Comet is one of very few dogs worldwide to receive a stem-cell transplant for cancer treatment, rather than primarily for research. Cost of the therapy: $45,000.

The Bainbridge Island dog got the transplant last summer after developing lymphoma, a cancer of the lymph tissue. Now, after a long, steady recovery, he is showing signs of being cured.

The effort to save Comet involved dozens of dog lovers in five states and four countries, a renowned explorer in Honduras and a pioneering cancer center in Seattle.

His owners never flinched at the cost.

“It wasn’t even a close decision,” said Darrell Hallett, a Seattle attorney who with his wife, Nina, scrapped a kitchen remodel in favor of the retriever.

“How could I live with myself if I didn’t do this and he had a good shot at getting through it?” Hallett said. “When you take on a dog, you have an ethical and moral obligation to take care of him.”

Although Comet’s is an extreme case, it shows how far some people will go for their beloved companions. Pet owners may pay thousands for treatments once reserved for humans, including kidney transplants, gall-stone removal, hip replacements, and chemotherapy, radiation and surgery for cancer, said Dr. Sandy Wright, a representative of the American College of Veterinary Internal Medicine.

Spending on veterinary care, including such high-tech procedures, has steadily increased — from $7 billion in 1991 to an estimated $19 billion in 2001, the American Veterinary Medical Association said.

Comet’s transplant was performed by Bellingham veterinarian Dr. Edmund Sullivan. The stem cells came from a dog descended from the golden retriever of explorer Sue Hendrickson, internationally known for her 1990 discovery of the largest Tyrannosaurus rex skeleton ever found.

Hendrickson, a friend of the Halletts’, owns Comet’s mother and 11 other dogs at her home on a Honduran island. She spent months tracking down 40 of Comet’s relatives to donate blood that was tested for a stem-cell match.

Scientists at the Fred Hutchinson Cancer Research Center in Seattle donated key advice and facilities for the procedure, which has rarely been done strictly as therapy for dogs. The Hutch has performed hundreds of experimental bone-marrow or stem-cell transplants on dogs over the past 40 years, as researchers perfected the techniques now used worldwide to treat cancer in an estimated 40,000 people each year.

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