Adding Immunotherapy to Chemotherapy Before Pancreatic Surgery: Safe, Promising for Some,

Pancreatic cancer is one of the few cancers where immunotherapy - a treatment that has transformed outcomes in lung cancer, melanoma, and several other solid tumors - has largely failed to deliver. The tumor microenvironment in pancreatic cancer is densely immunosuppressive: thick stromal tissue walls off tumors from immune cells, and the immune cells that do infiltrate are often functionally exhausted. Still, the logic for trying immunotherapy before surgery in patients whose tumors might be removable is compelling.

A UCLA investigator-initiated clinical trial tested this logic in borderline-resectable pancreatic cancer - tumors that encroach on major blood vessels, making surgical removal technically possible but difficult. The study, published in Nature Communications in February 2026, enrolled 28 patients who received modified FOLFIRINOX chemotherapy combined with nivolumab, a PD-1 checkpoint inhibitor, before planned surgical resection.

What the Trial Found

The combination was well tolerated. No serious immune-related adverse events were attributed to nivolumab, and no treatment-related surgical delays occurred. Of the 28 enrolled patients, 79 percent proceeded to surgery. Among those who reached the operating room, all had their tumors successfully removed. Surgical margin status was favorable: 86 percent had clear (R0) margins, and 50 percent showed no cancer in their lymph nodes at the time of resection.

Those numbers compare reasonably to historical benchmarks for chemotherapy-alone approaches in borderline-resectable disease. But the headline result the trial was designed to demonstrate - improved overall survival - did not materialize. Survival outcomes for most patients were similar to what would be expected with standard chemotherapy alone.

The exception was a subset. Nine percent of patients had complete pathologic responses at surgery - no detectable cancer remaining when the resected specimen was analyzed. An additional 9 percent had near-complete responses. For these patients, outcomes were exceptional: unusually deep and durable disease control, including long-term disease-free survival in some cases.

Why Immunotherapy Works for Some and Not Others

The study's translational component - comparing pre-treatment biopsies against surgical specimens and against historical samples from patients who received chemotherapy alone - offers the most scientifically valuable findings. The immune landscape analysis used gene expression profiling, immunohistochemistry, and spatial transcriptomics to characterize changes in the tumor microenvironment produced by the combined treatment.

Adding nivolumab increased CD8 T cell infiltration in tumors - the anti-tumor immune cells whose activity checkpoint inhibitors are designed to enhance. That signal is what the combination was intended to produce. But the analysis also found two changes that may explain why the immune activation did not translate to broader survival benefit.

First, the treatment was associated with disorganized immune cell clusters. Effective anti-tumor immunity depends not just on the presence of immune cells but on their spatial organization. The treated tumors showed scattered, disorganized infiltrates rather than structured tertiary lymphoid structures that support sustained immune responses.

Second, the combination was associated with accumulation of plasma cells and T cell exhaustion. Exhausted T cells express high levels of inhibitory receptors and lose their ability to kill tumor cells effectively, even when present in large numbers. This is a distinct failure mode from T cell absence.

"By testing this novel drug combination in the preoperative setting, we were able to directly compare pre-treatment biopsies with surgical resection specimens to better understand why the therapy works in some patients, and, just as importantly, why it does not in others," said senior author Timothy Donahue, MD, chief of surgical oncology at the David Geffen School of Medicine at UCLA and director of the UCLA Agi Hirshberg Center for Pancreatic Diseases.

Implications for Future Trials

The immune analysis provides specific targets for improving future combination strategies. Approaches that prevent or reverse T cell exhaustion - combination with other checkpoint inhibitors targeting LAG-3 or TIM-3, or with agents that reshape the tumor stroma - could potentially expand the fraction of patients who achieve the deep responses seen in the responding 18 percent. Identifying which patients are most likely to respond before treatment starts is the other research priority.

The trial's small size - 28 patients - limits the statistical conclusions that can be drawn, and the single-arm design means all comparisons are against historical benchmarks. A larger randomized trial would be needed to definitively determine whether the combination improves outcomes for any identifiable patient subgroup.