Cancer is the main cause of death in dogs, particularly in the elderly. It kills almost half of all dogs over the age of ten. Lymphoma, which affects white blood cells, hemangiosarcoma, which affects blood vessels, and osteosarcoma, which affects bones. Tare three forms that are extremely aggressive. Routine testing such as blood counts and urine frequently miss the disease before symptoms appear. Therefore veterinarians are often unable to diagnose the disease until it is too late. Even if a tumour is suspected, surgical procedures to confirm it can be invasive, costly, and harmful to important organs.
“I’ve been asked this question by families for years: Isn’t there a blood test for cancer?” says Andi Flory, a veterinary oncologist and cofounder of PetDx, along with Daniel Grosu, her cofounder and former chief medical officer of sequencing company Illumina who had experience producing liquid biopsies for humans. The first blood tests for lung cancer in humans were approved by the FDA in 2016.
Flory and Grosu set out to create OncoK9, the world’s first multi-cancer liquid biopsy for dogs.
The product was introduced in 2021 and is exclusively available by prescription at roughly 400 veterinary clinics. The test is marketed by PetDx as a routine tool for older dogs and high-risk breeds, as well as for confirming cancer suspicions when other evidence is available.
They describe the performance of their liquid biopsy in a trial that began in 2019 in an article published today in PLOS ONE. Over the course of a year and a half, 1,100 dogs had their blood extracted by PetDx-partnered veterinarians. Some of the dogs had previously been diagnosed with cancer. The rest appeared to be cancer-free. The blood was then analysed by PetDx’s lab, which used an in-house genomic analysis to hunt for mutations or other cancer biomarkers in the DNA floating in the bloodstream. They found that their system accurately raised the alarm 85 percent of the time when analysing blood from dogs with the three most severe canine malignancies. Overall, it was only marginally effective, catching roughly 55% of all instances.
Veterinary professionals and ethicists are both excited and concerned about the prospect of a blood-based cancer screening for dogs. Lisa Moses, a veterinarian who specialised in palliative care for 30 years and is now a bioethicist at Harvard Medical School, adds, “It might actually help a lot of patients and might be incredibly exciting”. “However, it must be taken with caution”.
Blood tests are safer and less expensive than surgery to confirm if a pet has cancer, especially for hard-to-reach tumours in the spleen or liver, because they are noninvasive. Is knowing sooner worth the stress in circumstances where an early diagnosis still doesn’t give much chance for treatment?
Fragments of cells and DNA can break off as they decay naturally, leaving crumbs in the bloodstream. Cancer and other diseases may cause a rise in cfDNA levels. You can determine the genetic material of the healthy cell or tumour that released the cfDNA by sequencing it.
When a vet draws blood for an OncoK9 test, the blood is sent to PetDx’s lab, where it is centrifuged to extract the plasma, then mixed with special beads that cling to cfDNA and isolated. They next sequence the genetic material and run it through an algorithm that searches for abnormalities previously linked to human and canine malignancies, including as mutations and excess or missing chromosome segments (also known as copy number variations).
This algorithm was created to detect these genetic markers in a variety of dog breeds with various cancers, such as a bloodhound with lymphoma or a golden retriever with hemangiosarcoma. When the PetDx team started its research, they collected blood from 224 dogs, both cancerous and non-cancerous, to fine-tune their algorithm. This “training set” assisted PetDx in determining a threshold for each genetic variant, defining what should be referred to as signal rather than noise.
The technique was then applied on data from the other 876 dogs. It would return a binary answer for each: cancer yes or cancer no. (It wouldn’t tell you the type of cancer you had for most malignancies.)
Up to 1.5 percent of the 519 cancer-free canines had false positives. Overall, the algorithm caught around 55% of all cases, which included 30 different types of cancer. It was most effective at detecting late-stage malignancies, as well as any stage of aggressive tumours. OncoK9 correctly predicted three of the most aggressive tumours 85 percent of the time. The rate was over 80% for all metastatic malignancies. It was 62 percent for the eight most fatal malignancies.