Researchers at Memorial Sloan Kettering Cancer Center in New York, led by Dr. Vinod Balachandran, extracted patients’ tumors and shipped samples of them to Germany. There, scientists at BioNTech, the company that made a highly successful Covid vaccine with Pfizer, analyzed the genetic makeup of certain proteins on the surface of the cancer cells.

Using that genetic data, BioNTech scientists then produced personalized vaccines designed to teach each patient’s immune system to attack the tumors. Like BioNTech’s Covid shots, the cancer vaccines relied on messenger RNA. In this case, the vaccines instructed patients’ cells to make some of the same proteins found on their excised tumors, potentially provoking an immune response that would come in handy against actual cancer cells.

“This is the first demonstrable success — and I will call it a success, despite the preliminary nature of the study — of an mRNA vaccine in pancreatic cancer,” said Dr. Anirban Maitra, a specialist in the disease at the University of Texas MD Anderson Cancer Center, who was not involved in the study. “By that standard, it’s a milestone.”

The study was small: Only 16 patients, all of them white, were given the vaccine, part of a treatment regimen that also included chemotherapy and a drug intended to keep tumors from evading people’s immune responses. And the study could not entirely rule out factors other than the vaccine having contributed to better outcomes in some patients.

“It’s relatively early days,” said Dr. Patrick Ott of the Dana-Farber Cancer Institute.

Beyond that, “cost is a major barrier for these types of vaccines to be more broadly utilized,” said Dr. Neeha Zaidi, a pancreatic cancer specialist at the Johns Hopkins University School of Medicine. That could potentially create disparities in access.