A new Phase II clinical trial led by researchers at Memorial Sloan Kettering Cancer Center and Weill Cornell Medical College suggests that treating a subset of pancreatic cancer patients with a biomarker-guided maintenance strategy may result in a longer survival time. The study, published in Nature Medicine, emphasizes the growing potential of precision immunotherapy in one of the deadliest cancers.
The POLAR (Pembrolizumab and OLApaRib) trial focused on patients with metastatic pancreatic cancer whose tumors had homologous recombination deficiency (HRD), a genetic feature associated with impaired DNA repair. HRD is commonly caused by gene mutations in BRCA1, BRCA2, or PALB2, and it has been shown to increase sensitivity to platinum-based chemotherapy and PARP inhibitors, a class of drugs that further disrupt DNA repair.
In POLAR, 63 patients whose disease had stabilized following platinum chemotherapy were given a combination of the PARP inhibitor olaparib and the immune checkpoint inhibitor pembrolizumab as maintenance therapy. Participants were classified into three groups based on their tumor biology: those with core HRD mutations (cohort A), those with related but less well-defined mutations (cohort B), and those without HRD but with platinum-sensitive disease (cohort C).
Although the trial did not meet its primary endpoints, the results showed a significant clinical signal in the HRD group. Patients in cohort A had a median progression-free survival of 8.3 months and a median overall survival of 28 months, which is significantly longer than the average for advanced pancreatic cancer. Notably, 44% of these patients were still alive after three years, which is unusually high for this disease.
Response rates varied by genetic subgroup. Tumors with core HRD mutations had a 35% objective response rate, compared to only 8% and 14% in cohorts B and C, respectively. When patients who had previously achieved deep responses to chemotherapy were included, the effective response rate in the HRD group increased to more than 50%, indicating that this population is particularly sensitive to the combined approach.
The study also included extensive biomarker analyses to help determine why some patients benefited more than others. Tumors in the HRD group showed higher levels of genomic instability, including increased numbers of mutations known as frameshift insertions and deletions. These mutations can generate neoantigens, making cancer cells more visible to the immune system.
Consistent with this, HRD tumors also exhibited greater infiltration by immune cells, particularly tumor-infiltrating lymphocytes. Patients with higher immune cell presence and lower levels of circulating tumor DNA were more likely to experience durable disease control, in some cases lasting more than three years.
However, the relationship between tumor genetics and immune response was not straightforward. While HRD tumors tended to be more immunogenic, not all showed strong immune cell infiltration, suggesting that additional factors in the tumor microenvironment may limit immune activity. This complexity highlights the importance of combination strategies that not only increase tumor visibility but also overcome immune suppression.
Furthermore, the treatment regimen was generally well tolerated. There were no serious or unexpected safety issues reported, and the majority of side effects, including anemia and the occasional immune-related complications such as pneumonitis or colitis, were treatable.
The POLAR trial expands on previous research demonstrating that olaparib alone can slow disease progression in patients with BRCA-mutated pancreatic cancer, but without clear overall survival benefits. The researchers used pembrolizumab to improve immune recognition of cancer cells, taking advantage of the increased mutation burden associated with HRD.
While the study was small and not randomized, its findings provide a compelling case for further investigation. Ongoing and future trials will aim to confirm these results in larger populations and refine patient selection using biomarkers such as HRD status, neoantigen profiles, and circulating tumor DNA.
Ultimately, the results suggest that tailoring therapy based on tumor genetics, particularly DNA repair defects, could help identify patients most likely to benefit from emerging immunotherapy combinations. For a disease long defined by limited options, even incremental advances like these could have a meaningful impact on survival.
