Homologous Recombination Repair Deficiency in Metastatic Prostate Cancer: New Therapeutic Opportunities.

More than 20% of metastatic prostate cancer carries genomic defects involving DNA damage repair pathways, mainly in homologous recombination repair-related genes. The recent approval of olaparib has paved the way to precision medicine for the treatment of metastatic prostate cancer with PARP inhibitors in this subset of patients, especially in the case of BRCA1 or BRCA2 pathogenic/likely pathogenic variants. In face of this new therapeutic opportunity, many issues remain unsolved. This narrative review aims to describe the relationship between homologous recombination repair deficiency and prostate cancer, the techniques used to determine homologous recombination repair status in prostate cancer, the crosstalk between homologous recombination repair and the androgen receptor pathway, the current evidence on PARP inhibitors activity in metastatic prostate cancer also in homologous recombination repair-proficient tumors, as well as emerging mechanisms of resistance to PARP inhibitors. The possibility of combination therapies including a PARP inhibitor is an attractive option, and more robust data are awaited from ongoing phase II and phase III trials outlined in this manuscript.

CDK inhibition results in pharmacologic BRCAness increasing sensitivity to olaparib in BRCA1-WT and olaparib resistant in Triple Negative Breast Cancer.

One in three Triple Negative Breast Cancer (TNBC) is Homologous Recombination Deficient (HRD) and susceptible to respond to PARP inhibitor (PARPi), however, resistance resulting from functional HR restoration is frequent. Thus, pharmacologic approaches that induce HRD are of interest. We investigated the effectiveness of CDK-inhibition to induce HRD and increase PARPi sensitivity of TNBC cell lines and PDX models. Two CDK-inhibitors (CDKi), the broad range dinaciclib and the CDK12-specific SR-4835, strongly reduced the expression of key HR genes and impaired HR functionality, as illustrated by BRCA1 and RAD51 nuclear foci obliteration. Consequently, both CDKis showed synergism with olaparib, as well as with cisplatin and gemcitabine, in a range of TNBC cell lines and particularly in olaparib-resistant models. In vivo assays on PDX validated the efficacy of dinaciclib which increased the sensitivity to olaparib of 5/6 models, including two olaparib-resistant and one BRCA1-WT model. However, no olaparib response improvement was observed in vivo with SR-4835. These data support that the implementation of CDK-inhibitors could be effective to sensitize TNBC to olaparib as well as possibly to cisplatin or gemcitabine.

Development and Characterisation of a New Patient-Derived Xenograft Model of AR-Negative Metastatic Castration-Resistant Prostate Cancer.

As the treatment landscape for prostate cancer gradually evolves, the frequency of treatment-induced neuroendocrine prostate cancer (NEPC) and double-negative prostate cancer (DNPC) that is deficient for androgen receptor (AR) and neuroendocrine (NE) markers has increased. These prostate cancer subtypes are typically refractory to AR-directed therapies and exhibit poor clinical outcomes. Only a small range of NEPC/DNPC models exist, limiting our molecular understanding of this disease and hindering our ability to perform preclinical trials exploring novel therapies to treat NEPC/DNPC that are urgently needed in the clinic. Here, we report the development of the CU-PC01 PDX model that represents AR-negative mCRPC with PTEN/RB/PSMA loss and CTNN1B/TP53/BRCA2 genetic variants. The CU-PC01 model lacks classic NE markers, with only focal and/or weak expression of chromogranin A, INSM1 and CD56. Collectively, these findings are most consistent with a DNPC phenotype. Ex vivo and in vivo preclinical studies revealed that CU-PC01 PDX tumours are resistant to mCRPC standard-of-care treatments enzalutamide and docetaxel, mirroring the donor patient's treatment response. Furthermore, short-term CU-PC01 tumour explant cultures indicate this model is initially sensitive to PARP inhibition with olaparib. Thus, the CU-PC01 PDX model provides a valuable opportunity to study AR-negative mCRPC biology and to discover new treatment avenues for this hard-to-treat disease.

First-line combination treatment with PARP and androgen receptor-signaling inhibitors in HRR-deficient mCRPC: Applying clinical study findings to clinical practice in the United States.

INTRODUCTION: Metastatic castration-resistant prostate cancer (mCRPC) remains incurable and develops from biochemically recurrent PC treated with androgen deprivation therapy (ADT) following definitive therapy for localized PC, or from metastatic castration-sensitive PC (mCSPC). In the mCSPC setting, treatment intensification of ADT plus androgen receptor (AR)-signaling inhibitors (ARSIs), with or without chemotherapy, improves outcomes vs ADT alone. Despite multiple phase 3 trials demonstrating a survival benefit of treatment intensification in PC, there remains high use of ADT monotherapy in real-world clinical practice. Prior studies indicate that co-inhibition of AR and poly(ADP-ribose) polymerase (PARP) may result in enhanced benefit in treating tumors regardless of alterations in DNA damage response genes involved either directly or indirectly in homologous recombination repair (HRR). Three recent phase 3 studies evaluated the combination of a PARP inhibitor (PARPi) with an ARSI as first-line treatment for mCRPC: TALAPRO-2, talazoparib plus enzalutamide; PROpel, olaparib plus abiraterone acetate and prednisone (AAP); and MAGNITUDE, niraparib plus AAP. Results from these studies have led to the recent approval in the United States of talazoparib plus enzalutamide for the treatment of mCRPC with any HRR alteration, and of both olaparib and niraparib indicated in combination with AAP for the treatment of mCRPC with BRCA alterations. SUMMARY: Here, we review the newly approved PARPi plus ARSI treatments within the context of the mCRPC treatment landscape, provide an overview of practical considerations for the combinations in clinical practice, highlight the importance of HRR testing, and discuss the benefits of treatment intensification for patients with mCRPC.

Evaluating homologous recombination activity in tissues to predict the risk of hereditary breast and ovarian cancer and olaparib sensitivity.

Homologous recombination (HR) repairs DNA damage including DNA double-stranded breaks and alterations in HR-related genes results in HR deficiency. Germline alteration of HR-related genes, such as BRCA1 and BRCA2, causes hereditary breast and ovarian cancer (HBOC). Cancer cells with HR deficiency are sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors and DNA-damaging agents. Thus, accurately evaluating HR activity is useful for diagnosing HBOC and predicting the therapeutic effects of anti-cancer agents. Previously, we developed an assay for site-specific HR activity (ASHRA) that can quantitatively evaluate HR activity and detect moderate HR deficiency. HR activity in cells measured by ASHRA correlates with sensitivity to the PARP inhibitor, olaparib. In this study, we applied ASHRA to lymphoblastoid cells and xenograft tumor tissues, which simulate peripheral blood lymphocytes and tumor tissues, respectively, as clinically available samples. We showed that ASHRA could be used to detect HR deficiency in lymphoblastoid cells derived from a BRCA1 pathogenic variant carrier. Furthermore, ASHRA could quantitatively measure the HR activity in xenograft tumor tissues with HR activity that was gradually suppressed by inducible BRCA1 knockdown. The HR activity of xenograft tumor tissues quantitatively correlated with the effect of olaparib. Our data suggest that ASHRA could be a useful assay for diagnosing HBOC and predicting the efficacy of PARP inhibitors.

Olaparib not cost-effective as maintenance therapy for platinum-sensitive, BRCA1/2 germline-mutated metastatic pancreatic cancer.

OBJECTIVE: To assess the cost-effectiveness and budget impact of olaparib as a maintenance therapy in platinum-responsive, metastatic pancreatic cancer patients harboring a germline BRCA1/2 mutation, using the Swiss context as a model. METHODS: Based on data from the POLO trial, published literature and local cost data, we developed a partitioned survival model of olaparib maintenance including full costs for BRCA1/2 germline testing compared to FOLFIRI maintenance chemotherapy and watch-and-wait. We calculated the incremental cost-effectiveness ratio (ICER) for the base case and several scenario analyses and estimated 5-year budget impact. RESULTS: Comparing olaparib with watch-and wait and maintenance chemotherapy resulted in incremental cost-effectiveness ratios of CHF 2,711,716 and CHF 2,217,083 per QALY gained, respectively. The 5-year costs for the olaparib strategy in Switzerland would be CHF 22.4 million, of which CHF 11.4 million would be accounted for by germline BRCA1/2 screening of the potentially eligible population. This would amount to a budget impact of CHF 15.4 million (USD 16.9 million) versus watch-and-wait. CONCLUSIONS: Olaparib is not a cost-effective maintenance treatment option. Companion diagnostics are an equally important cost driver as the drug itself.

CRABP2 reduces the sensitivity of Olaparib in ovarian cancer by downregulating Caspase-8 and decreasing the production of reactive oxygen species.

Poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors, such as Olaparib, have been pivotal in treating BRCA-deficient ovarian cancer. However, their efficacy is limited in over 40% of BRCA-deficient patients, with acquired resistance posing new clinical challenges. To address this, we employed bioinformatics methods to identify key genes impacting Olaparib sensitivity in ovarian cancer. Through comprehensive analysis of public databases including GEO, CPTAC, Kaplan Meier Plotter, and CCLE, we identified CRABP2 as significantly upregulated at both mRNA and protein levels in ovarian cancer, correlating with poor prognosis and decreased Olaparib sensitivity. Using colony formation and CCK-8 assays, we confirmed that CRABP2 knockdown in OVCAR3 and TOV112D cells enhanced sensitivity to Olaparib. Additionally, 4D label-free quantitative proteomics analysis, GSEA, and GO/KEGG analysis revealed CRABP2's involvement in regulating oxidation signals. Flow cytometry, colony formation assays, and western blotting demonstrated that CRABP2 knockdown promoted ROS production by activating Caspase-8, thereby augmenting Olaparib sensitivity and inhibiting ovarian cancer cell proliferation. Moreover, in xenograft models, CRABP2 knockdown significantly suppressed tumorigenesis and enhanced Olaparib sensitivity, with the effect being reversed upon Caspase-8 knockdown. These findings suggest that CRABP2 may modulate Olaparib sensitivity in ovarian cancer through the Caspase-8/ROS axis, highlighting its potential as a target for Olaparib sensitization.

FSP1 inhibition enhances olaparib sensitivity in BRCA-proficient ovarian cancer patients via a nonferroptosis mechanism.

Poly ADP-ribose polymerase inhibitors (PARPis) exhibit promising efficacy in patients with BRCA mutations or homologous repair deficiency (HRD) in ovarian cancer (OC). However, less than 40% of patients have HRD, it is vital to expand the indications for PARPis in BRCA-proficient patients. Ferroptosis suppressor protein 1 (FSP1) is a key protein in a newly identified ferroptosis-protective mechanism that occurs in parallel with the GPX4-mediated pathway and is associated with chemoresistance in several cancers. Herein, FSP1 is reported to be negatively correlated with the prognosis in OC patients. Combination therapy comprising olaparib and iFSP1 (a FSP1 inhibitor) strongly inhibited tumour proliferation in BRCA-proficient OC cell lines, patient-derived organoids (PDOs) and xenograft mouse models. Surprisingly, the synergistic killing effect could not be reversed by ferroptosis inhibitors, indicating that mechanisms other than ferroptosis were responsible for the synergistic lethality. In addition, cotreatment was shown to induce increased γH2A.X foci and to impair nonhomologous end joining (NHEJ) activity to a greater extent than did any single drug. Mass spectrometry and immunoprecipitation analyses revealed that FSP1 interacted with Ku70, a classical component recruited to and occupying the end of double-strand breaks (DSBs) in the NHEJ process. FSP1 inhibition decreased Ku70 PARylation, impaired subsequent DNA-PKcs recruitment to the Ku complex at DSB sites and was rescued by restoring PARylation. These findings unprecedentedly reveal a novel role of FSP1 in DNA damage repair and provide new insights into how to sensitize OC patients to PARPi treatment.

Olaparib for the Treatment of Patients With Metastatic Castration-Resistant Prostate Cancer and Alterations in BRCA1 and/or BRCA2 in the PROfound Trial.

Olaparib improved PFS and OS across subgroups of BRCA1/2mut #prostatecancer patients in the PROFOUND phase III trial.

Clinical characterization of patients with gBRCA1/2 mutation-positive unresectable pancreatic cancer: a multicenter prospective study.

BACKGROUND: Accumulating evidence has demonstrated platinum-based chemotherapy followed by maintenance therapy with a poly Adenosine diphosphate (ADP)-ribose polymerase inhibitor (olaparib) show benefits in unresectable pancreatic cancer with a germline (g)BRCA1/2 mutation. Evaluation of the germline BRCA1 and BRCA2 mutation is essential for making decisions on a treatment strategy for patients with unresectable pancreatic cancer. However, the detection rates of germline BRCA1 and BRCA2 mutations and efficacy of maintenance with olaparib remain undetermined, prospectively, in Japan. METHODS & RESULTS: In this prospective analysis, the rate of germline BRCA1 and BRCA2 mutations and efficacy of chemotherapy were analyzed in 136 patients with pancreatic cancer who underwent BRACAnalysis® (85 patients) or FoundationOne® CDx (51 patients) between January 2020 and July 2022. A total of six patients (4.4%) had a germline BRCA1 and BRCA2 mutation. Five patients were treated with modified FOLFIRINOX and one with fluorouracil and oxaliplatin. All patients continued platinum-based chemotherapy for ˃4 months and were subsequently treated with olaparib as a maintenance therapy. The response rate to platinum-based chemotherapy in the germline BRCA1 and BRCA2 mutation-positive group was significantly better than that of the germline BRCA1 and BRCA2 mutation-negative group (66% vs 23%, P = 0.04). All patients harbouring a germline BRCA1 and BRCA2 mutation were able to switch to olaparib. The median progression-free survival using olaparib was 5.7 months (range 3.0-9.2). CONCLUSIONS: The rate of germline BRCA1 and BRCA2 mutations found in patients with unresectable pancreatic cancer was comparable to those of previous studies.An analysis of germline BRCA1 and BRCA2 mutations has benefits for all patients with unresectable pancreatic cancer with regard to decisions on therapeutic strategies in a clinical practice setting.

Design and synthesis of the first PARP-1 and proteasome dual inhibitors to treat breast cancer.

PARP-1 is a crucial factor in repairing DNA single strand damage and maintaining genomic stability. However, the use of PARP-1 inhibitors is limited to combination with chemotherapy or radiotherapy, or as a single agent for indications carrying HRR defects. The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal manner by which cells regulate protein homeostasis. Proteasome inhibitors can cooperate with PARP-1 inhibitors to inhibit DNA homologous recombination repair function. In this study, we designed and synthesized the first dual PARP-1 and proteasome inhibitor based on Olaparib and Ixazomib. Both compounds 42d and 42i exhibited excellent proliferation inhibition and dual-target synergistic effects on cells that were insensitive to PARP-1 inhibitors. Further mechanistic evaluations revealed that 42d and 42i could inhibit homologous recombination repair function by down-regulating the expression of BRCA1 and RAD51. Additionally, 42i induced more significant apoptosis and showed better inhibitory effect on cell proliferation in clonal formation experiments in breast cancer cells than 42d. In summary, our study presented a new class of dual PARP-1/proteasome inhibitors with significant synergistic effects for the treatment of breast cancer.

Cytological Study of Topical Effect of Azelastine Hydrochloride on the Nasal Mucous Membrane Cells in Various Nasal Rhinitis Types.

Previous reports on the benefits of using local therapy with azelastine in rhinitis focus on the assessment of clinical symptoms and the analysis of nasal lavage for the presence of inflammatory cells and the expression of adhesion molecules. Little attention has been paid to studies assessing the effect of azelastine on individual cytotypes of the nasal mucosa, especially epithelial cells, also in the context of inducing morphological changes. The aim of this study was the cytological analysis of swabs taken from the surface of the nasal mucosa of patients with allergic rhinitis (AR) and nonallergic/vasomotor rhinitis (NAR/VMR) who were subjected to 4 weeks of therapy with azelastine and then comparing the obtained results with the pre-treatment condition. The technique of obtaining materials for cytoanalysis included sampling, staining of smears, microscopic analysis, and preparation of cytograms. Our studies confirmed the therapeutic benefits of azelastine in both study groups. Significant changes were demonstrated, confirming the regeneration of ciliated cells and the induction of autophagy and apoptosis in epithelial cells. Such changes indicate new mechanisms of action of azelastine, which play a significant role in restoring homeostasis in the nasal mucosa. The presented research also results in a detailed description of cytological changes in both studied rhinitis types, which complements the knowledge regarding prognostic indicators.

Targeted inhibition of the ATR/CHK1 pathway overcomes resistance to olaparib and dysregulates DNA damage response protein expression in BRCA2MUT ovarian cancer cells.

Olaparib is a PARP inhibitor (PARPi) approved for targeted treatment of ovarian cancer (OC). However, its efficacy is impeded by the inevitable occurrence of resistance. Here, we investigated whether the cytotoxic activity of olaparib could be synergistically enhanced in olaparib-resistant OC cells with BRCA2 reversion mutation by the addition of inhibitors of the ATR/CHK1 pathway. Moreover, we provide insights into alterations in the DNA damage response (DDR) pathway induced by combination treatments. Antitumor activity of olaparib alone or combined with an ATR inhibitor (ATRi, ceralasertib) or CHK1 inhibitor (CHK1i, MK-8776) was evaluated in OC cell lines sensitive (PEO1, PEO4) and resistant (PEO1-OR) to olaparib. Antibody microarrays were used to explore changes in expression of 27 DDR-related proteins. Olaparib in combination with ATR/CHK1 inhibitors synergistically induced a decrease in viability and clonogenic survival and an increase in apoptosis mediated by caspase-3/7 in all OC cells. Combination treatments induced cumulative alterations in expression of DDR-related proteins mediating distinct DNA repair pathways and cell cycle control. In the presence of ATRi and CHK1i, olaparib-induced upregulation of proteins determining cell fate after DNA damage (PARP1, CHK1, c-Abl, Ku70, Ku80, MDM2, and p21) was abrogated in PEO1-OR cells. Overall, the addition of ATRi or CHK1i to olaparib effectively overcomes resistance to PARPi exerting anti-proliferative effect in BRCA2MUT olaparib-resistant OC cells and alters expression of DDR-related proteins. These new molecular insights into cellular response to olaparib combined with ATR/CHK1 inhibitors might help improve targeted therapies for olaparib-resistant OC.

PARP Inhibitor Sensitizes BRCA-mutant Pancreatic Cancer to Oxaliplatin by Suppressing the CDK1/BRCA1 Axis.

BACKGROUND/AIM: Currently, olaparib, a poly(ADP-ribose) polymerase (PARP) inhibitor, has been approved as maintenance therapy for patients with germline BRCA mutations and metastatic pancreatic cancer. However, platinum-based chemotherapy, which induces synthetic lethality with PARP inhibitor treatment, is still controversial. Hence, we aimed to examine a platinum-based drug in combination with a PARP inhibitor and generate data regarding the use of a PARP inhibitor in the overall treatment of pancreatic cancer. MATERIALS AND METHODS: Using the Capan-1 cell line (BRCA2-mutant pancreatic cancer cell line), we evaluated the combinatorial effects of olaparib, a PARP inhibitor, and oxaliplatin by cell viability, combination index, western blotting, immunocytochemistry, flow cytometry, apoptosis assays and in vivo experiments. RESULTS: Capan-1 cells showed high sensitivity to olaparib due to the alteration in PARP activity, which led to cell death through the accumulation of oxaliplatin-induced DNA damage. Beyond DNA damage, oxaliplatin also suppressed the CDK1/BRCA1 signaling axis, which induced defects in homologous recombination repair. Additionally, inhibition of CDK1, a biomarker for oxaliplatin efficacy, induced cell death regardless of the BRCA mutation profile. CONCLUSION: Oxaliplatin may be used in combination with olaparib in PDAC patients with DNA damage repair mutations. Our findings highlight CDK1 as a potential therapeutic target for pancreatic cancer.

Deciphering the Pathways to PARP Sensitivity in Pancreatic Cancer.

A recent article analyzed paired cell-free DNA among patients with platinum-sensitive BRCA- or PALB2-mutated pancreatic cancer who received maintenance olaparib. Reversion mutations were linked with worse outcomes. These types of paired correlative studies are needed to improve our understanding of drug resistance and guide future clinical trials. See related article by Brown et al., p. 5207.

Pharmacological depletion of RNA splicing factor RBM39 by indisulam synergizes with PARP inhibitors in high-grade serous ovarian carcinoma.

Ovarian high-grade serous carcinoma (HGSC) is the most common subtype of ovarian cancer with limited therapeutic options and a poor prognosis. In recent years, poly-ADP ribose polymerase (PARP) inhibitors have demonstrated significant clinical benefits, especially in patients with BRCA1/2 mutations. However, acquired drug resistance and relapse is a major challenge. Indisulam (E7070) has been identified as a molecular glue that brings together splicing factor RBM39 and DCAF15 E3 ubiquitin ligase resulting in polyubiquitination, degradation, and subsequent RNA splicing defects. In this work, we demonstrate that the loss of RBM39 induces splicing defects in key DNA damage repair genes in ovarian cancer, leading to increased sensitivity to cisplatin and various PARP inhibitors. The addition of indisulam also improved olaparib response in mice bearing PARP inhibitor-resistant tumors. These findings demonstrate that combining RBM39 degraders and PARP inhibitors is a promising therapeutic approach to improve PARP inhibitor response in ovarian HGSC.

Validation of the Clinical Use of GIScar, an Academic-developed Genomic Instability Score Predicting Sensitivity to Maintenance Olaparib for Ovarian Cancer.

PURPOSE: The optimal application of maintenance PARP inhibitor therapy for ovarian cancer requires accessible, robust, and rapid testing of homologous recombination deficiency (HRD). However, in many countries, access to HRD testing is problematic and the failure rate is high. We developed an academic HRD test to support treatment decision-making. EXPERIMENTAL DESIGN: Genomic Instability Scar (GIScar) was developed through targeted sequencing of a 127-gene panel to determine HRD status. GIScar was trained from a noninterventional study with 250 prospectively collected ovarian tumor samples. GIScar was validated on 469 DNA tumor samples from the PAOLA-1 trial evaluating maintenance olaparib for newly diagnosed ovarian cancer, and its predictive value was compared with Myriad Genetics MyChoice (MGMC). RESULTS: GIScar showed significant correlation with MGMC HRD classification (kappa statistics: 0.780). From PAOLA-1 samples, more HRD-positive tumors were identified by GIScar (258) than MGMC (242), with a lower proportion of inconclusive results (1% vs. 9%, respectively). The HRs for progression-free survival (PFS) with olaparib versus placebo were 0.45 [95% confidence interval (CI), 0.33-0.62] in GIScar-identified HRD-positive BRCA-mutated tumors, 0.50 (95% CI, 0.31-0.80) in HRD-positive BRCA-wild-type tumors, and 1.02 (95% CI, 0.74-1.40) in HRD-negative tumors. Tumors identified as HRD positive by GIScar but HRD negative by MGMC had better PFS with olaparib (HR, 0.23; 95% CI, 0.07-0.72). CONCLUSIONS: GIScar is a valuable diagnostic tool, reliably detecting HRD and predicting sensitivity to olaparib for ovarian cancer. GIScar showed high analytic concordance with MGMC test and fewer inconclusive results. GIScar is easily implemented into diagnostic laboratories with a rapid turnaround.

Serum CA125 level as predictors of the efficacy of olaparib maintenance therapy for platinum-sensitive relapsed ovarian cancer.

AIM: Ovarian cancer is a gynecological malignancy with a poor prognosis. For platinum-sensitive relapsed ovarian cancer, maintenance therapy with poly-ADP ribose polymerase (PARP) inhibitors after chemotherapy is considered; however, olaparib treatment does not always lead to sufficient progression-free survival (PFS). This study aimed to identify factors that predict the efficacy of maintenance therapy using olaparib in platinum-sensitive relapsed ovarian cancer. METHODS: Twenty-seven patients with platinum-sensitive relapsed ovarian cancer, who received initial treatment and showed complete or partial response to prior chemotherapy at our hospital, were included. The primary outcome was the time from the end of previous platinum-based chemotherapy to disease progression (PFS). The Kaplan-Meier method was used to generate time-to-event curves for PFS; multivariate analysis was performed using the Cox proportional hazards regression model. RESULTS: The median PFS was 12 months (95% confidence interval [CI]: 8.3-15.8). Before olaparib administration, the median PFS was 12 months in the <4.1 neutrophil-to-lymphocyte ratio group and 4 months in the ≥4.1 group, with PFS being significantly better in the <4.1 group (log-rank: p = 0.023). When comparing serum cancer antigen 125 (CA125) levels, the median PFS was 13 months in the <18 U/mL group and 6 months in the >18 U/mL group (log-rank: p = 0.022). Multivariate Cox regression analysis revealed that CA125 was the factor affecting PFS (hazard ratio: 4.85; 95% CI: 1.53-15.38). CONCLUSIONS: Serum CA125 levels at olaparib initiation in patients with platinum-sensitive relapsed ovarian cancer may predict PFS as an effect of maintenance therapy using olaparib to treat recurrent disease.