POLAR Trial: Precision Immunotherapy Outcomes in Metastatic Pancreatic Cancer by HRD Status

A new clinical trial, dubbed POLAR, is offering a more nuanced understanding of how certain genetic mutations in pancreatic cancer respond to immunotherapy combinations. The study, published in JAMA Oncology, investigated the effectiveness of pembrolizumab and olaparib in patients with metastatic pancreatic cancer, categorizing them based on specific genetic alterations and their initial response to platinum-based chemotherapy. While the trial didn’t meet its primary endpoint across all groups, it revealed significant differences in response based on the type of genetic mutation present, and suggests a potential benefit for those with specific alterations in DNA repair genes.

Pancreatic cancer remains one of the most challenging cancers to treat, with a five-year survival rate of just 11% in the United States, according to the American Cancer Society. The POLAR trial aimed to identify which patients might benefit from combining an immunotherapy drug (pembrolizumab) with a PARP inhibitor (olaparib), a strategy showing promise in other cancers with DNA repair deficiencies.

Precision Immunotherapy: Defining the Cohorts

The POLAR trial took a precision medicine approach, dividing participants into three groups, or cohorts, based on their genetic profiles and how their cancer responded to initial chemotherapy. Cohort A included patients with mutations in core DNA repair genes – BRCA1, BRCA2, and PALB2 – who had stable disease for more than four months after platinum-based chemotherapy. Cohort B included patients with mutations in other DNA repair genes (ATM, CHEK2, and others) also with stable disease after chemotherapy. Finally, Cohort C included patients who had a good response to platinum chemotherapy for at least six months but didn’t have any of these specific DNA repair gene mutations. A total of 63 participants were enrolled between January 2021 and March 2024, across 42 institutions in nine countries, as detailed in PubMed.

Trial Design and Outcomes

All participants received a combination of olaparib (300mg twice daily) and pembrolizumab (800mg every three weeks, then every six weeks) until their disease progressed or the side effects became unacceptable. Researchers tracked several outcomes, including objective response rate (ORR – the percentage of patients whose tumors shrank significantly), progression-free survival (PFS – how long patients lived without their cancer getting worse), and overall survival (OS – how long patients lived overall). Tumor tissue and blood samples were collected at multiple timepoints to analyze genomic changes, immune responses, and other biomarkers.

The primary outcome measure was the confirmed objective response rate (ORR). While the trial did not meet its pre-specified co-primary endpoint of a 6-month PFS rate of 77%, the results showed varying degrees of response across the cohorts. The ORR in Cohort A (patients with BRCA1/2 or PALB2 mutations) was 35%, but did not reach statistical significance. Cohorts B and C had lower ORRs of 8% and 14%, respectively. However, a post-hoc analysis of Cohort A, including patients with profound radiographic responses to prior chemotherapy, increased the exploratory response rate to 52%.

Durable Responses and Genomic Insights

Notably, a significant number of patients in Cohort A experienced durable responses – meaning their cancer remained stable for an extended period. Thirteen of 33 patients in this cohort had ‘undefined’ disease at baseline due to prior chemotherapy responses, and 10 of those remained progression-free for more than four months, with eight experiencing progression-free survival exceeding 12 months. This suggests that patients with these specific genetic mutations and a history of responding to platinum chemotherapy may be particularly likely to benefit from the combination therapy.

Genomic analysis revealed that tumors in Cohort A (those with core HRD mutations) had a more immunogenic profile than those in Cohort C (those without HRD mutations). They exhibited a higher number of frameshift mutations, which are known to generate neoantigens – abnormal proteins that can trigger an immune response. This was accompanied by greater infiltration of immune cells, specifically T cells, into the tumors. The study found that participants with BRCA2 and PALB2 mutations demonstrated numerically similar PFS and OS, and longer than those with BRCA1 mutations.

Safety and Tolerability

The combination of pembrolizumab and olaparib was generally well-tolerated. No grade 4 or 5 treatment-related adverse events were reported. The most common grade 3 adverse events were anemia (15%) and abdominal infection (1.6%). Immune-related adverse events, such as colitis and pneumonitis, occurred in a small number of patients, but were generally manageable.

What Does This Indicate for Patients?

The POLAR trial highlights the importance of genomic testing in guiding treatment decisions for metastatic pancreatic cancer. Identifying patients with mutations in DNA repair genes, particularly BRCA1, BRCA2, and PALB2, may help clinicians select those most likely to benefit from immunotherapy combinations. However, it’s crucial to remember that this trial did not demonstrate a definitive benefit for all patients with these mutations. Further research is needed to confirm these findings and to identify other biomarkers that can predict response to therapy.

The study also underscores the complexity of the tumor microenvironment and the interplay between genomic alterations and immune responses. The observation that tumors with more immunogenic mutations and greater T cell infiltration tend to respond better to immunotherapy suggests that strategies to enhance the immune response may be particularly effective in these patients.

Looking Ahead: Ongoing Research and Future Directions

Researchers are continuing to analyze the data from the POLAR trial to explore the underlying mechanisms of response, and resistance. Additional analyses, including assessments of immune response endpoints and biomarker kinetics, are planned. The findings from this trial will inform the design of future clinical trials and may lead to the development of more personalized treatment strategies for metastatic pancreatic cancer. The study authors note that further investigation is needed to understand the role of ctDNA dynamics and the interplay between genomic features and immune infiltration in predicting response to therapy.

The evolving landscape of pancreatic cancer treatment emphasizes the need for ongoing surveillance and updates to clinical guidelines. Patients and healthcare providers should stay informed about the latest research findings and consult with specialists to determine the most appropriate treatment plan.