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This Blood Test Detects Cancer in Dogs. But Do You Want to Know?

It was time for Cici Pepperoni’s annual check-up, but Marina Inserra, the 7-year-old pit bull mix’s owner, wasn’t worried. Inserra worked as a veterinary assistant at the San Diego office where Cici was getting her exam, and as far as she knew, Cici was perfectly fine.

Along with the checkup, Inserra agreed to enter Cici in a clinical study by a company called PetDx that had partnered with her office. The company wanted healthy dogs to donate blood to help validate a test to screen for multiple cancers at once—a liquid biopsy. “She didn't flinch at all,” Inserra says of Cici’s blood draw. “She was shaking in her boots a little bit, but she was happy to get a treat afterward.”

Cancer is the leading cause of death among dogs, especially old ones. About half of dogs age 10 and older die from cancer. A few types are particularly aggressive: lymphoma, in white blood cells; hemangiosarcoma, in blood vessels; and osteosarcoma, in bone. Routine tests like blood counts and urinalysis often miss the disease before symptoms set in, so vets usually can’t diagnose until it’s too late. Even if they do suspect a tumor, the surgical tests to confirm it can be invasive, expensive, and dangerous to vital organs.

“I've been being asked for so many years by families: Isn't there a blood test for cancer?” says Andi Flory, a veterinary oncologist who cofounded PetDx in 2019. Her cofounder, Daniel Grosu, a former chief medical officer with sequencing company Illumina, had experience developing liquid biopsies for people. Blood screens for lung cancer in humans first earned regulatory approval in 2016.

Flory and Grosu set out to develop the first multi-cancer liquid biopsy for dogs, which they called OncoK9. The product launched in 2021 and is available at about 400 veterinary clinics by prescription only. PetDx markets the test as a routine tool for older dogs and high-risk breeds, and for confirming suspected cancers when other evidence exists.

Today, in a paper published in PLOS ONE, they detail the performance of their liquid biopsy in a trial that began in 2019. Over about a year and a half, 1,100 dogs had their blood drawn by vets who had partnered with PetDx. Some dogs had cancer diagnoses already. The rest were presumably cancer-free. Then PetDx’s lab examined that blood using an in-house genomic analysis that looked for mutations or other biomarkers of cancer in the DNA that floats in the bloodstream. They concluded that, when analyzing blood from dogs known to have the three most aggressive canine cancers, their algorithm correctly sounded the alarm 85 percent of the time. It was more modestly effective overall, catching about 55 percent of total cases.

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The prospect of a blood-based cancer screen for dogs elicits both excitement and caution from veterinary experts and ethicists. “It might really help a lot of patients and could be really exciting,” says Lisa Moses, a veterinarian who specialized in palliative care for 30 years and is currently a bioethicist at Harvard Medical School. “But it really has to be carefully used.”

Because blood screens are noninvasive, they are safer and less expensive than surgery to confirm that a pet has cancer, especially for hard-to-reach tumors in the spleen or liver. But in cases where an early diagnosis still doesn’t offer much hope for treatment, is knowing sooner worth the stress?

When Flory and Grosu met in 2019, they didn’t talk business—they talked Poppy. Poppy was Grosu’s 8-pound, 4-year-old mixed-breed pup. You can guess by Flory’s oncology job that their paths crossed under lousy circumstances.

Poppy didn’t have a particularly high risk of tumors; purebreds like Golden Retrievers and older dogs are more susceptible. But here it was: an advanced-stage cancer, found too late. “There's not a lot that I can do, unfortunately, to manage it at this point,” recalls Flory.

It was a particularly difficult blow to Grosu; both of his parents had received cancer diagnoses the year prior. “Cancer fights hard, and it fights unfairly. It comes after you, comes after your family, comes after your dog,” he says. “Poppy’s diagnosis was kind of the last straw for me … At some point, you feel like you need to fight back.”

Grosu’s idea for a screening test was based on cell-free DNA, or cfDNA. As cells and DNA degrade naturally, fragments can chip off, leaving traces in the bloodstream like crumbs. Diseases like cancer may increase cfDNA levels. If you sequence that cfDNA, you can identify the genetic material of the healthy cell or tumor that shed it.

For an OncoK9 test, once the vet draws blood, they ship it to PetDx’s lab, where staff centrifuge it to separate the plasma, then mix the plasma with special beads that stick to cfDNA and isolate it. They then sequence the genetic material and run the sequence through an algorithm that looks for changes previously associated with human and canine cancers, including mutations and extra or missing segments of chromosomes—known as copy number variations.

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This algorithm has been designed to spot these genetic indicators across many dog breeds with different forms of cancer: say, a bloodhound with lymphoma or a golden retriever with hemangiosarcoma. When the PetDx team began their study, they used blood from 224 of the dogs—ones known to either have cancer or not—to refine their algorithm. This “training set” helped PetDx determine a threshold for each genomic variation, defining what they should call signal rather than just noise.

Then they unleashed the algorithm onto data from the 876 other dogs. For each, it would render a binary answer: yes cancer, or no cancer. (For most cancers, it wouldn’t identify which form it was.) Pet owners and vets already knew whether their dogs had a cancer diagnosis, but the PetDx researchers did not, so as to not influence their analysis. The team then compared their results to the vets’ previous diagnoses.

Overall, the algorithm caught about 55 percent of the total cases, representing 30 varieties of cancer. It was most accurate when identifying late-stage cancers, or any stage of aggressive types. For the three most aggressive cancers, OncoK9 gave the right answer 85 percent of the time. For all metastatic cancers, the figure was over 80 percent. For the eight most lethal cancers, it was 62 percent. “Any of these numbers,” says Flory, “are a huge improvement over what the current paradigm is.” She estimates that’s between 3 and 10 percent for early-stage cancers.

Cici Pepperoni turned out to be one of the positive tests—a surprise to Inserra and their vet. The company notified the vet, who scheduled scans in May 2021 that revealed growths in the dog’s lungs and a mass in her heart. “We realized, oh my gosh, not only does she have cancer, but she has a lot of cancer,” Inserra says.

It turned out to be hemangiosarcoma—a death sentence. Hemangiosarcoma generally makes itself known as an emergency, when a tumor suddenly bleeds into the space around the dog’s heart. “They're collapsed. They have anemia. They're bleeding,” says Flory. Their family must rush to get help. “All of a sudden, they're at the ER clinic having to really make this life or death decision.”

But since OncoK9 caught Cici’s case many months early, Inserra’s family had options. They could try palliative care to lower the risk of bleeding, or chemo to maybe shrink the tumor. They chose the former to keep Cici more comfortable. By July, she had unmistakable symptoms. Weight loss. Coughing. “She started getting a little bit more spacey,” Inserra says. The vet noticed fluid in her chest. Inserra’s family prepared to say goodbye.

They brought Cici to San Diego’s Dog Beach so she could run around and have fun as best she could. They brought the most desirable treats they could find, including, of course, pepperoni pizza. She wasn’t eating much anymore, but Cici didn’t disappoint: “She took one little bite,” Inserra says. “That was our happy last moment.”

Cici’s case illustrates the thorny ethical debate over early cancer diagnoses for dogs. Dogs don’t have as many treatment options as people do. And blood tests still need to be confirmed by imaging and biopsies, so pet owners who can’t afford more testing may opt to just wait and see. “If it works, it's going to be fantastic for the dogs,” says Elinor Karlsson, a computational biologist with the University of Massachusetts Medical School who studies the genomics of dog diseases. (Karlsson is not involved with PetDx and is an unpaid scientific adviser for canine cancer analysis startup FidoCure.) But we have to be careful, Karlsson says: “Are you just stressing a lot of people out without being able to help?”

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Karlsson also notes that, despite catching Cici’s case early, the PetDx test misses most smaller and localized cancers. In the study, it detected only 51 percent of local lesions bigger than 2 inches—and 20 percent of smaller ones.

False positives appeared in up to 1.5 percent of the 519 cancer-free dogs. That’s a small number—but not none. And it’s why Moses, the Harvard bioethicist, worries about using a blood test as a routine checkup tool. False positives can push owners and vets to order follow-up exams “on a patient that doesn't need them,” Moses says. “Worst, worst, worst-case scenario is somebody misinterpreting how the test works and using it as a basis for deciding on euthanasia.”

It’s too early to count on OncoK9 to catch cancers early, agrees Vilma Yuzbasiyan-Gurkan, a molecular geneticist and small-animal clinical scientist from Michigan State University. “I'm very enthusiastic about this” as a technology, she says, noting that the impressive size of this trial makes it a good first step. But she and Karlsson were both disappointed that some details about the algorithm and its genomic targets remain confidential. And both want more data on how screening blood can actually improve outcomes. “It has great potential,” she says, but is “a little overstated.”

In December 2021, PetDx began a new study to follow more than 1,000 cancer-free dogs with biannual blood screens. Grosu hopes this “lifetime assessment” will prove whether OncoK9 can reliably catch cancers early.

Midway through the study, the pet supply retailer Petco made a $10 million investment in PetDx. Petco offers the test in more than 60 of its full-service veterinary clinics, but representatives from both companies said that Petco had no influence on the research. "There were no Petco/Vetco sites in the study. Petco became involved with PetDx as an investor in August 2020. By that time, our clinical collections were well underway and most study sites had been contracted already," Flory wrote in an email to WIRED. "Petco was not involved in reviewing the study results."

“Petco was not involved in preparing or reviewing the scientific results or write-up, but we continue to track the progress PetDx is making with their groundbreaking research,” Whitney Miller, Petco’s chief veterinarian, wrote in an email to WIRED.

While canine cancer experts worry about the ethics of using the test too broadly, PetDx recommends it only for a few use cases: for dogs at high risk and as diagnostic aid when vets suspect cancer. PetDx hopes to expand use to monitoring cfDNA during cancer treatment, to track how the treatment is helping.

For her part, Moses, the vet and bioethicist, does think that having a diagnosis beats not having it, even if a dog’s cancer is incurable. “I think for most people it’s actually helpful and comforting,” she says. “I've rarely had people say, ‘I wish I didn't know.’”

Inserra agrees. She’s happy Cici’s diagnosis happened the way it did, and she’s grateful to have had time to prepare. “It's hard knowing you're going to lose your dog, but you don't know when,” Inserra says. “I'd rather have that, and cherish the time that we have with her, than one day lose her and not know that she had cancer.”


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