhibitor. Changes in the expression of the proliferation marker Ki67 in the context of perioperative studies in estrogen-receptor positive (ER+) early breast cancer (EBC) has been shown to be closely linked with relapse free survival. 3’-deoxy-3’-[18F] fluorothymidine (FLT) is a nucleoside analogue developed as a PET radiotracer for imaging proliferation; FLT uptake has been shown to correlate with tumour cell proliferation. We conducted a perioperative study in ER+ EBC to examine the changes in FLT uptake and Ki67 expression.Our study was designed to test the hypothesis that inhibition of STS with Irosustat for 2 weeks can result in a significant decrease in FLT uptake and therefore, tumour proliferation. Methods: Postmenopausal women with untreated ER+ EBC were recruited, and following a baseline FLT-PET scan received Irosustat (40mg once daily) for at least 2 weeks with a subsequent on treatment FLT-PET scan. The primary endpoint was change in FLT uptake, and other endpoints included safety and tolerability, changes in Ki-67, and expression of intratumoural steroidogenic enzymes and levels of circulating steroid hormone. Results: Between 11/2012 and 11/2014 13 women were recruited, and 10 started Irosustat treatment, followed by a repeat FLT-PET scan (N = 8). The median % changes in SUV and Ki from pre to post treatment were -0.4 (-29.9-48.2) and -7.1 (-62-193), respectively. Defining response as decreases of ≥ 20% in SUV and ≥ 30% in Ki, we observed responses in 1 (12.5% (95%CI 2-47%, p = 0.001)) and 3 (43% (95%CI 16-75%, p = < 0.001) patients respectively. The median % difference in Ki67 from pre to post treatment was 52.3% (p = 0.028). All adverse events were CTCAE Grade ≤ 2, with the most common grade 2 AE being an abnormal ECG. Pharmacodynamic data will be presented. Conclusions: Irosustat treatment resulted in a significant reduction in FLT uptake as well as Ki67, and is well tolerated. These data are the first demonstrating clinical activity of Irosustat in EBC, larger studies are needed. Clinical trial information: NCT01662726.

BACKGROUNDIntergroup 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 METHODSPrimary 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.RESULTSNeither 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.CONCLUSIONIn 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.

Neoadjuvant endocrine therapy is an alternative to chemotherapy for women with oestrogen receptor (ER)-positive early breast cancer (BC). We aimed to assess feasibility of recruiting patients to a study comparing chemotherapy versus endocrine therapy in postmenopausal women with ER-rich primary BC, and response as well as translational endpoints were assessed. Patients requiring neoadjuvant therapy were randomised to chemotherapy: 6 × 3-weekly cycles FE100C or endocrine therapy: letrozole 2.5 mg, daily for 18–23 weeks. Primary endpoints were recruitment feasibility and tissue collection. Secondary endpoints included clinical, radiological and pathological response rates, quality of life and translational endpoints. 63/80 patients approached were eligible, of those 44 (70, 95 % CI 57–81) were randomised. 12 (54.5, 95 % CI 32.2–75.6) chemotherapy patients showed radiological objective response compared with 13 (59.1, 95 % CI 36.4–79.3) letrozole patients. Compared with baseline, mean Ki-67 levels fell in both groups at days 2–4 and at surgery [fold change: 0.24 (95 % CI 0.12–0.51) and 0.24; (95 % CI 0.15–0.37), respectively]. Plasma total cfDNA levels rose from baseline to week 8 [fold change: chemotherapy 2.10 (95 % CI 1.47–3.00), letrozole 1.47(95 % CI 0.98–2.20)], and were maintained at surgery in the chemotherapy group [chemotherapy 2.63; 95 % CI 1.56–4.41), letrozole 0.95 (95 % CI 0.71–1.26)]. An increase in plasma let-7a miRNA was seen at surgery for patients with objective radiological response to chemotherapy. Recruitment and tissue collection endpoints were met; however, a larger trial was deemed unfeasible due to slow accrual. Both regimens were equally efficacious. Dynamic changes were seen in Ki-67 and circulating biomarkers in both groups with increases in cfDNA and let-7a miRNA persisting until surgery for chemotherapy patients.

IES, a randomised study in 4724 postmenopausal patients (pts) with ER + /unknown early breast cancer, showed a survival benefit from switching adjuvant endocrine therapy [2-3 years tamoxifen (T) to exemestane (E)]. PathIES a retrospective translational study assessed if biomarkers can predict response to continuing on T or switching to E. Central assessment of ER, PR, HER2, Ki67 & ERβ1 was conducted on 1256 FFPE primary tumour samples (27% pts). Biomarker expression was measured by IHC. HER2 was confirmed by FISH if ≥IHC2+. ERβ1 was dichotomised at the median. Tumours were deemed positive for ER/PR if IHC ≥1% or Allred ≥3 & for HER2 if IHC 3+ or if FISH amplified. Ki67 was high if > 11% LI (median). Primary endpoints were DFS & OS. Proportional hazards models & interaction tests explored the differential effects of each marker with treatment (trt). Time-to-distant recurrence was used to test the prognostic value of IHC4. Characteristics & trt allocation were comparable to those pts without tumour sample apart from prior chemotherapy (CT) & HRT use. 19% of pts with tumour sample and 37% of pts without had prior CT [p < 0.001], whilst 31% of pts with tumour sample and 14% of pts without had received HRT [p < 0.001]. High IHC4 score was associated with worse prognosis in T & E [2nd tertile v 1st tertile HR 1.4 95%CI (0.7-2.9), 3rd tertile v 1st tertile HR 2.3 95%CI (1.1-4.7), p = 0.04]. Addition of clinical variables to IHC4 made the effect more profound. When adjusting for nodal status, age group, prior CT & HRT use, histological type & grade, HER2, ER, PR & Ki67, high ERβ1 expression was predictive for continued T benefit [DFS HR 0.4 95%CI(0.2-0.7) interaction p = 0.01, OS HR 0.4 95%CI(0.2-0.7) interaction p = 0.004]. High PR expression was associated with significant improvement in DFS for T [HR 0.3 95%CI (0.1-0.7)]. High Ki67 expression was associated with worse prognosis in T & E [HR 1.7 95%CI (1.1-2.7)]. PathIES confirmed the prognostic value of IHC4. High ERβ1/PR expression was associated with improved DFS & OS for T. Results suggest pts with high ERβ1/PR expression should receive 5 years of T rather than switch to E. As this is the first time ERβ1 was examined in the context of a trial, results require independent validation.Disclosure: J. Bliss: Grant income from PfizerR.C. Coombes: Grant income from PfizerAll other authors have declared no conflicts of interest. IES, a randomised study in 4724 postmenopausal patients (pts) with ER + /unknown early breast cancer, showed a survival benefit from switching adjuvant endocrine therapy [2-3 years tamoxifen (T) to exemestane (E)]. PathIES a retrospective translational study assessed if biomarkers can predict response to continuing on T or switching to E. Central assessment of ER, PR, HER2, Ki67 & ERβ1 was conducted on 1256 FFPE primary tumour samples (27% pts). Biomarker expression was measured by IHC. HER2 was confirmed by FISH if ≥IHC2+. ERβ1 was dichotomised at the median. Tumours were deemed positive for ER/PR if IHC ≥1% or Allred ≥3 & for HER2 if IHC 3+ or if FISH amplified. Ki67 was high if > 11% LI (median). Primary endpoints were DFS & OS. Proportional hazards models & interaction tests explored the differential effects of each marker with treatment (trt). Time-to-distant recurrence was used to test the prognostic value of IHC4. Characteristics & trt allocation were comparable to those pts without tumour sample apart from prior chemotherapy (CT) & HRT use. 19% of pts with tumour sample and 37% of pts without had prior CT [p < 0.001], whilst 31% of pts with tumour sample and 14% of pts without had received HRT [p < 0.001]. High IHC4 score was associated with worse prognosis in T & E [2nd tertile v 1st tertile HR 1.4 95%CI (0.7-2.9), 3rd tertile v 1st tertile HR 2.3 95%CI (1.1-4.7), p = 0.04]. Addition of clinical variables to IHC4 made the effect more profound. When adjusting for nodal status, age group, prior CT & HRT use, histological type & grade, HER2, ER, PR & Ki67, high ERβ1 expression was predictive for continued T benefit [DFS HR 0.4 95%CI(0.2-0.7) interaction p = 0.01, OS HR 0.4 95%CI(0.2-0.7) interaction p = 0.004]. High PR expression was associated with significant improvement in DFS for T [HR 0.3 95%CI (0.1-0.7)]. High Ki67 expression was associated with worse prognosis in T & E [HR 1.7 95%CI (1.1-2.7)]. PathIES confirmed the prognostic value of IHC4. High ERβ1/PR expression was associated with improved DFS & OS for T. Results suggest pts with high ERβ1/PR expression should receive 5 years of T rather than switch to E. As this is the first time ERβ1 was examined in the context of a trial, results require independent validation. Disclosure: J. Bliss: Grant income from Pfizer R.C. Coombes: Grant income from Pfizer All other authors have declared no conflicts of interest.

INTRODUCTION:Mammographic breast density is one of the strongest known risk factors for breast cancer. We present a novel technique for estimating breast density based on 3D T1-weighted Magnetic Resonance Imaging (MRI) and evaluate its performance, including for breast cancer risk prediction, relative to two standard mammographic density-estimation methods. METHODS:The analyses were based on MRI (n = 655) and mammography (n = 607) images obtained in the course of the UK multicentre magnetic resonance imaging breast screening (MARIBS) study of asymptomatic women aged 31 to 49 years who were at high genetic risk of breast cancer. The MRI percent and absolute dense volumes were estimated using our novel algorithm (MRIBview) while mammographic percent and absolute dense area were estimated using the Cumulus thresholding algorithm and also using a 21-point Visual Assessment scale for one medio-lateral oblique image per woman. We assessed the relationships of the MRI and mammographic measures to one another, to standard anthropometric and hormonal factors, to BRCA1/2 genetic status, and to breast cancer risk (60 cases) using linear and Poisson regression. RESULTS:MRI percent dense volume is well correlated with mammographic percent dense area (R = 0.76) but overall gives estimates 8.1 percentage points lower (P < 0.0001). Both show strong associations with established anthropometric and hormonal factors. Mammographic percent dense area, and to a lesser extent MRI percent dense volume were lower in BRCA1 carriers (P = 0.001, P = 0.010 respectively) but there was no association with BRCA2 carrier status. The study was underpowered to detect expected associations between percent density and breast cancer, but women with absolute MRI dense volume in the upper half of the distribution had double the risk of those in the lower half (P = 0.009). CONCLUSIONS:The MRIBview estimates of volumetric breast density are highly correlated with mammographic dense area but are not equivalent measures; the MRI absolute dense volume shows potential as a predictor of breast cancer risk that merits further investigation.

PURPOSE:A method and computer tool to estimate percentage magnetic resonance (MR) imaging (MRI) breast density using three-dimensional T(1)-weighted MRI is introduced, and compared with mammographic percentage density [X-ray mammography (XRM)]. MATERIALS AND METHODS:Ethical approval and informed consent were obtained. A method to assess MRI breast density as percentage volume occupied by water-containing tissue on three-dimensional T(1)-weighted MR images is described and applied in a pilot study to 138 subjects who were imaged by both MRI and XRM during the Magnetic Resonance Imaging in Breast Screening study. For comparison, percentage mammographic density was measured from matching XRMs as a ratio of dense to total projection areas scored visually using a 21-point score and measured by applying a two-dimensional interactive program (CUMULUS). The MRI and XRM percent methods were compared, including assessment of left-right and interreader consistency. RESULTS:Percent MRI density correlated strongly (r = 0.78; P < 0.0001) with percent mammographic density estimated using Cumulus. Comparison with visual assessment also showed a strong correlation. The mammographic methods overestimate density compared with MRI volumetric assessment by a factor approaching 2. DISCUSSION:MRI provides direct three-dimensional measurement of the proportion of water-based tissue in the breast. It correlates well with visual and computerized percent mammographic density measurements. This method may have direct application in women having breast cancer screening by breast MRI and may aid in determination of risk.