A vitamin D-like drug already approved by the Food and Drug Administration for kidney disease may have found a way past one of the biggest obstacles in treating pancreatic cancer, the thick fibrous shield that surrounds tumors and blocks chemotherapy from reaching cancer cells.
In a randomized trial published May 25, 2026 in Nature Cancer, researchers at Dana-Farber Cancer Institute and the Salk Institute reported that paricalcitol, added to standard chemotherapy, safely reduced the activity of fibroblasts that build this protective barrier in 36 patients with previously untreated metastatic pancreatic cancer.
The trial tested paricalcitol on top of the two-drug chemotherapy regimen gemcitabine and nab-paclitaxel. Patients were assigned to placebo, intravenous paricalcitol, or oral paricalcitol. The main purpose was to check safety, not to prove the drug works, and the study was too small to draw efficacy conclusions.
Why pancreatic tumors are so hard to hit
Pancreatic tumors grow inside a dense mesh of connective tissue and fibroblasts that walls off the cancer cells. That mesh, known as the stroma, limits how much chemotherapy can reach the tumor and suppresses the immune cells that would otherwise attack it.
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It is a major reason pancreatic cancer remains among the deadliest common cancers. The American Cancer Society reports a five-year relative survival rate of just 3 percent for people whose disease has already spread to distant parts of the body at diagnosis.
Paricalcitol is a synthetic vitamin D analog that activates the vitamin D receptor, and it is approved to prevent and treat secondary hyperparathyroidism in people with chronic kidney disease. The idea to redirect it against pancreatic cancer grew out of a decade of preclinical work at the Salk Institute suggesting that turning on the vitamin D receptor could calm the fibroblasts driving the stromal shield.
What the trial actually showed
According to a Salk Institute release accompanying the study, adding paricalcitol was manageable in terms of side effects, though 5 of the 12 patients on the oral form developed elevated blood calcium that had to be controlled with dose adjustments. Tumor biopsies showed less fibroblast activation and more T cells infiltrating the tumor, matching what the lab work had predicted.
Partial tumor responses were seen in 10 of 24 patients who received paricalcitol, compared with 1 of 12 who received placebo. Five patients on paricalcitol had not progressed at one year, while none in the placebo group had reached that mark.
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Patients whose tumors expressed high levels of the vitamin D receptor and who received paricalcitol had the longest overall survival in the trial. Because the trial enrolled only 36 people, these numbers are signals worth chasing in a larger study, not proof of benefit.
"This study really takes a novel approach for cracking therapeutic resistance in pancreatic cancer," said Ronald Evans, a professor at the Salk Institute whose lab did the original vitamin D receptor work. "By using vitamin D analogs to engage the body's own natural system for dampening fibrotic and inflammatory responses, we can enable other therapies to do their job."
Kimberley Perez, a medical oncologist at Dana-Farber who helped lead the trial, said the findings support the idea of using a vitamin D analog to remodel the stroma so that other treatments can reach the tumor.
What this could mean for patients
Because paricalcitol is already approved for another condition, its safety profile is known and its manufacturing is established. That, at least in theory, could shorten the timeline if larger trials confirm a benefit.
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The next step is a bigger phase trial designed to measure survival, not just safety. Anyone with a pancreatic cancer diagnosis considering enrollment in a trial should talk with their oncologist before making changes to treatment.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.