1 Introduction
Ovarian cancer remains the deadliest gynecologic malignant neoplasm worldwide, with 313 959 new diagnoses and 207 252 deaths globally in 2020 [
1]. In particular, 17.6% of these new diagnoses and 18.1% of these deaths occurred in China [
1]. For the past three decades, the first-line treatment for newly diagnosed advanced epithelial ovarian cancer is a combination of cytoreductive surgery and platinum-based chemotherapy. Although approximately 80% of patients attain complete clinical remission after receiving first-line treatment, approximately 70% of them experience a relapse within 3 years [
2]. Relapsed advanced ovarian cancer is considered incurable, emphasizing the importance of effective first-line treatments that can delay relapse and enhance the potential for achieving a cure.
Since 2018, the therapeutic landscape in the frontline setting has undergone a paradigm shift due to emerging evidence from six randomized phase III trials (SOLO-1, PAOLA-1, PRIMA, ATHENA-MONO, PRIME, and VELIA), that is, maintenance treatment with poly (ADP-ribose) polymerase (PARP) inhibitors is associated with a sustained progression-free survival (PFS) benefit [
3–
8]. On the basis of this compelling evidence, current ovarian cancer guidelines recommend maintenance therapy using PARP inhibitors, including olaparib, niraparib and rucaparib, to patients with newly diagnosed International Federation of Gynecology and Obstetrics (FIGO) stage III–IV epithelial ovarian cancer who have responded completely or partially to first-line platinum-based chemotherapy. The selection of the appropriate PARP inhibitor should be guided by genomic biomarkers [
2,
9,
10]. Olaparib was the first PARP inhibitor approved by the FDA for clinical use [
11]. For newly diagnosed ovarian cancer, olaparib has been approved for maintenance monotherapy in
BRCA mutation carriers in accordance with the findings from SOLO-1 [
8].
In August of 2018, the Chinese National Medical Products Administration (NMPA) approved olaparib for the maintenance treatment of platinum-sensitive recurrent ovarian cancer, making it the first PARP inhibitor available to patients in China. This approval was followed by NMPA’s endorsement of olaparib monotherapy as maintenance treatment for women newly diagnosed with BRCA1/2-mutated advanced-stage ovarian cancer in November 2019. In 2020, niraparib received NMPA approval as another maintenance therapy for newly diagnosed ovarian cancer, including patients without BRCA mutations. However, niraparib only became accessible as a first-line maintenance treatment for Chinese patients with BRCA wild-type ovarian cancer in 2022, following the acceptance of this indication by the National Healthcare Security Administration. Given that olaparib was the only option before 2022, clinicians in China prescribed it as the maintenance therapy to some newly diagnosed patients with BRCA wild-type tumors. These clinical practices provide us with an opportunity to investigate the efficacy and safety of olaparib in this specific patient population in the newly diagnosed setting.
2 Materials and methods
This retrospective cohort study used real-world data from 11 high-volume tertiary care centers in China (ClinicalTrials.gov identifier NCT05153603). The primary objective was to investigate the efficacy of olaparib maintenance therapy in patients without BRCA mutations by evaluating the 1-year PFS rate in the real world. This study was conducted in accordance with the principles stated in the Declaration of Helsinki, and the protocol was reviewed and approved by the institutional review board at each center. Although this research was funded by AstraZeneca, this company had no involvement in the study design, data collection methods, analysis, interpretation of the data, writing of the manuscript or decision to submit the article for publication to ensure the objectivity of this study. The retrospective nature of this work allowed for a waiver of the written informed consent.
Patients who were prescribed olaparib as the frontline maintenance therapy for newly diagnosed, histologically confirmed, advanced (FIGO stage III–IV) ovarian cancer, primary peritoneal cancer, and/or fallopian-tube cancer before April 2022 were identified. Only 18-year-old or older patients without evidence of BRCA1/2 deleterious or suspected deleterious mutations were included. All the selected patients were required to complete first-line platinum-based chemotherapy and achieve a complete response (CR) or partial response (PR) before receiving maintenance therapy. In addition, the patients were required to take at least one dose of olaparib tablets as monotherapy within 3 months of their last platinum-based chemotherapy cycle. The patients who had previously received any type of PARP inhibitor or concurrent anticancer therapy, including chemotherapy, immunotherapy, hormonal therapy (except hormone replacement therapy), radiotherapy, antiangiogenic agents such as bevacizumab and tyrosine kinase inhibitors, or biological therapy, during olaparib maintenance were excluded.
Data on patient demographics, tumor characteristics, treatments, adverse events during maintenance treatment, and outcomes were extracted from electronic medical records using a standardized data collection form. PFS was defined as the duration from the administration of first olaparib dose to the occurrence of disease progression (either radiologically or clinically) or death, whichever occurred first. Secondary endpoints included median PFS, median time from the administration of the first olaparib dose to the first subsequent therapy or death (TFST), and treatment-related adverse events (AEs). The latter were defined as events that occurred from the administration of the first olaparib dose until 28 days after the last dose and were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0 [
12]. Serious adverse events (SAEs) were defined as fatal or life-threatening events that require prolonged existing hospitalization, result in substantially disability or incapacity, or require medical or surgical intervention.
The sample size was determined based on precision considerations rather than statistical calculations. For the primary objective, a descriptive analysis was performed to estimate the 1-year PFS rate and its 95% confidence interval (CI) for mono-olaparib maintenance therapy. On the basis of the PFS for niraparib in PRIMA trial [
4], the 1-year PFS was assumed to be 54% in high-grade serous ovarian cancer patients with
BRCAwt tumors receiving first-line mono-olaparib maintenance therapy. According to estimation, 50 patients will provide a 95% CI of (39%, 68%) for 1-year PFS rate. This number was selected to ensure that the lower bound of the 95% CI for the 1-year PFS rate would not fall below 39%, which is higher than the 35% 1-year PFS rate reported for the PRIMA control group. PRIMA included patients with newly diagnosed FIGO III–IV stage ovarian high-grade serous or endometrioid tumors who achieved at least a PR after platinum-based chemotherapy [
4]. Given that the precision achieved was clinically acceptable, a sample size of 50 patients would be sufficient for estimating the 1-year PFS rate and its corresponding 95% CI in patients with
BRCA wild-type tumors receiving mono-olaparib maintenance therapy.
The demographic and baseline characteristics of the patients were described using descriptive statistics. Continuous variables were summarized as means with standard deviations, medians with ranges, and counts (n). Discrete variables were presented as counts and percentages (n (%)). Survival analysis was conducted using the Kaplan–Meier method. The Cox proportional hazards model was utilized to evaluate independent prognostic factors and estimate their effects on PFS. All variables with significance at P < 0.40 in univariate analysis were considered as candidates in the final model. This relatively liberal cutoff for the P value was selected due to the limited sample size, which may pose a risk of type II error when paired with a stringent cutoff. STATA 12.0 (Stata Press, College Station, TX, USA) was utilized for all statistical analyses. P < 0.05 was considered statistically significant.
3 Results
3.1 Patients
A total of 473 eligible cases were reviewed, and 50 patients were included in the final analysis as depicted in Fig.1 of the CONSORT diagram.
The patients received olaparib maintenance treatment between August 2018 and April 2022. All of them had high-grade serous histology, and the median age at diagnosis for the entire cohort was 54 years (range: 26 to 77). All the patients received homologous recombination deficiency (HRD) testing following debulking surgery, and HRD-positive tumors were identified in all cases. Tab.1 presents the patient characteristics. Among the 50 patients, 47 (94%) received platinum/paclitaxel as first-line chemotherapy regimen, and three (6%) received carboplatin in combination with liposomal doxorubicin.
Among the patients, 20% received neoadjuvant chemotherapy, four of whom (40%) received two courses, four (40%) received three courses, and the remaining two (20%) received four courses. Cytoreduction to minimal (≤ 1 cm) or no residual disease was achieved in 35 patients (70%). Following debulking surgery, the majority of the patients (84%) underwent six to eight cycles of chemotherapy, and 33 (66%) had CR to platinum-based chemotherapy. The median time from completion of the last chemotherapy cycle to the initiation of olaparib treatment was 6 weeks (range: 1 to 12).
3.2 Efficacy
Overall, 22 cases of recurrence and 2 deaths were recorded, and the median follow-up time was 16 months (range: 2 to 50). Fig.2 illustrates the PFS and overall survival (OS) curves. The 1-year PFS rate was 75.2% (95% CI, 63.4 to 89.2), and the 2-year PFS rate was 48.0% (95% CI, 28.7 to 65.0). The median PFS was 21.0 months (95% CI, 13.8 to 28.2, Fig.2). Median OS was not achieved (Fig.2).
Tab.2 summarizes the results of a Cox regression model of PFS fitted to the clinicopathologic variables of the patients. The extent of residual disease following debulking surgery and the response after first-line chemotherapy were identified as independent prognostic factors for PFS.
3.3 Post-recurrence treatment
Among the patients who experienced relapse, only 16 had data on post-recurrence treatments, and the median TFST was 12.5 months (95% CI, 6.0 to 28.0). Platinum-based chemotherapy was the first subsequent treatment in 14 out of 16 patients (87.5%), and two patients received repeated use of a PARP inhibitor (Fig.3).
3.4 Safety
During the maintenance treatment phase, all the patients received olaparib at an initial dosage of 300 mg twice daily. Eight (16%) patients required a dose adjustment, but none discontinued olaparib treatment due to AEs. Among the patients requiring dose adjustments, six did so because of toxic reactions, with anemia being the primary cause and affecting five out of these six patients. The remaining two patients modified their dosage due to economic constraints in affording the high-cost medication. Following the adjustment, seven patients were prescribed a total daily dose of 300 mg of olaparib, and one patient received a dose of 450 mg. Tab.3 summarizes olaparib-related AEs. No myelodysplastic syndrome or acute myeloid leukemia was recorded. Some patients experienced more than one AE, with a total of 11 AEs recorded. No patients experienced SAE, and the most severe AE was grade 3. The most common AEs of any grade were anemia (22%) and nausea (14%). The incidence of grade 3 AEs was 40%, with anemia being the most common.
4 Discussion
The 7-year follow-up data from the SOLO1 trial provide compelling evidence that 2 years of olaparib maintenance therapy significantly reduces the risk of death by 45% compared with the placebo [
13]. These robust findings emphasize the use of maintenance olaparib as an effective approach to achieve sustained remission in
BRCA mutation-carrying women diagnosed with advanced ovarian cancer, offering a potential avenue to increase the likelihood of a cure. Nonetheless, the effectiveness of olaparib as a mono-maintenance therapy for newly diagnosed ovarian cancer without
BRCA mutations remains uncertain. Conducting placebo-controlled trials in this context is challenging due to the established benefits of maintenance therapy with PARP inhibitors in the newly diagnosed setting [
3–
7]. Therefore, real-world data analysis represents the most feasible way to assess the efficacy of olaparib maintenance therapy in newly diagnosed ovarian cancer with
BRCA wild-type tumors. The results from this real-world multicenter study provide the first evidence that olaparib maintenance therapy is efficacious and well tolerated in patients with newly diagnosed HRD positive/
BRCA wild-type ovarian cancer and fills the data gap for olaparib.
PRIME evaluated the efficacy of maintenance therapy with PARP inhibitors in patients newly diagnosed with ovarian cancer in China [
14]. This trial enrolled 384 women who were randomly assigned to receive either niraparib or placebo. In the HRD-positive patients, niraparib maintenance therapy significantly improved the survival outcomes, with 1-year PFS rate of 73.9% and 2-year PFS rate of 52.0%. The HRD-positive cohort in PRIME included patients with somatic
BRCA mutations, and a higher number of patients achieved CR to platinum-based chemotherapy compared with that in the current study. Nevertheless, the 1-year and 2-year PFS rates in the current study were still comparable with those observed in PRIME. These findings provide strong evidence for the effectiveness of maintenance therapy with single-agent olaparib in patients with HRD-positive/
BRCA wild-type tumors. PRIMA also demonstrated the survival benefit of niraparib maintenance treatment in patients newly diagnosed with HRD-positive/
BRCA wild-type tumors [
4]; however, this study excluded patient with stage III disease who had no visible residual disease after primary debulking surgery.
The ATHENA–MONO study recently reported benefit for rucaparib maintenance across HRD subgroups [
6]. HRD-positive/
BRCA wild-type patients who were randomized to receive rucaparib had 1- and 2-year recurrence-free survival rates of 65.6% and 44.4%, respectively, with a median recurrence-free survival time of 20.3 months. These results are generally consistent with the present findings.
In the Cox proportional hazards model analysis, we found that the PFS benefit was most pronounced among patients with no residual disease following debulking surgery and those who achieved CR to frontline platinum-based chemotherapy. These findings align with previous reports [
15–
17] and highlight the importance of a dedicated multidisciplinary team of ovarian cancer management specialists who can provide the most sophisticated debulking surgery and standardized chemotherapy.
All the patients included in this study underwent HRD testing and tested positive. The exclusion of HRD-negative patients raises a question on the clinical decision-making of physicians. We postulate two potential reasons. First, existing evidence suggests that among patients with
BRCA wild-type ovarian cancer, HRD-positive individuals derive the greatest benefit from maintenance therapy with PARP inhibitors; meanwhile, the benefit for HRD-negative patients is extremely limited [
3,
5,
18,
19]. This phenomenon may have influenced physicians’ selection of patients for olaparib treatment. Second, the use of olaparib in patients with
BRCA wild-type tumors incurs high costs due to the lack of therapeutic indications and noninclusion in China’s National Reimbursement Drug List for this specific population. As a consequence, physicians tend to preferentially select HRD-positive patients to justify the costs. These individuals are more likely to benefit from olaparib therapy compared with those with HRD-negative tumors.
Owing to travel restrictions during the coronavirus pandemic in the past 3 years, patient follow-up was limited and collection of detailed information on every AE was challenging. Nonetheless, the toxicity profile observed in this study aligns with the expectations and previous findings, with anemia being the most frequently observed AE and the primary reason for dose adjustment [
8,
20–
22]. The incidence of grade 3 AEs was 40%, which is consistent with the 39% reported in the SOLO-1 trial [
3] but lower than the 56.8% incidence reported in the cohort of Chinese patients in SOLO-1 [
23]. A possible explanation is that the patients in SOLO-1 China cohort received more chemotherapy cycles compared with those in our study. We found no incidents of dose discontinuation, and only 15% of the patients required dose reduction, which is lower than the rates in previous RCTs [
3,
20,
24]. Basing on the data from community oncology practice, Eakin
et al. [
25] reported that 58% of patients receiving olaparib required dose reduction in the real-world setting. This discrepancy may be attributed to variations on how physicians manage PARP inhibitor toxicity reactions outside the controlled environment of clinical trials. The recommended schedule for olaparib dose modifications suggests reducing the dosage from 600 mg to 500 mg per day if a patient experiences grade 2 or higher AEs and further reducing to 400 mg per day when necessary [
26]. However, the limited accessibility of the 100 mg tablet for dose reduction in clinical practice in China has prompted clinicians to opt for reducing the dosage from 600 mg to 450 mg and then to 300 mg as demonstrated by our study. Considering the consistency of our patients’ survival outcomes with earlier studies and taking into account the findings of Francis
et al. who utilized data from SOLO-2 [
27], we believe that reducing the dosage of olaparib to manage associated AEs during the initial 12 weeks of treatment does not influence patient survival. During counseling regarding the need for dose reduction due to AEs, patients are reassured that their outcomes will not be compromised.
Several limitations to this study should be acknowledged. First, the retrospective design is subject to several limitations, including the possibility of incomplete data collection and provider selection bias. Second, although the PFS of our cohort was in line with that of previous studies [
6,
7], the follow-up period in the present study was relatively short and the median OS was not reached. Continuing the follow-up until OS results emerge is necessary. Third, the HRD assays employed in the present study have not been officially recognized as companion diagnostics for the use of PARP inhibitors. To date, no approved kit is available for HRD detection in China. Variations in HRD detection tests among our patients may result in disparities in accuracy [
28–
32]. Last but not the least, the small sample size and lack of control may have reduced the validity of the present study to a certain extent.
5 Conclusions
Our study presents the first evidence supporting the safety and efficacy of olaparib as mono-maintenance therapy for patients with newly diagnosed HRD-positive/BRCA wild-type ovarian cancer, addressing a previously unexplored area with significant clinical implications. The use of PARP inhibitors for maintenance therapy has become integral in the treatment of newly diagnosed ovarian cancer. Hence, our study fills an important gap by providing a viable treatment option for HRD positive/BRCA wild-type patients, particularly when other PARP inhibitors are unavailable or poorly tolerated. However, long follow-ups are required until OS results are achieved. The findings of this work will be validated in the ongoing phase III MONO-OLA1 study (NCT04884360).
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