“Identification and analyses of exceptional responders could eventually offer hints as to why PC is resistant to immunotherapy.”
Immunotherapy is not usually effective against pancreatic cancer (PC), but a new study published in Oncotarget (Volume 16, 2025) highlights rare cases where it did help. These examples, though uncommon, may offer valuable insights for future treatment.
Pancreatic Cancer and Immunotherapy
Pancreatic cancer is often diagnosed at an advanced stage, which limits treatment options and contributes to its poor prognosis. While chemotherapy remains the standard treatment, it usually offers only modest benefits in terms of survival. Immunotherapy—an approach that activates the immune system to fight cancer—has been effective in other cancers but has shown limited success in PC.
This is largely due to the tumor’s ability to suppress immune responses and create an environment that protects it from attack. Currently, these drugs are only approved for a small subset of patients whose tumors have a specific genetic feature called high microsatellite instability (MSI-high), found in just 1 to 2 percent of cases.
The Study: Pancreatic Cancer Immunotherapy Responders
The study, titled “Exceptional responders to immunotherapy in pancreatic cancer: A multi-institutional case series of a rare occurrence,” was led by first author Kavin Sugumar and corresponding author Jordan M. Winter, from University Hospitals Seidman Cancer Center.
The researchers examined medical records from 14 patients with pancreatic ductal adenocarcinoma (PDAC) who had responded unexpectedly well to immune checkpoint inhibitors—drugs that help reactivate immune cells to attack cancer. The drugs included PD-1 inhibitors such as pembrolizumab and nivolumab, CTLA-4 inhibitors like ipilimumab, and agents targeting tumor-associated macrophages. To find these rare cases, the research team contacted 471 oncologists from 91 major U.S. cancer centers between 2020 and 2021.
Most of the patients in this study had already tried chemotherapy, without lasting success. These patients received immunotherapy alone. They were selected because they showed either a reduction in tumor size on imaging or a drop in CA 19-9, a blood marker used to monitor PC.
This case series is the largest to focus exclusively on PC patients who responded well to immunotherapy. By excluding those who received chemotherapy simultaneously, the study aimed to isolate the effects of immune-based treatments alone.
The Results: Immunotherapy Shows Effectiveness in Both MSI-High and MSI-Stable Pancreatic Cancer
After starting immunotherapy, 82% of the patients showed a partial response, meaning their tumors became smaller. Around one-third of the patients had a meaningful decrease in CA 19-9 levels. On average, their disease remained stable for about 12 months, which is longer than typically seen with other treatments at this stage. Some patients lived for more than two years after beginning immunotherapy.
What stood out most was that more than half of these patients did not have MSI-high tumors. This challenges the current understanding that only MSI-high patients are likely to benefit from immunotherapy and suggests that other, less well-understood factors may also play a role.
The Impact: Expanding the Role of Immunotherapy in Pancreatic Cancer
Although this study includes only a small number of patients, the results suggest that immunotherapy may benefit more individuals with PC than previously assumed. While the standard of care still centers on chemotherapy, this case series shows that a small but meaningful group of patients—some without the usual MSI-high genetic marker—can respond well to immune-based treatments. These observations support the idea that immunotherapy may have a broader role in PC care.
Future Perspectives and Conclusion
These findings highlight the need to understand why certain PC patients respond to immunotherapy despite lacking known predictive markers like MSI-high. Exploring tumor biology, immune interactions, and patient-specific characteristics may help identify new indicators of response.
Although immunotherapy remains ineffective for most PC cases, rare outcomes like those in this study offer valuable clues. Investigating these exceptions more closely could support the development of more personalized and effective treatment approaches.
Click here to read the full research paper in Oncotarget.
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Oncotarget is an open-access, peer-reviewed journal that has published primarily oncology-focused research papers since 2010. These papers are available to readers (at no cost and free of subscription barriers) in a continuous publishing format at Oncotarget.com.
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