Truman’s owners first thought he had twisted his ankle: The Bernese mountain dog was limping and might have landed awkwardly after jumping off the couch. But when he was still hobbled a few days later, they got an x-ray. The scan revealed that Truman had osteosarcoma, a deadly, fast-moving bone cancer that typically strikes breeds of large dogs. The owners’ veterinarian told them amputating Truman’s leg, followed by chemotherapy, might buy them another year or so with their fun-loving clown. They opted for the surgery and took one important extra step: enrolling him in a clinical trial at Tufts University that was studying an experimental vaccine for osteosarcoma. Nearly two years since his diagnosis, Truman remains cancer-free. He gets along fine with three legs and turned nine early this month, which he celebrated with a car ride and dog-friendly carrot cake.

Life, at long last, is improving for dogs with cancer, the number-one killer of beloved pets. An estimated one in three dogs get the disease. Some pure breeds, such as golden retrievers and boxers, are especially prone to it. Yet for decades, there was scant research into canine cancer, and consequently, veterinarians had little to offer sick pets and their distraught owners.

That situation has begun to change since researchers realized that dogs might be able to solve some of the mysteries of human cancer. Several scientists believe pet dogs are better research models than lab mice for this disease, as well as some other illnesses. Our dogs share our lives, drinking the same water and breathing the same air. Their diseases occur naturally like ours, as opposed to being introduced artificially in lab mice. We also have more in common with dogs biologically than we do with mice, and cancer is often caused by the same genetic mutations in both species.

Those factors are why clinical trials using pet dogs have increased over the past decades, especially in oncology. These tests examine new therapies for canine cancer that might inform research in human cancer treatment. The National Cancer Institute, an arm of the U.S. National Institutes of Health, has been a major supporter of this new work. In 2017 the NCI gave out $11.5 million in grants to six veterinary schools to study immunotherapy treatments for four different cancers in pet dogs. NCI funding, plus more from pharmacological companies, has made for boom times in canine cancer research. “Dogs are helping us understand a very complex puzzle,” says Amy LeBlanc, a veterinary oncologist who directs the Comparative Oncology Program at the NCI. “Not only do we have more research, but the sophistication of that research has exploded.”

Though the overarching goal of these comparative trials is to help humans, they have produced a number of promising cancer drugs for dogs. In 2017 the U.S. Food and Drug Administration conditionally approved Tanovea-CA1 to fight canine lymphoma. And an osteosarcoma vaccine under development by Aratana Therapeutics has been conditionally approved by the U.S. Department of Agriculture. Other drugs are well along in the clinical study pipeline, such as verdinexor for treating lymphoma in dogs.

New treatment techniques and diagnostic tools have likewise been created. Technology for targeted radiation that avoids damaging tissue near a tumor was developed on pet dogs with sinus tumors at the University of Wisconsin–Madison. Now the next generation of that therapy, Radixact, works on a wider range of tumors, even ones that move, such as in lung cancer, says David Vail, a professor of veterinary oncology who designs comparative clinical trials at the university. And a new liquid biopsy has made canine bladder cancer, which can be mistaken for bladder stones or urinary tract infections, easy to diagnose, even in an early stage. Developed by a team at North Carolina State University, the technique screens for the tell-tale signs of cancer in a urine test.

Genetic research into canine cancer, which has lagged far behind the human version, has gotten a boost as well. The DNA of canine osteosarcoma cells was sequenced this past summer by researchers at Tufts. The NCI has given money to sequence DNA for at least five other canine cancers, including melanoma, B-cell lymphoma and bladder cancer. Cheryl London, a veterinary oncologist at Tufts and an expert in comparative oncology, predicts that the next five years will see an explosion of genetic information, and that will lead to more effective and less toxic treatments for dogs with cancer.

These clinical trials have also given owners with dangerously sick dogs somewhere to turn. The osteosarcoma vaccine study that helped Truman was run by the NCI at 11 universities. Not only do these trials provide experimental medicine that may save a dog’s life, most do it at a price any dog owner can afford: free. “We now have access to some of the latest and greatest cutting-edge medicine for dogs,” says Nicole Ehrhart, a veterinarian at Colorado State University who helped pioneer limb-salvaging techniques for dogs with bone cancer.

The boom in canine cancer research has inspired some scientists to think very big. This past spring, the largest veterinary clinical study in history began to test a vaccine meant to stop any type of cancer before it becomes a tumor. By its conclusion, 800 dogs will have been injected with the boosters or a placebo and tracked for five years. And Ehrhart, who also directs Colorado State University’s Columbine Health Systems Center for Healthy Aging, is devising studies with pet dogs to better understand old age, which she calls the root problem of cancer. “This it where it gets exciting and futuristic,” Ehrhart says. “If we could slow down aging, we would make such impact on these diseases.”

People would also have their pets longer—the dream of anyone with a dog curled up at their feet, especially a sick one. “What people forget about veterinary medicine,” London says, “is that I’m also treating the person on the other end of the leash.”