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Background Ovarian carcinosarcoma (OCS) is an uncommon, biphasic and highly aggressive ovarian cancer type, which has received relatively little research attention. Methods We curated the largest pathologically confirmed OCS cohort to date, performing detailed histopathological characterisation, analysis of features associated with survival and comparison against high-grade serous ovarian carcinoma (HGSOC). Results Eighty-two OCS patients were identified; overall survival was poor (median 12.7 months). In all, 79% demonstrated epithelial components of high-grade serous (HGS) type, while 21% were endometrioid. Heterologous elements were common (chondrosarcoma in 32%, rhabdomyosarcoma in 21%, liposarcoma in 2%); chondrosarcoma was more frequent in OCS with endometrioid carcinomatous components. Earlier stage, complete resection and platinum-containing adjuvant chemotherapy were associated with prolonged survival; however, risk of relapse and mortality was high across all patient groups. Histological subclassification did not identify subgroups with distinct survival. Compared to HGSOC, OCS patients were older (P P = 0.025), demonstrated lower chemotherapy response rate (P = 0.001) and had significantly poorer survival (P Conclusion OCS represents a distinct, highly lethal form of ovarian cancer for which new treatment strategies are urgently needed. Histological subclassification does not identify patient subgroups with distinct survival. Aggressive adjuvant chemotherapy should be considered for all cases, including those with early-stage disease.

BACKGROUND: Low-grade serous carcinoma of the ovary or peritoneum is characterised by MAPK pathway aberrations and its reduced sensitivity to chemotherapy relative to high-grade serous carcinoma. We compared the MEK inhibitor trametinib to physician's choice standard of care in patients with recurrent low-grade serous carcinoma. METHODS: This international, randomised, open-label, multicentre, phase 2/3 trial was done at 84 hospitals in the USA and UK. Eligible patients were aged 18 years or older with recurrent low-grade serous carcinoma and measurable disease, as defined by Response Evaluation Criteria In Solid Tumors version 1.1, had received at least one platinum-based regimen, but not all five standard-of-care drugs, and had received an unlimited number of previous regimens. Patients with serous borderline tumours or tumours containing low-grade serous and high-grade serous carcinoma were excluded. Eligible patients were randomly assigned (1:1) to receive either oral trametinib 2 mg once daily (trametinib group) or one of five standard-of-care treatment options (standard-of-care group): intravenous paclitaxel 80 mg/m2 by body surface area on days 1, 8, and 15 of every 28-day cycle; intravenous pegylated liposomal doxorubicin 40-50 mg/m2 by body surface area once every 4 weeks; intravenous topotecan 4 mg/m2 by body surface area on days 1, 8, and 15 of every 28-day cycle; oral letrozole 2·5 mg once daily; or oral tamoxifen 20 mg twice daily. Randomisation was stratified by geographical region (USA or UK), number of previous regimens (1, 2, or ≥3), performance status (0 or 1), and planned standard-of-care regimen. The primary endpoint was investigator-assessed progression-free survival while receiving randomised therapy, as assessed by imaging at baseline, once every 8 weeks for 15 months, and then once every 3 months thereafter, in the intention-to-treat population. Safety was assessed in patients who received at least one dose of study therapy. This trial is registered with ClinicalTrials.gov, NCT02101788, and is active but not recruiting. FINDINGS: Between Feb 27, 2014, and April 10, 2018, 260 patients were enrolled and randomly assigned to the trametinib group (n=130) or the standard-of-care group (n=130). At the primary analysis, there were 217 progression-free survival events (101 [78%] in the trametinib group and 116 [89%] in the standard-of-care group). Median progression-free survival in the trametinib group was 13·0 months (95% CI 9·9-15·0) compared with 7·2 months (5·6-9·9) in the standard-of-care group (hazard ratio 0·48 [95% CI 0·36-0·64]; p

SV loads in non-BRCA1/2 HR genes per sample by SV type

Supplementary Data from Multiomic Characterization of High-Grade Serous Ovarian Carcinoma Enables High-Resolution Patient Stratification

Purpose:The abundance and effects of structural variation at BRCA1/2 in tumors are not well understood. In particular, the impact of these events on homologous recombination repair deficiency (HRD) has yet to be demonstrated.Experimental Design:Exploiting a large collection of whole-genome sequencing data from high-grade serous ovarian carcinoma (N = 205) together with matched RNA sequencing for the majority of tumors (N = 150), we have comprehensively characterized mutation and expression at BRCA1/2.Results:In addition to the known spectrum of short somatic mutations (SSM), we discovered that multi-megabase structural variants (SV) were a frequent, unappreciated source of BRCA1/2 disruption in these tumors, and we found a genome-wide enrichment for large deletions at the BRCA1/2 loci across the cohort. These SVs independently affected a substantial proportion of patients (16%) in addition to those affected by SSMs (24%), conferring HRD and impacting patient survival. We also detail compound deficiencies involving SSMs and SVs at both loci, demonstrating that the strongest risk of HRD emerges from combined SVs at both BRCA1 and BRCA2 in the absence of SSMs. Furthermore, these SVs are abundant and disruptive in other cancer types.Conclusions:These results extend our understanding of the mutational landscape underlying HRD, increase the number of patients predicted to benefit from therapies exploiting HRD, and suggest there is currently untapped potential in SV detection for patient stratification.

Supplementary methods and supplementary figures

Background: Ovarian carcinosarcoma (OCS) is the most aggressive ovarian cancer type. Risk of relapse and death is high across all patient groups, including those diagnosed at early stage. OCS is biphasic, comprising both carcinomatous and sarcomatous populations, leading to its historic consideration alongside true sarcomas. However, we now recognize that OCS in fact represent metaplastic carcinomas, with the sarcomatous component having undergone complete epithelial to mesenchymal transition (EMT) from carcinoma. Detailed understanding of shared and compartment-specific OCS biology has the potential to identify therapeutic opportunities to improve patient survival. Methods: We recently curated the largest pathologically-confirmed OCS cohort to date. Here, we perform compartment-specific profiling of 12 cases by mRNA sequencing, whole exome sequencing, microRNA (miRNA) profiling and quantification of tumor-infiltrating lymphocytes. These data paint a detailed picture of shared and compartment-specific biology between matched carcinomatous and sarcomatous compartments. Results: The sarcomatous compartments harbored significantly fewer infiltrating CD8+ cells (P=0.006), with a significantly lower CD8+:CD3+ cell ratio compared to the carcinomatous components (P=0.002). In 11 of 12 cases, identical TP53 mutations were identified in both cell populations; the remaining case was TP53 wild-type in both compartments. Paired analysis of mRNA sequencing identified 1477 significantly differentially expressed transcripts at FDR Conclusions: Carcinomatous and sarcomatous compartments of OCS demonstrate marked differences in transcriptomic profiles, immune engagement and miRNA expression patterns. Identification of shared TP53 mutations between compartments supports the notion that OCS represent metaplastic carcinomas. Shared biological events represent opportunities for targeted interventions that may be efficacious against both cell populations, while compartment-specific biological events allude to mechanisms by which the carcinomatous population undergoes EMT to form the sarcomatous compartment. Citation Format: Robert L. Hollis, Ailsa Oswald, Lorna J. Stillie, Ian Croy, Michael Churchman, Charlie Gourley, C. Simon Herrington. Compartment-specific multiomic characterisation of ovarian carcinosarcoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6076.

OBJECTIVE Investigate the clinical landscape of ovarian carcinoma (OC) over time. DESIGN Register-based prospectively collected data. SETTING South East Scotland. SAMPLE A total of 2805 OC patients diagnosed in 1981-2015. METHODS Survival times were visualised using the Kaplan-Meier method; median survival, 5-year survival probabilities and associated restricted mean survival time analyses were used to quantify survival differences. MAIN OUTCOME MEASURES Disease-specific survival. RESULTS A significant increase in disease-specific survival (DSS) from 1981-1985 to 2011-2015 was observed (median 1.73 versus 4.23 years, P

BackgroundLow-grade serous ovarian carcinoma (LGSOC) is a distinct, under-investigated and relatively chemotherapy-resistant ovarian cancer type. Understanding the molecular landscape is crucial to maximise the impact of molecularly-targeted therapy.MethodsWhole exome sequencing and copy number data were integrated with histopathological patterns, ER/PR expression, and detailed clinical annotation, including survival, in a carefully curated LGSOC cohort.Results63 tumours were analysed in the largest comprehensive genomic LGSOC study to date. Three genomic subgroups were identified: canonical MAPK mutant (cMAPKm: 52%, KRAS/BRAF/NRAS), MAPK-associated mutation (27%, 14 MAPK-associated genes) and MAPK wild-type (MAPKwt: 21%). MAPKwt patients were younger at diagnosis (median 47 versus 62 years in the cMAPKm subgroup) and demonstrated shorter survival [multivariable HR (mHR) 4.17]. The inferior survival in the MAPKwt subgroup was due to shorter post-relapse survival (mHR 5.22) rather than shorter time to first progression (mHR 1.15). Patients in the MAPK-associated mutation subgroup had similar survival to cMAPKm cases. The cMAPKm subgroup more frequently demonstrated macropapillary invasion. Desmoplasia and micropapillary invasion were independently associated with poor survival. NOTCH pathway activation occurred independently of MAPK subgroup.ConclusionsLGSOC comprises multiple genomic subgroups with distinct clinical, molecular and histopathological features. True MAPKwt cases represent around a fifth of patients: they are younger but have poorer survival. New therapeutic strategies with activity in this subgroup are urgently required. NOTCH inhibitors represent a therapeutic strategy worthy of exploration.

BackgroundHigh grade serous ovarian carcinoma (HGSOC) is the most common type of ovarian cancer; most patients experience disease recurrence which accumulates chemoresistance, leading to treatment failure. Previous investigations have characterised HGSOC at the genomic and transcriptomic level, identifying subtypes of patients with differential outcome and treatment response. However, the relationship between molecular events identified at the gene sequence, gene copy number and gene expression levels remains poorly defined.MethodsWe perform multi-layer molecular characterisation of a large retrospective HGSOC cohort (n=362) with detailed clinical annotation to interrogate the relationship between patient groups defined by gene mutation, copy number events, gene expression patterns and infiltrating immune cell burden. We construct a high resolution picture of the molecular landscape in HGSOC and identify features of tumours associated with distinct clinical behaviour in patients.ResultsBRCA2-mutant (BRCA2m) andEMSY-overexpressing cases demonstrated prolonged survival (multivariable hazard ratio 0.40 and 0.53) and higher chemotherapy response rates at first- and second-line treatment.CCNE1-gained (CCNE1g) cases demonstrated shorter survival (multivariable hazard ratio 1.52, 95% CI 1.10-2.10), under-representation of FIGO stage IV cases (P=0.017) and no significant difference in treatment response. We demonstrate marked overlap between the TCGA- and derived subtypes: the TCGA DIF, IMR, PRO and MES subtypes correlated with the Tothill C4, C2, C5 and C1 subtypes (PBRCA1/2m frequency (25.5% and 32.5%) and significantly greater infiltration of immune cells (PCCNE1g rate (23.9% and 22.2%) and were uniformly low in immune cell infiltration. The survival benefit for cases with aberrations in homologous recombination repair (HRR) genes was apparent across all transcriptomic subtypes (hazard ratio range 0.48-0.68). There was significant co-occurrence of RB loss and HRR gene aberrations (P=0.005); RB loss was further associated with favourable survival within cases harbouring HRR aberrations (multivariable hazard ratio 0.50, 95% CI 0.30-0.84).ConclusionsThese data paint a high resolution picture of the molecular landscape in HGSOC, better defining patients who may benefit most from specific molecular therapeutics and highlighting those for whom novel treatment strategies are needed to improve outcomes.

Ovarian carcinoma (OC) is an umbrella term for multiple distinct diseases (histotypes), each with their own developmental origins, clinical behaviour and molecular profile. Accordingly, OC management is progressing away from a one-size-fits all approach, toward more molecularly-driven, histotype-specific management strategies. Our knowledge of driver events in high grade serous OC, the most common histotype, has led to major advances in treatments, including PARP inhibitor use. However, these agents are not suitable for all patients, most notably for many of those with rare OC histotypes. Identification of additional targeted therapeutic strategies will require a detailed understanding of the molecular landscape in each OC histotype. Until recently,tumour profiling studies in rare histotypes were sparse; however, significant advances have been made over the last decade. In particular, reports of genomic characterisation in endometrioid, clear cell, mucinous and lowgrade serous OC have significantly expanded our understanding of mutational events in these tumour types. Nonetheless, substantial knowledge gaps remain. This review summarises our current understanding of each histotype, highlighting recent advances in these unique diseases and outlining immediate research priorities for accelerating progress toward improving patient outcomes

Simple Summary Mucinous ovarian carcinoma (MOC) is a unique type of ovarian cancer. While many MOC patients have excellent survival, patients who experience recurrence have extremely poor prognosis. Identifying patients at the highest risk of recurrence is important for identifying which patients need the most aggressive treatment, and to identify where new treatment strategies are needed to improve survival. We use a large cohort of MOC patients to identify factors associated with high and low risk of recurrence. We show that once patients reach 5 years from diagnosis, their risk of recurrence is low. Patients with more advanced-stage disease and higher pathological grade of disease are more likely to experience recurrence, and their survival is significantly shorter. For early-stage MOC patients, survival time was similar whether they were treated with surgery plus chemotherapy, or whether they only had surgery. Patient survival time following recurrence is extremely poor (median 5 months); new treatment options are urgently needed to improve their survival. Abstract Mucinous ovarian carcinoma (MOC) is a unique form of ovarian cancer. MOC typically presents at early stage but demonstrates intrinsic chemoresistance; treatment of advanced-stage and relapsed disease is therefore challenging. We harness a large retrospective MOC cohort to identify factors associated with recurrence risk and survival. A total of 151 MOC patients were included. The 5 year disease-specific survival (DSS) was 84.5%. Risk of subsequent recurrence after a disease-free period of 2 and 5 years was low (8.3% and 5.6% over the next 10 years). The majority of cases were FIGO stage I (35.6% IA, 43.0% IC). Multivariable analysis identified stage and pathological grade as independently associated with DSS (p < 0.001 and p < 0.001). Grade 1 stage I patients represented the majority of cases (53.0%) and demonstrated exceptional survival (10 year DSS 95.3%); survival was comparable between grade I stage IA and stage IC patients, and between grade I stage IC patients who did and did not receive adjuvant chemotherapy. At 5 years following diagnosis, the proportion of grade 1, 2 and 3 patients remaining disease free was 89.5%, 74.9% and 41.7%; the corresponding proportions for FIGO stage I, II and III/IV patients were 91.1%, 76.7% and 19.8%. Median post-relapse survival was 5.0 months. Most MOC patients present with low-grade early-stage disease and are at low risk of recurrence. New treatment options are urgently needed to improve survival following relapse, which is associated with extremely poor prognosis.

Background Numerous studies have investigated the association between hormone receptor expression and clinical outcome in ovarian carcinoma (OC); however, these have largely focussed on serous OCs, with few studies reporting specifically on endometrioid OCs (EnOC). Where analyses have been stratified by histotype, expression has been assessed using the percentage of positive tumor cells, without accounting for nuclear expression intensity. Methods Here we assess the expression levels of progesterone receptor (PR), estrogen receptor alpha (ER) and androgen receptor (AR) using histoscore – a nuclear scoring method incorporating both proportion of positive cells and the intensity of nuclear staining – across a cohort of 107 WT1 negative EnOCs. Results Hierarchical clustering by PR, ER and AR histoscores identified four EnOC subgroups (PR+/ER+, PR+/ER−, PR−/ER+ and PR−/ER−). EnOC patients in the PR+/ER+ and PR+/ER− groups displayed favorable outcome (multivariable HR for disease-specific survival 0.05 [0.01–0.35] and 0.05 [0.00–0.51]) compared to the PR−/ER+ group. Ten-year survival for stage II PRhigh and PRlow cases was 94.1% and 42.4%. ERhigh EnOC patients (PR+/ER+, PR−/ER+) had higher body mass index compared to ERlow cases (P = 0.015) and high grade serous OC patients (P, Highlights • We identify four subgroups of endometrioid ovarian carcinoma (EnOC) defined by hormone receptor expression patterns. • EnOC patients in the PRhigh (PR+/ER+, PR+/ER−) groups demonstrate markedly favorable outcome. • Stage II EnOC patients in the PRhigh groups display a ten-year survival of approximately 95%. • ERhigh (PR+/ER+, PR−/ER+) EnOC patients had a higher body mass index vs ERlow cases and high grade serous carcinoma patients.

Endometrioid ovarian carcinoma (EnOC) is an under-investigated ovarian cancer type. Recent studies have described disease subtypes defined by genomics and hormone receptor expression patterns; here, we determine the relationship between these subtyping layers to define the molecular landscape of EnOC with high granularity and identify therapeutic vulnerabilities in high-risk cases. Whole exome sequencing data were integrated with progesterone and oestrogen receptor (PR and ER) expression-defined subtypes in 90 EnOC cases following robust pathological assessment, revealing dominant clinical and molecular features in the resulting integrated subtypes. We demonstrate significant correlation between subtyping approaches: PR-high (PR + /ER + , PR + /ER−) cases were predominantly CTNNB1-mutant (73.2% vs 18.4%, P TP53 mutation frequency (38.8% vs 7.3%, P = 0.001), greater genomic complexity (P = 0.007) and more frequent copy number alterations (P = 0.001). PR-high EnOC patients experience favourable disease-specific survival independent of clinicopathological and genomic features (HR = 0.16, 95% CI 0.04–0.71). TP53 mutation further delineates the outcome of patients with PR-low tumours (HR = 2.56, 95% CI 1.14–5.75). A simple, routinely applicable, classification algorithm utilising immunohistochemistry for PR and p53 recapitulated these subtypes and their survival profiles. The genomic profile of high-risk EnOC subtypes suggests that inhibitors of the MAPK and PI3K-AKT pathways, alongside PARP inhibitors, represent promising candidate agents for improving patient survival. Patients with PR-low TP53-mutant EnOC have the greatest unmet clinical need, while PR-high tumours—which are typically CTNNB1-mutant and TP53 wild-type—experience excellent survival and may represent candidates for trials investigating de-escalation of adjuvant chemotherapy to agents such as endocrine therapy.

Introduction/Background Niraparib is an oral, highly selective poly(ADP-ribose) polymerase inhibitor (PARPi). The PRIMA/ENGOT-OV26/GOG-3012 trial intention-to-treat population included stage III and IV ovarian cancer (OC) patients post-primary or interval debulking surgery (PDS/IDS) irrespective of residual disease (visible residual disease [VRD] or no VRD [NVRD]), except for stage III patients post-PDS with NVRD. A data gap therefore exists in the stage III post-PDS NVRD population. This study aims to use real-world evidence from the Edinburgh Ovarian Cancer Database to explore the difference in overall survival (OS) and progression-free survival (PFS) in: a) a ‘simulated-PRIMA cohort’ (stage III VRD after PDS, stage III and IDS, and stage IV OC), b) a ‘simulated-NVRD after PDS cohort’ (stage III NVRD after PDS) and c) a larger ‘simulated-broader cohort’ (both cohorts a and b plus the additional stage III non-evaluable debulking status cases). Methodology A retrospective observational study was conducted to examine characteristics and long-term outcomes for patients diagnosed with advanced OC within the Edinburgh Cancer Centre between 1 January 2000 and 31 December 2015. Patients were followed until their last patient record or last data cut (January 2019) and were chosen to match the three defined populations. Main outcomes were OS and PFS, the latter defined as time from diagnosis to first progression as defined by radiology, tumour marker (CA125) or the treating physician where other investigations were not evaluable. Results Baseline patient characteristics in the simulated-PRIMA (n=472), simulated-stage III NVRD after PDS (n=69) and simulated-broader (n=569) cohorts matched the PRIMA trial in most categories. PFS and OS for simulated cohorts are shown in the table 1. When compared with the simulated-PRIMA cohort, the simulated-stage III NVRD after PDS cohort had significantly longer PFS (hazard ratio [HR]=0.43, 95% CI 0.32–0.58, P Conclusion The simulated-broader cohort showed longer duration of OS and PFS outcomes as the survival curves lie above the simulated-PRIMA cohort. This difference is driven by the better prognosis for patients with stage III NVRD after PDS population; this population accounted for approximately 17% of the contemporary patient cohort at this UK centre. Disclosures This study was funded by GlaxoSmithKline. Clinical Trial Registration: N/A Dr. Hollis reports institutional grants and personal fees from GlaxoSmithKline. Dr. Gourley reports personal fees from Roche, Clovis, Tesaro, Foundation One, Nucana, Aprea, Novartis, Chugai, and MSD; institutional grants from Clovis, Tesaro, Nucana, and Novartis. Drs. Kiss, Roebuck, Heffernan and Starkie-Camejo are employees of GlaxoSmithKline.

PURPOSE: The abundance and effects of structural variation at BRCA1/2 in tumours are not well understood. In particular, the impact of these events on homologous recombination repair deficiency (HRD) has yet to be demonstrated. EXPERIMENTAL DESIGN: Exploiting a large collection of whole genome sequencing data from high grade serous ovarian carcinoma (N=205) together with matched RNA-seq for the majority of tumours (N=150), we have comprehensively characterised mutation and expression at BRCA1/2. RESULTS: In addition to the known spectrum of short somatic mutations (SSMs), we discover that multi-megabase structural variants (SVs) are a frequent, unappreciated source of BRCA1/2 disruption in these tumours, and we find a genome wide enrichment for large deletions at the BRCA1/2 loci across the cohort. These SVs independently affect a substantial proportion of patients (16%) in addition to those affected by SSMs (24%), conferring homologous recombination repair deficiency (HRD) and impacting patient survival. We also detail compound deficiencies involving SSMs and SVs at both loci, demonstrating that the strongest risk of HRD emerges from combined SVs at both BRCA1 and BRCA2 in the absence of SSMs. Further, these SVs are abundant and disruptive in other cancer types. CONCLUSIONS: These results extend our understanding of the mutational landscape underlying HRD, increase the number of patients predicted to benefit from therapies exploiting HRD, and suggest there is currently untapped potential in SV detection for patient stratification.

Clear cell carcinoma of the ovary has distinct biology and clinical behavior. There are significant geographical and racial differences in the incidence of clear cell carcinoma compared with other epithelial ovarian tumors. Patients with clear cell carcinoma are younger, tend to present at an early stage, and their tumors are commonly associated with endometriosis, which is widely accepted as a direct precursor of clear cell carcinoma and has been identified pathologically in approximately 50% of clear cell carcinoma cases. The most frequent and important specific gene alterations in clear cell carcinoma are mutations of AT-rich interaction domain 1A (ARID1A) (~50% of cases) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) (~50% cases). More broadly, subgroups of clear cell carcinoma have been identified based on C-APOBEC (apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like) and C-AGE (age-related) mutational signatures. Gene expression profiling shows upregulation of hepatocyte nuclear factor 1-beta (HNF1β) and oxidative stress-related genes, and has identified epithelial-like and mesenchymal-like tumor subgroups. Although the benefit of platinum-based chemotherapy is not clearly defined it remains the mainstay of first-line therapy. Patients with early-stage disease have a favorable clinical outcome but the prognosis of patients with advanced-stage or recurrent disease is poor. Alternative treatment strategies are required to improve patient outcome and the development of targeted therapies based on molecular characteristics is a promising approach. Improved specificity of the histological definition of this tumor type is helping these efforts but, due to the rarity of clear cell carcinoma, international collaboration will be essential to design appropriately powered, large-scale clinical trials.

Purpose of review: PARP inhibitors have transformed the management of BRCA mutant (BRCAmut) high-grade serous and endometroid ovarian cancer (HGOC). However, it is clear that the benefit can be extended beyond this subgroup, particularly to those cancers with homologous recombination repair deficiency (HRD). We review emerging molecular and clinical data to support the use of PARP inhibitors in HRD HGOC and discuss the advantages and disadvantages of different HRD assays. Recent findings: Several phase 3 trials support the use of PARP inhibitor maintenance therapy beyond those patients with BRCAmut in the first-line and platinum-sensitive relapse setting. Many of these studies included HRD testing and it is clear, regardless of the assay used, that an incremental reduction in benefit is observed from BRCAmut tumours to HRD to homologous recombination proficient tumours. However, although currently available HRD assays predict the magnitude of benefit from PARP inhibitors, they consistently fail to identify a subgroup of patients who do not benefit. Summary: Clinical data support the use of PARP inhibitor maintenance therapy beyond BRCAmut patients. Current HRD tests lack negative predictive value and more research is required to develop a composite HRD assay that provides a dynamic readout of HRD status.

The estrogen receptor (ER) has functionality in selected ovarian cancer subtypes and represents a potential target for therapy. The majority (>80%) of high grade serous, low grade serous and endometrioid carcinomas and many granulosa cell tumors express ER-alpha (ERα), and these tumor types have demonstrated responses to endocrine therapy (tamoxifen and aromatase inhibitors) in multiple clinical studies. Biomarkers of responses to these drugs are actively being sought to help identify responsive cancers. Evidence for both pro-proliferative and pro-migratory roles for ERα has been obtained in model systems. ER-beta (ERβ) is generally considered to have a tumor suppressor role in ovarian cancer cells, being associated with the repression of cell growth and invasion. The differential expression of the specific ERβ isoforms may determine functionality within ovarian cancer cells. The more recently identified G protein-coupled receptor (GPER1; GPR30) has been shown to mediate both tumor-suppressive and tumor-promoting action in ovarian cancer cells, suggesting a more complex role. This review will summarize recent findings in this field.

High grade serous ovarian cancer (HGSOC) is a major cause of female cancer mortality. The approval of poly (ADP-ribose) polymerase (PARP) inhibitors for clinical use has greatly improved treatment options for patients with homologous recombination repair (HRR)-deficient HGSOC, although the development of PARP inhibitor resistance in some patients is revealing limitations to outcome. A proportion of patients with HRR-proficient cancers also benefit from PARP inhibitor therapy. Our aim is to compare mechanisms of resistance to the PARP inhibitor olaparib in these two main molecular categories of HGSOC and investigate a way to overcome resistance that we considered particularly suited to a cancer like HGSOC, where there is a very high incidence of TP53 gene mutation, making HGSOC cells heavily reliant on the G2 checkpoint for repair of DNA damage and survival. We identified alterations in multiple factors involved in resistance to PARP inhibition in both HRR-proficient and -deficient cancers. The most frequent change was a major reduction in levels of poly (ADP-ribose) glycohydrolase (PARG), which would be expected to preserve a residual PARP1-initiated DNA damage response to DNA single-strand breaks. Other changes seen would be expected to boost levels of HRR of DNA double-strand breaks. Growth of all olaparib-resistant clones isolated could be controlled by WEE1 kinase inhibitor AZD1775, which inactivates the G2 checkpoint. Our work suggests that use of the WEE1 kinase inhibitor could be a realistic therapeutic option for patients that develop resistance to olaparib.

Endometrioid ovarian carcinoma (EnOC) demonstrates substantial clinical and molecular heterogeneity. Here, we report whole exome sequencing of 112 EnOC cases following rigorous pathological assessment. We detect a high frequency of mutation in CTNNB1 (43%), PIK3CA (43%), ARID1A (36%), PTEN (29%), KRAS (26%), TP53 (26%) and SOX8 (19%), a recurrently-mutated gene previously unreported in EnOC. POLE and mismatch repair protein-encoding genes were mutated at lower frequency (6%, 18%) with significant co-occurrence. A molecular taxonomy is constructed, identifying clinically distinct EnOC subtypes: cases with TP53 mutation demonstrate greater genomic complexity, are commonly FIGO stage III/IV at diagnosis (48%), are frequently incompletely debulked (44%) and demonstrate inferior survival; conversely, cases with CTNNB1 mutation, which is mutually exclusive with TP53 mutation, demonstrate low genomic complexity and excellent clinical outcome, and are predominantly stage I/II at diagnosis (89%) and completely resected (87%). Moreover, we identify the WNT, MAPK/RAS and PI3K pathways as good candidate targets for molecular therapeutics in EnOC., The molecular classification of endometroid ovarian carcinomas (EnOC) has not been established, preventing the development of stratified therapeutic approaches. Here the authors characterise the molecular landscape of EnOC by whole exome sequencing, identifying clinically distinct disease subtypes.

DATA AVAILABILITYThe mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD017117.; International audience; Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme with transamidating activity. We report here that both expression and activity of TG2 are enhanced in mammalian epithelial cells infected with the obligate intracellular bacteria Chlamydia trachomatis. Genetic or pharmacological inhibition of TG2 impairs bacterial development. We show that TG2 increases glucose import by up-regulating the transcription of the glucose transporter genes GLUT-1 and GLUT-3. Furthermore, TG2 activation drives one specific glucose-dependent pathway in the host, i.e., hexosamine biosynthesis. Mechanistically, we identify the glucosamine:fructose-6-phosphate amidotransferase (GFPT) among the substrates of TG2. GFPT modification by TG2 increases its enzymatic activity, resulting in higher levels of UDP-N-acetylglucosamine biosynthesis and protein O-GlcNAcylation. The correlation between TG2 transamidating activity and O-GlcNAcylation is disrupted in infected cells because host hexosamine biosynthesis is being exploited by the bacteria, in particular to assist their division. In conclusion, our work establishes TG2 as a key player in controlling glucose-derived metabolic pathways in mammalian cells, themselves hijacked by C. trachomatis to sustain their own metabolic needs.

Epithelial ovarian cancer represents the most lethal gynecological malignancy in the developed world, and can be divided into five main histological subtypes: high grade serous, endometrioid, clear cell, mucinous and low grade serous. These subtypes represent distinct disease entities, both clinically and at the molecular level. Molecular analysis has revealed significant genetic heterogeneity in ovarian cancer, particularly within the high grade serous subtype. As such, this subtype has been the focus of much research effort to date, revealing molecular subgroups at both the genomic and transcriptomic level that have clinical implications. However, stratification of ovarian cancer patients based on the underlying biology of their disease remains in its infancy. Here, we summarize the molecular changes that characterize the five main ovarian cancer subtypes, highlight potential opportunities for targeted therapeutic intervention and outline priorities for future research.

Transglutaminase 2 (TG2) is a ubiquitous enzyme with transamidating activity. We report here that the expression and activity of TG2 are enhanced in cells infected with the obligate intracellular bacteriaChlamydia trachomatis. Genetic or pharmacological inhibition of TG2 activity impair bacterial development. We show that TG2 increases glucose import by up-regulating the transcription of the glucose transporter genesGLUT-1andGLUT-3. Furthermore, TG2 activation drives one specific glucose-dependent pathway in the host, i.e. hexosamine biosynthesis. Mechanistically, we identify the glucosamine:fructose-6-phosphate amidotransferase (GFPT) among the substrates of TG2. GFPT modification by TG2 increases its enzymatic activity, resulting in higher levels of UDP-N-acetylglucosamine biosynthesis. As a consequence, TG2 activation results in increased proteinO-GlcNAcylation. The correlation between TG2 transamidating activity andO-GlcNAcylation is disrupted in infected cells because host hexosamine biosynthesis is being exploited by the bacteria, in particular to assist their division. In conclusion, our work establishes TG2 as a key player in controlling glucose-derived metabolic pathways in mammalian cells, themselves hijacked byC. trachomatisto sustain their own metabolic needs.

Background Disease relapse is the primary cause of death from ovarian carcinoma. Isolated lymph node relapse is a rare pattern of ovarian carcinoma recurrence, with a reported median postrelapse survival of 2.5 to 4 years. To date, investigations have not compared isolated lymph node relapse ovarian carcinoma directly to a matched extranodal relapse cohort or performed molecular characterization of cases that subsequently experience isolated lymph node relapse. Objective Here we seek to compare the clinical outcome, tumor-infiltrating lymphocyte burden, and frequency of known prognostic genomic events in isolated lymph node relapse ovarian carcinoma vs extranodal relapse ovarian carcinoma. Study Design Forty-nine isolated lymph node relapse ovarian carcinoma patients were identified and matched to 49 extranodal relapse cases using the Edinburgh Ovarian Cancer Database, from which the clinical data for identified patients were retrieved. Matching criteria were disease stage, histologic subtype and grade, extent of residual disease following surgical debulking, and age at diagnosis. Clinicopathologic factors and survival data were compared between the isolated lymph node relapse and extranodal relapse cohorts. Genomic characterization of tumor material from diagnosis was performed using panel-based high-throughput sequencing and tumor-infiltrating T cell burden was assessed using immunohistochemistry for CD3+ and CD8+ cells. Results Isolated lymph node relapse cases demonstrated significantly prolonged postrelapse survival and overall survival vs extranodal relapse upon multivariable analysis (HRmulti = 0.52 [0.33–0.84] and 0.51 [0.31–0.84]). Diagnostic specimens from high-grade serous ovarian carcinomas that subsequently displayed isolated lymph node relapse harbored significantly greater CD3+ and CD8+ cell infiltration compared to extranodal relapse cases (P = .001 and P = .009, Bonferroni-adjusted P = .003 and P = .019). Isolated lymph node relapse high-grade serous ovarian carcinoma cases did not show marked enrichment or depletion of cases with BRCA1/2 mutation or CCNE1 copy number gain when compared to their extranodal relapse counterparts (24.4% vs 19.4% and 18.2% vs 22.6%, P = .865 and P = .900). Conclusion Isolated lymph node relapse ovarian carcinoma represents a distinct clinical entity with favorable outcome compared to extranodal relapse. There was no clear enrichment or depletion of BRCA1/2 mutation or CCNE1 gain in the isolated lymph node relapse ovarian carcinoma cohort compared with extranodal relapse cases, suggesting that these known prognostic genomically defined subtypes of disease do not display markedly altered propensity for isolated lymph node relapse. Diagnostic tumor material from isolated lymph node relapse patients demonstrated greater CD3+ and CD8+ cell infiltration, indicating stronger tumor engagement by T cell populations, which may contribute to the more indolent disease course of isolated lymph node relapse.

Epithelial ovarian cancer represents the most lethal gynaecological malignancy in the developed world, and can be divided into five main histological subtypes: high grade serous, endometrioid, clear cell, mucinous and low grade serous. These subtypes represent distinct disease entities, both clinically and at the molecular level. Molecular analysis has revealed significant genetic heterogeneity in ovarian cancer, particularly within the high grade serous subtype. As such, this subtype has been the focus of much research effort to date, revealing molecular subgroups at both the genomic and transcriptomic level that have clinical implications. However, stratification of ovarian cancer patients based on the underlying biology of their disease remains in its infancy. Here, we summarise the molecular changes that characterise the five main ovarian cancer subtypes, highlight potential opportunities for targeted therapeutic intervention and outline priorities for future research.

Endometrioid ovarian carcinomas (EnOCs) account for 10% of OC diagnoses, representing distinct biological and clinical entities compared to other OC subtypes. We recently reported two molecular subgrouping studies using >100 WT1-negative EnOCs: the first identified molecular subgroups of disease by unsupervised analysis of hormone receptor expression patterns, reporting favorable disease-specific survival (DSS) in the PR-high subgroups (PR+/ER+, PR+/ER- vs PR-/ER+, PR-/ER-). The latter study performed whole exome sequencing, identifying genomic events associated with differential DSS, including TP53 mutation (TP53m) and CTNNB1m. Here, we perform integrated analysis of these data to investigate the overlap between these molecular subgrouping layers. The PR-high subgroups demonstrated low TP53m rate (5% vs 26%, P=0.035) and frequent CTNNB1m (75% vs 26%, P There was no significant difference in tumor mutational burden, microsatellite instability or tumor heterogeneity as defined by Mutant Allele Tumour Heterogeneity (MATH) score between the hormone-receptor-based subgroups. These groups also demonstrated no significant difference in mutation rate of mismatch repair protein-encoding genes. Multivariable analysis identified only FIGO stage at diagnosis (P=0.002), optimal surgical debulking (P=0.035) and hormone receptor subgroup (P=0.004) as independently associated with DSS. TP53m and CTNNB1m were not independently associated with DSS (P=0.187 and P=0.166), though CTNNB1m demonstrated a trend for association in a corresponding model for relapse-free survival (RFS) (HR=0.26, P=0.064). Within PR-high cases, specific genomic events were not associated with significantly differential survival. Conversely, TP53m was associated with inferior outcome specifically in PR-low cases (P=0.010 for RFS; P=0.066 for DSS). Collectively, these data represent the first depiction of the overlay and interplay between recently identified EnOC subgroups defined by WES and hormone receptor expression patterns. They demonstrate that PR-high cases frequently harbor CTNNB1m, while TP53m is rare in this context. Moreover, they suggest that PR-high cases experience favorable outcome irrespective of genomic profile, while TP53m represents an important marker of prognosis in PR-low EnOC. Moreover, given the high expression of ER and PR in the CTNNB1m population, assessment of the potential efficacy of endocrine therapy in this population may now warrant investigation. Citation Format: Robert L. Hollis, John Thomson, Barbara Stanley, Alison M. Meynert, Michael Churchman, Tzyvia Rye, C. Simon Herrington, Charlie Gourley. Integrated analysis of whole exome sequencing and hormone receptor expression data in endometrioid ovarian cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4161.

Objectives. The role of endocrine therapy (ET) in high grade serous ovarian carcinoma (HGSOC) is poorly defined due to the lack of phase III data and significant heterogeneity of clinical trials performed. In this study, we sought to identify predictive factors of endocrine sensitivity in HGSOC. Methods. HGSOC patients who received at least four weeks of ET for relapsed disease following one line of chemotherapy at the Edinburgh Cancer Centre were identified. Exclusion criteria were use of endocrine therapy as maintenance therapy or of unknown duration. Duration of therapy and best CA125 response as per modified GCIG criteria were recorded. Oestrogen receptor (ER) histoscore, treatment free interval, prior lines of chemotherapy, and type of ET were evaluated as predictive factors. Results. Of 431 patients identified, 269 were eligible (77.0 % letrozole, 18.6% tamoxifen, 2.2% megesterol acetate, 2.2% other). The median duration of therapy was 126 days (range 28-1427 days). 32.7% remained on ET for ≥180 days and 14.1% for ≥365 days. The CA125 response and clinical benefit rates (response or stable disease) were 8.1% and 40.1% respectively. ER histoscore >200 (P=0.0016) and a treatment free interval of ≥180 days (P200 and a treatment free interval of ≥180 days are most likely to derive benefit.

Background Approximately half of high‐grade serous ovarian carcinomas (HGSOCs) demonstrate homologous recombination repair (HR) pathway defects, resulting in a distinct clinical phenotype comprising hypersensitivity to platinum, superior clinical outcome, and greater sensitivity to poly(adenosine diphosphate‐ribose) polymerase (PARP) inhibitors. EMSY, which is known to be amplified in breast and ovarian cancers, encodes a protein reported to bind and inactivate BRCA2. Thus, EMSY overexpression may mimic BRCA2 mutation, resulting in HR deficiency. However, to our knowledge, the phenotypic consequences of EMSY overexpression in HGSOC patients has not been explored. Methods Here we investigate the impact of EMSY expression on clinical outcome and sensitivity to platinum‐based chemotherapy using available data from transcriptomically characterized HGSOC cohorts. Results High EMSY expression was associated with better clinical outcome in a cohort of 265 patients with HGSOC from Edinburgh (overall survival multivariable hazard ratio, 0.58 [95% CI, 0.38‐0.88; P = .011] and progression‐free survival multivariable hazard ratio, 0.62 [95% CI, 0.40‐0.96; P = .030]). Superior outcome also was demonstrated in the Medical Research Council ICON7 clinical trial and multiple publicly available data sets. Patients within the Edinburgh cohort who had high EMSY expression were found to demonstrate greater rates of complete response to multiple platinum‐containing chemotherapy regimens (radiological complete response rate of 44.4% vs 12.5% at second exposure; P = .035) and corresponding prolonged time to disease progression (median, 151.5 days vs 60.5 days after third platinum exposure; P = .004). Conclusions Patients with HGSOCs demonstrating high EMSY expression appear to experience prolonged survival and greater platinum sensitivity, reminiscent of BRCA‐mutant cases. These data are consistent with the notion that EMSY overexpression may render HGSOCs HR deficient., Patients with high‐grade serous ovarian carcinomas demonstrating high expression levels of EMSY appear to experience prolonged survival and hypersensitivity to multiple lines of platinum‐based chemotherapy. These data support the notion that overexpression of the gene product of EMSY, which is reported to bind and inactivate BRCA2, may mimic the phenotype conferred by BRCA mutation.

Background Approximately 10–15% of ovarian carcinomas (OC) are attributed to inherited susceptibility, the majority of which are due to mutations in BRCA1 or BRCA2 (BRCA1/2). These patients display superior clinical outcome, including enhanced sensitivity to platinum-based chemotherapy. Here, we seek to investigate whether BRCA1/2 status influences the response rate to single-agent pegylated liposomal doxorubicin (PLD) in high grade serous (HGS) OC. Methods One hundred and forty-eight patients treated with single-agent PLD were identified retrospectively from the Edinburgh Ovarian Cancer Database. DNA was extracted from formalin-fixed paraffin-embedded (FFPE) archival tumour material and sequenced using the Ion Ampliseq BRCA1 and BRCA2 panel. A minimum variant allele frequency threshold was applied to correct for sequencing artefacts associated with formalin fixation. Results A superior response rate to PLD was observed in patients with HGS OC who harboured variants likely to affect BRCA1 or BRCA2 function compared to the BRCA1/2 wild-type population (36%, 9 of 25 patients versus 12.1%, 7 of 58 patients; p = 0.016). An enhanced response rate was also seen in patients harbouring only the BRCA1 SNP rs1799950, predicted to be detrimental to BRCA1 function (50%, 3 of 6 patients versus 12.1%, 7 of 58 patients; p = 0.044). Conclusions These data demonstrate that HGS OC patients with BRCA1/2 variants predicted damaging to protein function experience superior sensitivity to PLD, consistent with impaired DNA repair. Further characterisation of rs1799950 is now warranted in relation to chemosensitivity and susceptibility to developing ovarian carcinoma. Electronic supplementary material The online version of this article (10.1186/s12885-017-3981-2) contains supplementary material, which is available to authorized users.

Approximately a fifth of ovarian carcinoma (OC) is associated with inherited germline mutations, most commonly in the DNA repair genes BRCA1 or BRCA2 (BRCA). BRCA1- and BRCA2-associated OCs have historically been described as a single subgroup of OC that displays a distinct set of characteristics termed the "BRCAness" phenotype. The hallmarks of this phenotype are superior clinical outcome and hypersensitivity to platinum-based chemotherapy and poly-(ADP-ribose) polymerase (PARP) inhibitors. However, growing evidence suggests that BRCA1- and BRCA2-associated OCs display distinct characteristics, most notably in long-term patient survival. Furthermore, recent data indicate that the site of BRCA1 mutation is important with regard to platinum and PARP inhibitor sensitivity. Here, we summarize the body of research describing the BRCAness phenotype and highlight the differential implications of different BRCA mutations with regard to clinicopathologic features, therapy sensitivity and clinical outcome in OC.

High grade serous ovarian carcinomas (HGSOCs) are molecularly and clinically heterogeneous malignancies. Currently, molecular stratification of patient care is limited to tumors rendered homologous recombination deficient (HRD) by BRCA1/2 mutation (BRCAm). Here we explore the overlap, interplay and clinical impact of molecular subgrouping layers in a cohort of 362 FFPE HGSOCs. We overlay genomic subgrouping and tumor-infiltrating lymphocyte (TIL) burden with the three transcriptionally-defined subtypes (Immune, Angio and AngioImmune) we have previously reported as associated with survival and bevacizumab sensitivity. The BRCAm group, the Immune subtype and those with high CD8+ TIL burden demonstrated prolonged overall survival (OS) as previously reported. The OS benefit of CD8+ TILs was abrogated in the context of gross residual disease following debulking [multivariable hazard ratio (mHR)=0.51 (0.34-0.78) vs 0.93 (0.76-1.52)]. BRCAwild-type patients demonstrating high expression of EMSY, encoding the BRCA2-binding protein EMSY, demonstrated prolonged OS [mHR=0.48 (0.29-0.79)]. BRCA2m and high-EMSY patients displayed greater chemosensitivity (first-line CA125-CR 94.4% and 81.3% vs 48.2%, P There was significant enrichment and depletion of BRCAm and CCNE1-gain (CCNE1g) in the Immune subtype (28.9% vs 6.3%, P=0.001 and 9.1% vs 17.4%, P=0.050). The Angio subtype harboured far fewer CD8+ TILs compared to the Immune and AngioImmune subtypes (P The clinical impact of CCNE1g was modulated by transcriptomic subtype: in the Immune group, CCNE1g was associated with poor OS [mHR=3.32 (1.49-7.41)], while in the Angio group CCNE1g cases had favourable outcome [PFS mHR=0.26 (0.10-0.68)]. CD8+ TIL burden was not associated with outcome in CCNE1g cases. Missense TP53 mutation was associated with better outcome versus TP53-null mutations in BRCAm patients [PFS mHR=0.43 (0.14-0.82)], but not in the context of HR proficiency [mHR=0.90 (0.67-1.22)]. Integrated classification using the consensus of favourable and unfavourable HR-centric (HRD favourable, HR-proficient unfavourable) and transcriptomic (Immune favourable, Angio/AngioImmune unfavourable) subgrouping yielded three groups with distinct OS [favourable vs unfavourable mHR=0.49 (0.34-0.74); favourable vs no-consensus mHR=0.64 (0.42-0.98); unfavourable vs no-consensus mHR=1.31 (1.00-1.70)]. Together, these data paint a more granular picture of the clinical impact of HGSOC subgroups and demonstrate novel candidate interactions between subgrouping layers. The poorest outcome groups represent those with most to gain from trials of novel treatment regimens. Citation Format: Robert L. Hollis, Alison M. Meynert, Michael Churchman, Tzyvia Rye, Patricia Roxburgh, Daniel Stetson, Athena Matakidou, Brian Dougherty, J. Carl Barrett, Ruth E. March, Colin A. Semple, C. Simon Herrington, Charlie Gourley. Multi-layer molecular characterization of high grade serous ovarian carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 749.

5553 Background: Endometrioid ovarian carcinomas (EC) have been historically under-investigated. We sought to determine the molecular landscape of contemporarily defined EC using whole exome sequencing (WES). Methods: Tumours diagnosed as EC between May 1980 and December 2013 were identified through the Edinburgh Ovarian Cancer Database. Pathology review was performed according to WHO 2014. Other pathologies including WT1 positive HGSOC were excluded. A selected cohort underwent WES and were analysed for single nucleotide and copy number variants across a panel of genes previously reported as mutated in endometrial, ovarian or pan cancer studies. Tissue microarrays were stained for ER, PR and AR. Multivariable analysis for disease specific survival (DSS) was performed. Results: 125 tumours were included. 61 tumours of all grades underwent WES. 5 molecular groups were identified based on the presence of TP53 mutations (45.9%); or an EClike profile (one or more mutations in ARID1A (41.0%); CTNNB1 (31.1%), PTEN (24.6%) or PIK3CA (23.0%)). Tumours with no mutations in EClike genes were termed ECnull. Each group demonstrated differential DSS (table). Some ECnull: TP53mut tumours also displayed mutations in KRAS, APC and mismatch repair genes. Unsupervised clustering analysis based on the top 100 differentially mutated genes across the dataset validated these groups. Somatic copy number alterations were significantly higher in the TP53mu t groups than the TP53wt groups (Plike genes in the ECnull groups. A PR histoscore of >150, but not ER or AR, was more frequent in the TP53wt group compared to the TP53mut groups (P=0.003). TP53mut status (P=0.0182) and PR histoscore ≤150 (P=0.0115) were independently associated with DSS. Conclusions: EC is a heterogeneous disease comprising 5 molecular subgroups each demonstrating differential clinical outcome. TP53 mutations and PR histoscore ≤150 are independently associated with poor prognosis. [Table: see text]

EMSY, encoding a BRCA2-binding protein, is reportedly amplified in 6-18% of high grade serous ovarian carcinomas (HGSOCs). As a negative regulator of BRCA2, HGSOCs with EMSY overexpression may mimic BRCA-mutant patients, who experience superior clinical outcome and hypersensitivity to platinum chemotherapy and PARP inhibition by virtue of homologous recombination deficiency (HRD). Here we investigate the impact of EMSY expression, extracted from local and publicly available transcriptomic data, on the outcome and platinum sensitivity of HGSOCs. Platinum response data were collected from the Edinburgh Ovarian Cancer Database. Overall survival (OS) and progression-free survival (PFS) differences were assessed using multivariate cox regression accounting for age, stage at diagnosis and debulking status. Within the Edinburgh cohort, high EMSY expression was associated with superior OS and PFS (table 1). Datasets from the MRC ICON7 trial control arm, Tothill et al, Mateescu et al, Pils et al, and TCGA cohorts demonstrated similar benefit for high-EMSY patients. Within the Edinburgh cohort, high-EMSY patients displayed significantly superior complete response (CR) rate to platinum at second (radio CR 44.4% vs 12.5%, P = 0.035; CA125 CR 88.0% vs 55.0%, P = 0.002) and third exposure (radio CR 50.0% vs 5.9%, P = 0.080; CA125 CR 53.3% vs 21.3%, P = 0.021), with prolonged time to progression (median 127 vs 83.5 days from second platinum, P = 0.084; median 151.5 vs 60.5 days from third platinum, P = 0.004). Within high-risk (advanced stage suboptimally debulked) HGSOCs, more high-EMSY patients remained recurrence-free 5 and 10 years from diagnosis (17.6% vs 2.7%, P = 0.031; 12.5% vs 0.9%, P = 0.041). Together these data demonstrate a subgroup of HGSOCs defined by high EMSY expression experience superior clinical outcome and platinum sensitivity, consistent with HRD. This subgroup may therefore represent HGSOCs that are also sensitive to PARP inhibition. DatasetEventMulti HR95% CIPEdinburghOS0.590.39 – 0.900.013PFS0.600.38 – 0.930.022MRC ICON7 control armOS0.210.07 – 0.680.009Tothill (primary tumour masses)OS0.280.09 – 0.900.032MateescuOS0.430.18 – 0.990.048PilsOS0.270.08 – 0.870.028TCGA advanced stage patientsPFS0.690.45 – 1.050.081 Citation Format: Robert L. Hollis, Michael Churchman, Tzyvia Rye, Andrena M. McCavigan, Laura A. Knight, Richard Kennedy, C. Simon Herrington, Charlie Gourley. High EMSY expression defines a BRCA-like subgroup of high-grade serous ovarian carcinoma with superior survival and platinum sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 322.