To Dr. John Hansen, every patient was special.

“Every patient that I’ve known, every patient that I’ve helped … every one of them is a precious experience,” Hansen said in an interview in 2018.

Hansen, 76, died peacefully at his home on July 31 after a battle with pancreatic cancer.

Hansen left a huge mark on the bone marrow transplant community, with one of his most notable contributions being the National Marrow Donor Program, now known as Be The Match. He played an integral role in understanding how to find suitable donors for each transplant patient, establishing registries of these donors and started collections of biological samples and data that have become crucial resources for countless researchers worldwide.

He also served as a clinical researcher at the Fred Hutchinson Cancer Research Center in Seattle from 1977 until 2018 when he retired. There he and his team studied which combination of chemicals in a patient’s immune system is required to keep their body from rejecting a marrow transplant from a donor.

“The contributions that John made in the field of hematopoietic stem cell transplantation were extraordinary,” Dr. Gary Gilliland, the president and director of the Hutchinson center, said in a statement. “His work extended transplantation on a global scale. He invigorated this idea that we all need to support each other as a community — and that we all need to come together to think about ways to treat patients who have cancers that can be cured with bone marrow transplantation. Measured in the number of human lives saved, few physician-scientists have had the impact that he had during his lifetime and will continue to have.”

Hansen was part of Dr. E. Donnall Thomas’ team when he came to the center. At the time, bone marrow transplantation was a radical and experimental treatment for leukemia and other blood diseases. While it was unknown, it was thrilling to Hansen to be part of something revolutionary.

“It was so novel. And so exciting in terms of what it represented in terms of big breakthroughs,” Hansen said in 2018.

In 1979, Hansen helped perform the first successful bone marrow transplant for leukemia involving two unrelated people. The little girl who received the transplant, 10-year-old Laura Graves, ultimately died of her leukemia, but it inspired Hansen to work with her father—Dr. Robert Graves—in establishing a bone marrow registry. This soon became an international repository that contains samples and data from nearly 50,000 donor-recipient pairs.

“You can’t even begin to quantify how important that resource is,” Dr. Effie Wang Petersdorf, an HLA expert whose own research has relied on the repository, told Fred Hutch in a 2018 article. “Almost every major study that has sought to answer a question related to the importance of a gene or polymorphism has leveraged that resource.”

Hansen’s contributions to cellular therapy and beyond will have an impact for years to come. Colleagues said that he was an extraordinary man who stands among icons in the medical field.

“John was a scientific pioneer and a true gentleman,” said Dr. Nancy Davidson, senior vice president and director of the Hutch’s Clinical Research Division and holder of its Raisbeck Endowed Chair for Collaborative Research, president and director of Seattle Cancer Care Alliance, and head of the Division of Medical Oncology at the University of Washington School of Medicine. “Countless patients and families benefitted from his expertise and his compassion. I am grateful for his legacy to the field of stem cell transplantation and to Fred Hutch.”

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