Her blue dress picked out and her travel arrangements secured, Catherine Holm was ready for her trip to Puerto Rico for her youngest son’s wedding.

But in the weeks leading up to Saturday’s ceremony, Holm, 58, of North Babylon, was “in and out” of the hospital with severe back and chest pain.

“No one could figure out what was going on,” she said, until the day before Easter, when doctors told her she had acute lymphoblastic leukemia — a fast-growing type of cancer that would require her to remain in the bone marrow transplant unit at Stony Brook University Hospital while her son Mark Holm Jr, 24,. tied the knot.

Some of the nurses in the unit, aware of Holm’s predicament, decided that if she couldn’t attend the wedding, they’d bring the wedding to her.

On Monday evening, Holm looked on — in that blue dress and with a surgical mask — as her son and daughter-in-law exchanged vows in the hospital’s chapel, surrounded by friends and family.

“It took my breath away just to know that I had the opportunity to be with my son and everyone to celebrate their marriage,” Holm said Tuesday.

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Holm’s daughter-in-law, Joanna (née Caldeira), said other leukemia patients and hospital staff, led by nurse manager Taylor Adamo, planned almost everything — providing the food, decorations and music for the small wedding.

“It was more than I could have ever asked for,” Joanna Holm, 24, of Deer Park, said. “We’re blessed to have had this opportunity, and so grateful for the hospital and everyone who’s helped.”

Guests were asked not to bring gifts, but instead to join the bone-marrow registry, in the hopes of finding a match for Holm, who’s in need of a transplant.

Each year, about 6,000 people in the United States are diagnosed with acute lymphoblastic leukemia. Only three in 10 patients will receive a potentially lifesaving bone marrow transplant, according to Stony Brook University Hospital.

The newlyweds are off Thursday to Puerto Rico, where they will have another ceremony. Upon their return, the couple plans to hold a donor registry drive at St. Paul’s Reformed Church in North Babylon, Joanna Holm said.

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“It still feels unreal that this would happen to such a great woman,” she said. “But we’re just trying to stay positive and are trying to get help from as many people as possible.”