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Ovarian cancer is an aggressive disease that is frequently detected at advanced stages and is initially very responsive to platinum-based chemotherapy. However, the majority of patients relapse following initial surgery and chemotherapy, highlighting the urgent need to develop new therapeutic strategies. In this Review, we outline the main therapeutic principles behind the management of newly diagnosed and recurrent epithelial ovarian cancer and discuss the current landscape of targeted and immune-based approaches.

Inhibitors of poly(ADP-ribose) polymerase (PARP) are considered one of the most active and exciting new therapies for the treatment of ovarian cancer. The anticancer activity of PARP inhibitors is based on the DNA repair vulnerability of many ovarian cancer cells, and multiple mechanisms of action of PARP inhibitors have been identified. As single agents, PARP inhibitors have demonstrated their greatest activity in ovarian cancer cells that harbor mutations in BRCA genes. Additionally, recent phase III studies have shown that single-agent PARP inhibitor activity extends beyond BRCA-related cancers and can benefit patients with ovarian cancers that do not have known BRCA mutations, especially when clinical characteristics such as platinum sensitivity and high-grade serous histology are present. PARP inhibitors have also been combined with chemotherapy, however, overlapping myelosuppression observed with PARP inhibitor and chemotherapy combinations has hampered development of these combinations. Contrariwise, PARP inhibitor and biologic agent combinations, specifically antiangiogenic agents, appear well tolerated and show promising activity in both BRCA mutated (BRCAm) and BRCA wild-type (BRCAwt) cancers. Currently, multiple clinical trials are underway examining the antitumor activity of PARP inhibitor combination therapy.

Late-line treatment options for patients with ovarian cancer are few, with the proportion of patients achieving an overall response typically less than 10%, and median overall survival after third-line therapy of 5–9 months. In this study (QUADRA), we investigated the activity of niraparib monotherapy as the fourth or later line of therapy. QUADRA was a multicentre, open-label, single-arm, phase 2 study that evaluated the safety and activity of niraparib in adult patients (≥18 years) with relapsed, high-grade serous (grade 2 or 3) epithelial ovarian, fallopian tube, or primary peritoneal cancer who had been treated with three or more previous chemotherapy regimens. The study was done in the USA and Canada, and 56 sites screened patients (50 sites treated at least one patient). Patients received oral niraparib 300 mg once daily continuously, beginning on day 1 and every cycle (28 days) thereafter until disease progression. The primary objective was the proportion of patients achieving an investigator-assessed confirmed overall response in patients with homologous recombination deficiency (HRD)-positive tumours (including patients with BRCA and without BRCA mutations) sensitive to their last platinum-based therapy who had received three or four previous anticancer therapy regimens (primary efficacy population). Efficacy analyses were additionally done in all dosed patients with measurable disease at baseline. Between April 1, 2015 and Nov 1, 2017, we screened 729 patients for eligibility and enrolled 463 patients, who were initiated on niraparib therapy. At the time of database lock (April 11, 2018), enrolment had closed and the study was ongoing, with 21 patients still on treatment. Patients had received a median of four (IQR 3–5) previous lines of therapy, and the median follow-up for overall survival was 12·2 months (IQR 3·7–22·1). 151 (33%) of 463 patients were resistant and 161 (35%) of 463 patients were refractory to the last administered platinum therapy. 13 (28%) of 47 patients in the primary efficacy population achieved an overall response according to RECIST (95% CI 15·6–42·6; one-sided p=0·00053). The most common drug-related grade 3 or worse treatment-emergent adverse events were anaemia (113 [24%] of 463 patients) and thrombocytopenia (95 [21%] of 463 patients). The most common treatment-emergent serious adverse events were small intestinal obstruction (34 [7%] of 463 patients), thrombocytopenia (34 [7%] of 463 patients), and vomiting (27 [6%] of 463 patients). One death due to gastric haemorrhage was considered treatment related. We observed clinically relevant activity of niraparib among women with heavily pretreated ovarian cancer, especially in patients with HRD-positive platinum-sensitive disease, which includes not only patients with a BRCA mutation but also a population with BRCA wild-type disease. We identified no new safety signals. Our data support expansion of the treatment indication for poly(ADP-ribose) polymerase inhibitors to include patients with HRD-positive ovarian cancer beyond those with BRCA mutations. Tesaro.

Malignant abdominal fluid (ascites) frequently develops in women with advanced high-grade serous ovarian cancer (HGSOC) and is associated with drug resistance and a poor prognosis 1 . To comprehensively characterize the HGSOC ascites ecosystem, we used single-cell RNA sequencing to profile ~11,000 cells from 22 ascites specimens from 11 patients with HGSOC. We found significant inter-patient variability in the composition and functional programs of ascites cells, including immunomodulatory fibroblast sub-populations and dichotomous macrophage populations. We found that the previously described immunoreactive and mesenchymal subtypes of HGSOC, which have prognostic implications, reflect the abundance of immune infiltrates and fibroblasts rather than distinct subsets of malignant cells 2 . Malignant cell variability was partly explained by heterogeneous copy number alteration patterns or expression of a stemness program. Malignant cells shared expression of inflammatory programs that were largely recapitulated in single-cell RNA sequencing of ~35,000 cells from additionally collected samples, including three ascites, two primary HGSOC tumors and three patient ascites-derived xenograft models. Inhibition of the JAK/STAT pathway, which was expressed in both malignant cells and cancer-associated fibroblasts, had potent anti-tumor activity in primary short-term cultures and patient-derived xenograft models. Our work contributes to resolving the HSGOC landscape 3 – 5 and provides a resource for the development of novel therapeutic approaches. Single-cell transcriptomics analysis of malignant ascites samples from patients with high-grade serous ovarian cancer reveals inter- and intra-patient heterogeneity in malignant cells, cancer-associated fibroblasts and macrophages.

PARP inhibitors (PARPi) have drastically changed the treatment landscape of advanced ovarian tumors with BRCA mutations. However, the impact of this class of inhibitors in patients with advanced BRCA -mutant breast cancer is relatively modest. Using a syngeneic genetically-engineered mouse model of breast tumor driven by Brca1 deficiency, we show that tumor-associated macrophages (TAMs) blunt PARPi efficacy both in vivo and in vitro. Mechanistically, BRCA1-deficient breast tumor cells induce pro-tumor polarization of TAMs, which in turn suppress PARPi-elicited DNA damage in tumor cells, leading to reduced production of dsDNA fragments and synthetic lethality, hence impairing STING-dependent anti-tumor immunity. STING agonists reprogram M2-like pro-tumor macrophages into an M1-like anti-tumor state in a macrophage STING-dependent manner. Systemic administration of a STING agonist breaches multiple layers of tumor cell-mediated suppression of immune cells, and synergizes with PARPi to suppress tumor growth. The therapeutic benefits of this combination require host STING and are mediated by a type I IFN response and CD8 + T cells, but do not rely on tumor cell-intrinsic STING. Our data illustrate the importance of targeting innate immune suppression to facilitate PARPi-mediated engagement of anti-tumor immunity in breast cancer. PARP inhibitor (PARPi) therapy has demonstrated only modest efficacy in advanced breast cancer with BRCA mutations. Here the authors show that, by suppressing PARPi-triggered DNA damage and reducing dsDNA production in BRCA1-deficient breast tumor cells, tumor associated macrophages contribute to PARPi resistance, that can be overcome by STING agonism.

In a placebo-controlled, phase 2 study, olaparib, an oral PARP inhibitor that should be effective in tumor cells with BRCA1/2 -related base excision repair defects, increased progression-free survival from 4 months to 8 months in patients with platinum-sensitive relapsed ovarian cancer. Ovarian cancer is the leading cause of death from gynecologic tumors in the Western world. 1 Approximately 80% of patients with newly diagnosed ovarian cancer have a response to platinum-based chemotherapy. However, most patients have relapses, and responses to subsequent therapies are generally short-lived. 2 – 6 Maintenance chemotherapy as part of first-line treatment has been shown to prolong control of ovarian cancer, 7 and disease control has also been prolonged with the combination of bevacizumab and chemotherapy in patients receiving first-line treatment 8 , 9 and in those with platinum-sensitive relapsed ovarian cancer. 10 However, new treatments are needed because most patients eventually have a relapse. . . .

The use of PARP inhibitors (PARPi) is growing widely as FDA approvals have shifted its use from the recurrence setting to the frontline setting. In parallel, the population developing PARPi resistance is increasing. Here we review the role of PARP, DNA damage repair, and synthetic lethality. We discuss mechanisms of resistance to PARP inhibition and how this informs on novel combinations to re-sensitize cancer cells to PARPi.

Olaparib is a poly(ADP-ribose) polymerase inhibitor and cediranib is an anti-angiogenic agent with activity against VEGF receptor (VEGFR) 1, VEGFR2, and VEGFR3. Both oral agents have antitumour activity in women with recurrent ovarian cancer, and their combination was active and had manageable toxicities in a phase 1 trial. We investigated whether this combination could improve progression-free survival (PFS) compared with olaparib monotherapy in women with recurrent platinum-sensitive ovarian cancer. In our randomised, open-label, phase 2 study, we recruited women (aged ≥18 years) who had measurable platinum-sensitive, relapsed, high-grade serous or endometrioid ovarian, fallopian tube, or primary peritoneal cancer, or those with deleterious germline BRCA1/2 mutations from nine participating US academic medical centres. We randomly allocated participants (1:1) according to permuted blocks, stratified by germline BRCA status and previous anti-angiogenic therapy, to receive olaparib capsules 400 mg twice daily or the combination at the recommended phase 2 dose of cediranib 30 mg daily and olaparib capsules 200 mg twice daily. The primary endpoint was progression-free survival analysed in the intention-to-treat population. The phase 2 trial is no longer accruing patients. An interim analysis was conducted in November, 2013, after 50% of expected events had occurred and efficacy results were unmasked. The primary analysis was performed on March 31, 2014, after 47 events (66% of those expected). The trial is registered with ClinicalTrials.gov, number NCT01116648. Between Oct 26, 2011, and June 3, 2013, we randomly allocated 46 women to receive olaparib alone and 44 to receive the combination of olaparib and cediranib. Median PFS was 17·7 months (95% CI 14·7–not reached) for the women treated with cediranib plus olaparib compared with 9·0 months (95% CI 5·7–16·5) for those treated with olaparib monotherapy (hazard ratio 0·42, 95% CI 0·23–0·76; p=0·005). Grade 3 and 4 adverse events were more common with combination therapy than with monotherapy, including fatigue (12 patients in the cediranib plus olaparib group vs five patients in the olaparib monotherapy group), diarrhoea (ten vs none), and hypertension (18 vs none). Cediranib plus olaparib seems to improve PFS in women with recurrent platinum-sensitive high-grade serous or endometrioid ovarian cancer, and warrants study in a phase 3 trial. The side-effect profile suggests such investigations should include assessments of quality of life and patient-reported outcomes to understand the effects of a continuing oral regimen with that of intermittent chemotherapy. American Recovery and Reinvestment Act grant from the National Institutes of Health (NIH) (3 U01 CA062490-16S2); Intramural Program of the Center for Cancer Research; and the Division of Cancer Treatment and Diagnosis, National Cancer Institute, NIH.

Necroptosis is a lytic programmed cell death mediated by the RIPK1-RIPK3-MLKL pathway. The loss of Receptor-interacting serine/threonine-protein kinase 3 (RIPK3) expression and necroptotic potential have been previously reported in several cancer cell lines; however, the extent of this loss across cancer types, as well as its mutational drivers, were unknown. Here, we show that RIPK3 expression loss occurs progressively during tumor growth both in patient tumor biopsies and tumor xenograft models. Using a cell-based necroptosis sensitivity screen of 941 cancer cell lines, we find that escape from necroptosis is prevalent across cancer types, with an incidence rate of 83%. Genome-wide bioinformatics analysis of this differential necroptosis sensitivity data in the context of differential gene expression and mutation data across the cell lines identified various factors that correlate with resistance to necroptosis and loss of RIPK3 expression, including oncogenes BRAF and AXL. Inhibition of these oncogenes can rescue the RIPK3 expression loss and regain of necroptosis sensitivity. This genome-wide analysis also identifies that the loss of RIPK3 expression is the primary factor correlating with escape from necroptosis. Thus, we conclude that necroptosis resistance of cancer cells is common and is oncogene driven, suggesting that escape from necroptosis could be a potential hallmark of cancer, similar to escape from apoptosis.

Ovarian cancer is not a single disease and can be subdivided into at least five different histological subtypes that have different identifiable risk factors, cells of origin, molecular compositions, clinical features and treatments. Ovarian cancer is a global problem, is typically diagnosed at a late stage and has no effective screening strategy. Standard treatments for newly diagnosed cancer consist of cytoreductive surgery and platinum-based chemotherapy. In recurrent cancer, chemotherapy, anti-angiogenic agents and poly(ADP-ribose) polymerase inhibitors are used, and immunological therapies are currently being tested. High-grade serous carcinoma (HGSC) is the most commonly diagnosed form of ovarian cancer and at diagnosis is typically very responsive to platinum-based chemotherapy. However, in addition to the other histologies, HGSCs frequently relapse and become increasingly resistant to chemotherapy. Consequently, understanding the mechanisms underlying platinum resistance and finding ways to overcome them are active areas of study in ovarian cancer. Substantial progress has been made in identifying genes that are associated with a high risk of ovarian cancer (such as BRCA1 and BRCA2 ), as well as a precursor lesion of HGSC called serous tubal intraepithelial carcinoma, which holds promise for identifying individuals at high risk of developing the disease and for developing prevention strategies. Ovarian cancer is a global health problem that is generally diagnosed at a late stage and has no effective screening strategy. This Primer by Matulonis et al . discusses the risk factors, genetics, diagnosis and management of ovarian cancer.