Did Olaparib and Tremelimumab Work in Recurrent Ovarian Cancer with BRCA Mutations?

In a phase I/II trial combining the PARP inhibitor olaparib with the CTLA-4 antibody tremelimumab in recurrent ovarian cancer with germline BRCA1/2 mutations, the response rate was 32,7%. However, the study did not meet its primary endpoint, median progression-free survival remained at 3,0 months, and adverse effects were frequent. Original article: Adams et al., Nature Communications (2026).

Why Does This Matter?

Ovarian cancer often responds well to initial treatment, but a substantial proportion of disease recurs, and, as the article emphasizes, cancer-related mortality remains high. In women carrying a germline BRCA mutation, PARP inhibitors have become a cornerstone of treatment; however, as their use increases, the number of patients with resistance to PARP inhibitors is also growing.

Although immune checkpoint inhibitors (immunotherapy) have provided long-term benefit in some cancers, such as melanoma, response rates in ovarian cancer are low. According to the article, response rates in PD-1/PD-L1 single-agent studies are approximately 15%. Researchers had reported that, in laboratory models of Brca1-deficient ovarian cancer, olaparib combined with CTLA-4 blockade produced long-term survival, whereas PD-1/PD-L1 blockade did not produce the same effect. This study is the first test of that hypothesis in humans.

Are Olaparib and Tremelimumab Effective Together in Ovarian Cancer?

No; the combination of olaparib and tremelimumab remains investigational. The phase I/II trial found a response rate of 32,7%, but the target response rate was not reached, and median progression-free survival remained at 3,0 months. Some patients achieved long-term control, but adverse effects were frequent and serious. It should therefore be evaluated only within a clinical trial.

How Was the Study Designed, and Who Took Part?

The study (NCT02571725) was a single-arm, open-label phase I/II trial conducted at five centers in the United States. Safety and dose were established in phase I; ORR was evaluated as the primary endpoint in phase II. The statistical design used a Simon two-stage model testing the hypothesis that the true response rate was 40% against 55%.

Why Was the Treatment Schedule Changed?

The protocol initially specified tremelimumab every 4 weeks for a total of 6 doses. At the data safety review in 2018, four of the first 14 patients had developed late-onset grade 3 immune-related toxicity during cycles 5 and 6. The protocol was therefore changed to 4 doses every 4 weeks, followed by administration every 12 weeks; the authors report that this change limited immune-related adverse effects in subsequent patients.

What Were the Study Results?

Under the prespecified criterion, benefit was required in 12 of the first 30 patients to pass the initial stage. Because this threshold was met, the study was expanded to 50 patients. However, the final analysis required at least 25 responses among 50 patients; the 16 responses fell well below this threshold. The authors also explicitly state that the study did not meet its primary efficacy endpoint.

A noteworthy finding is that responses could last a long time in individual patients: responses were confirmed by a second imaging assessment in ten patients, and four patients continued treatment despite imaging showing progression because their physicians identified benefit.

Were Results Different in Patients Previously Treated with a PARP Inhibitor?

60% of patients had used a PARP inhibitor before entering the study. Progression-free survival was markedly shorter in this subgroup: 2,6 months, compared with 8,0 months in patients without prior PARP inhibitor use (p<0,001). The difference in overall survival did not cross the statistical significance threshold (20,1 versus 27,5 months; p=0,053). Nevertheless, disease control was achieved in approximately one-quarter (24%) of patients previously treated with a PARP inhibitor. This was considered noteworthy in a group in which benefit from olaparib alone would not be expected; however, without a comparator arm, this study cannot determine whether the benefit of the combination was due to tremelimumab or to patient selection.

Conversely, disease progressed during olaparib and tremelimumab treatment in 21,1% of patients without prior PARP inhibitor use. This shows that BRCA status alone does not predict response and that additional biomarkers are needed for patient selection.

What Were the Most Common Adverse Effects During Treatment?

All patients experienced treatment-emergent adverse events. Hematological events, involving reduced blood counts, were attributed predominantly to olaparib, while most other events were attributed to tremelimumab as possibly or probably immune-related. Gastrointestinal findings were the most frequent category (95,9%), with grade 3 or higher events occurring in 32,7% of this category.

General warning signs of immune-related events are situations that a patient receiving treatment should report promptly to their oncology team:

• Diarrhea and abdominal pain: particularly bloody stools or an increase several times a day
• Fever and signs of infection: chills, cough and shortness of breath
• Extreme weakness: dizziness, low blood pressure and salt cravings
• Severe headache: when accompanied by visual changes, pituitary involvement should be considered
• Persistent nausea and vomiting: inability to take fluids and reduced urine output
• Excessive thirst and frequent urination: may indicate elevated blood sugar

What Are VSTM5 and IFIT1B, and Why Did They Stand Out?

The study performed RNA sequencing in 30 patients using archived tumor tissue obtained 15–154 months before the initial surgery. None of the established immunotherapy markers, including immune cell counts (CD4 and CD8 TIL), tumor mutational burden, PD-L1 expression and neoantigen burden, was associated with clinical benefit. By contrast, two genes stood out: IFIT1B, an interferon-response gene, and VSTM5, whose function is not yet fully understood.

The authors suggest that low IFIT expression may reflect tumors without chronic interferon signaling, which therefore remain susceptible to treatment-induced immune changes. This is a hypothesis. In an independent ovarian cancer dataset, TCGA with 299 patients, these two genes generally did not predict survival in untreated patients; a difference in progression-free survival was observed only for IFIT1B in a small BRCA-mutated subgroup of 16 patients. No association was found for VSTM5 in TCGA.

How Do These Results Compare with Other Immunotherapy Studies?

In the article's discussion, the authors compare their results with immune-based regimens in ovarian cancer. The graph below presents these figures as reported by the authors; the original studies were not separately accessed when preparing this article.

Current Evidence and Approval Status

The combined use of olaparib and tremelimumab has not received approval for ovarian cancer from any regulatory authority; the combination remains investigational. The drugs' independent approvals are as follows:

As a recent development in ovarian cancer immunotherapy, the article states that the PD-1 antibody pembrolizumab has received a new FDA approval with paclitaxel and bevacizumab for platinum-resistant disease. For annual summaries of approvals and advances, the AACR Cancer Progress Report can also be consulted.

Frequently Asked Questions

Are Olaparib and Tremelimumab Standard Treatment for Ovarian Cancer?

No. The combination has been tested only in a phase I/II trial; it is not standard treatment because the study did not meet its primary efficacy endpoint.

Why Was Tremelimumab Discontinued, and What Adverse Effects Occurred?

Tremelimumab was discontinued in 34,7% of patients because of immune-related adverse effects. Gastrointestinal findings, including diarrhea, colitis and nausea, were most common; hypophysitis and adrenal insufficiency were reported rarely.

Does the Combination Work in Patients Who Have Previously Used a PARP Inhibitor?

Progression-free survival was short in this group (2,6 months), although disease control was achieved in approximately one-quarter. The combination's benefit in these patients is uncertain and requires confirmation.

Can Patients Be Tested for VSTM5 or IFIT1B?

No; these markers were identified in an exploratory analysis of 30 patients and have not been independently validated. They are not used for treatment decisions.

Glossary

PARP inhibitor

A class of medicines that inhibit the PARP enzyme involved in DNA repair; olaparib belongs to this class and is particularly effective in tumors with BRCA mutations.

CTLA-4 (tremelimumab)

A checkpoint that limits T-cell activation; tremelimumab is an antibody that blocks this checkpoint.

Germline BRCA mutation

An alteration in the BRCA1 or BRCA2 gene that is present from birth and found in all cells.

Objective response rate (ORR)

The proportion of patients whose tumor size decreases beyond a specified threshold, achieving a complete or partial response.

Progression-free survival (PFS)

The time from starting treatment until disease progression or death.

Biomarker

A measurable indicator that may help predict response to treatment or the course of a disease.

Simon two-stage design

A phase II statistical design allowing a study to be stopped early if insufficient benefit is seen during the first stage.