Liquid biopsy allows earlier detection of canine cancer

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As the leading cause of death in canines over 1 year of age, cancer is a word that strikes an emotional chord in pet owners and veterinarians alike. Unfortunately for many dogs, cancer is not detected until patients are exhibiting clinical signs and disease is advanced. During a session at the 2023 American College of Veterinary Internal Medicine (ACVIM) Forum in Philadelphia, Pennsylvania,¹ Andi Flory, DVM, DACVIM (oncology), co-founder of PetDX, shared that, she “was sick of seeing dogs where the cancer was detected way too late.” The desire to improve veterinarian’s ability to detect cancer drove her to research liquid biopsy, which she has spent the last 2 years studying.

Improving cancer detection through liquid biopsy

“When we can find [cancer] at an earlier stage, our ability to cure or extend life is highest,” shared Flory. In a retrospective review of 350 dogs with a diagnosis of cancer, only 12% were diagnosed prior to the onset of clinical signs.² The remaining 88% of dogs had clinical signs that prompted a “diagnostic odyssey” resulting in a cancer diagnosis.²

In human medicine, liquid biopsy is used for various applications related to cancer screening, diagnosis, and monitoring. With over 10,000 publications in the human medical literature over the last 10 years, Flory notes that the technology is growing rapidly, and “it makes sense we adopt this technology on the vet side as well.”

When cells die, they shed their DNA into the blood, where it is broken into fragments, called cell-free DNA. Neoplastic cells leak DNA containing genetic mutations specific to the tumor of origin. This DNA is not found in cells affected by inflammation or infection, making it a unique marker of cancer. The liquid biopsy developed by PetDX, called OncoK9, utilizes next generation sequencing to identify this DNA, called a cancer signal, in canine blood samples. Detection of a cancer signal indicated that tumor cells were present in the dog’s body at the time of blood collection.

In a clinical validation study that evaluated over 1,100 dogs, the test was found to have a 54.7% sensitivity and 98.5% specificity for neoplasia, detecting over 30 types of cancer.³ This sensitivity and specificity remained similar in a retrospective analysis of 1,500 real-world cases, at 61.5% and 97.5%, respectively.⁴ Three of the most aggressive canine cancers—osteosarcoma, hemangiosarcoma, and lymphoma—had a detection rate of 85.4% in the clinical validation study.³

Currently, the standard of care for cancer screening in asymptomatic patients is a routine physical examination, performed every 6 to 12 months. In some cases, screening lab work is performed concurrently, which may include a CBC, Chemistry panel, and urinalysis. OncoK9 offers “a big improvement over the status quo,” said Flory. In an evaluation of dogs with a known cancer diagnosis, OncoK9 detected a cancer signal in 48% of dogs who were diagnosed with cancer pre-clinically, compared to only 12% of dogs where cancer was detected during wellness or other preventive care evaluations.² In a retrospective study of real-world cases, 26 different cancer types were diagnosed, and at least half of these would be difficult or impossible to detect during a routine physical examination.⁴

“Incorporating liquid biopsy into preventive care can improve cancer detection,” concluded Flory. Detection rates are higher for disseminated cancers than for localized cancers, which are often easier to detect on a routine physical examination. Liquid biopsy not only improves detection, it also “expands the number and types of cancer we can detect in asymptomatic patients.”

Veterinary applications for liquid biopsy

Liquid biopsy can be used both before and after a cancer diagnosis. Prior to a diagnosis, the test can be used to screen asymptomatic patients who are at higher risk for cancer or as a diagnostic aid during the work-up of a patient with clinical signs consistent with cancer. OncoK9 can also be used to monitor cancer and predict recurrence, which is an area of ongoing study.

The most common use is as a screening test, with 64% of samples received falling into this category.³ Flory recommends that screening be instituted two years prior to the median age at cancer diagnosis. For most breeds, this is between 8 and 9 years of age, but for some higher-risk breeds, such as the Golden Retriever, Bernese Mountain Dog, and more, the median age is closer to 6. “Ultimately, [I] recommend using this as a screening test at age 7 but could be as early as age 4,” said Flory.

After a cancer signal is detected, veterinarians should pursue a “confirmatory cancer evaluation,” including a thorough physical examination (including oral and rectal evaluation), laboratory analysis, imaging of the chest, abdomen, and any areas of orthopedic pain, and aspirates of any abnormalities found. Most of these tests can be performed by general practitioners, allowing for a rapid diagnosis.

Flory noted some key takeaways for those using liquid biopsy in practice. “I can’t stress how important it is to fill the tube above the minimum fill line,” said Flory. The test does require a large volume of blood, which is safe to remove from canine patients at a single time.

Additionally, it is essential to educate clients that the test looks for the presence of cancer at the time of the test, providing a snapshot in time. It does not predict future cancer, so when it is used as a screening test in asymptomatic patients, it should be repeated over time.

Take home points

Liquid biopsy offers a new tool that veterinarians can use for the detection of multiple types of cancer in at-risk but asymptomatic patients, as a diagnostic aid when cancer is suspected, and as a cancer monitoring tool. Patient outcomes will improve because of earlier detection.

References

1. Flory A. Two years of liquid biopsy testing in dogs. Presented on June 17, 2023. ACVIM Forum 2023. Philadelphia, PA.
2. Flory A, McLennan L, Peet B, et al. Cancer detection in clinical practice and using blood-based liquid biopsy: A retrospective audit of over 350 dogs. J Vet Intern Med 2023 Jan;37(1):258-267. doi: 10.1111/jvim.16616. Epub 2023 Jan 20.
3. Flory A, Kruglyak KM, Tynan JA, et al. Clinical validation of a next-generation sequencing-based multi-cancer early detection “liquid biopsy” blood test in over 1,000 dogs using an independent testing set: The CANcer Detection in Dogs (CANDiD) study. PLoS ONE 2022;17(4): e0266623. https://doi.org/10.1371/journal.pone.0266623
4. O’Kell AL, Lytle KM, Cohen TA, et al. Clinical experience with next-generation sequencing–based liquid biopsy testing for cancer detection in dogs: a review of 1,500 consecutive clinical cases, JAVMA 2023;261(6), 827-836. https://doi.org/10.2460/javma.22.11.0526