Cancer Screening Blood Tests for Dogs: What a Result Means
The leading dog cancer blood test found about half of cancers in its own validation study. What a positive and a negative mean, and what's still unproven.
Written by thecanineledger
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In the largest published validation of a dog cancer blood test, “the liquid biopsy test demonstrated a 54.7% (95% CI: 49.3–60.0%) sensitivity and a 98.5% (95% CI: 97.0–99.3%) specificity” (Flory et al., PLOS ONE 2022). In plain terms, it found just over half of the cancers, and it rarely flagged dogs that were thought to be cancer-free. The study was funded by the test’s developer.
While a test that rarely gives false alarms is useful, a test that misses nearly half of cancers can’t rule cancer out. And nobody has yet shown that screening healthy dogs helps them live longer. This page explains what these tests measure, what a result means, and what to ask your vet.
1. What these tests look for
Bits of tumour in the blood. Blood carries free-floating DNA, and some of it comes from tumour cells. One type of test reads this DNA for “cancer-derived genomic alterations”. That’s the test in the 2022 study above.
Nucleosomes. A second type measures nucleosomes, which the 2022 nucleosome study describes as “small fragments of chromosomes released into the blood during cell death or white blood cell activation.” Levels are often raised in some cancers. But they also rise in other conditions. The same study notes that “increased plasma nucleosomes have been detected in cases of autoimmune disease and severe inflammation” (Wilson-Robles et al., BMC Veterinary Research 2022).
Neither test says where the cancer is. A positive result leads to more tests to find it.
Our note: We’ve described the two kinds of test in general terms and named no product.
2. The DNA test: what the validation found
Good at some cancers, poor at others. For lymphoma, haemangiosarcoma and osteosarcoma, “the detection rate was 85.4%”. Across eight common cancers, it was 61.9%.
Poor at small, local cancers. For cancers that hadn’t spread, detection was 19.6% for lesions of 5 cm or smaller, and 51.3% for larger ones. The authors say a small, reachable lump “should likely be pursued with conventional tissue sampling rather than with liquid biopsy”.
The control dogs weren’t all healthy. The authors explain that “the specificity of the test was not determined in a cohort of “healthy” dogs.” They used dogs presumed to be cancer-free, many with other illnesses. That’s a fair test of real-world use.
A newer version. A 2024 study by the same group combined a simpler blood measure with the DNA test, for seven named cancer types. It reported a sensitivity of 71.3% at a specificity of 98.7% (Flory et al., Journal of the American Veterinary Medical Association 2024, abstract). That figure covers only those seven cancers.
3. The nucleosome test: what the validation found
About half again. In over 500 dogs with cancer, “The sensitivity of increased circulating nucleosome concentrations for the detection of cancer in all dogs was 49.8% with a specificity of 97%”.
Strong for blood cancers. It “correctly identified 82% of hemangiosarcoma cases and 74% of lymphoma cases”.
Weak for common skin cancers. “Overall, the assay was only able to correctly predict 19% of the cases with mast cell tumors.” For melanoma of the skin, sensitivity was 0%.
Disclosure. Several authors are employees of the test’s developer, which holds patents on the technology.
4. What a positive result means
It depends on how common cancer is in dogs like yours. The 2022 authors explain that the positive predictive value (PPV), the chance a positive is a real cancer, is “arguably a more relevant number for clinicians” than sensitivity.
Their estimate assumes a high-risk group. For screening, they assumed “a conservative annual incidence of cancer in this screening population may be estimated at 8–10%”. On that basis, “the PPV is estimated to be 76–80%.”
In lower-risk dogs, more positives would be false. If fewer dogs in the group have cancer, the same test gives a lower PPV. A young dog of a low-risk breed is not the population the estimate was built for.
Our note: The 8–10% annual incidence is the developer’s assumption. We haven’t found an independent figure.
5. What a negative result means
It doesn’t rule cancer out. With about half of cancers missed overall, and four in five small local cancers missed, a negative result is not an all-clear.
A lump still needs a needle. If you find a lump, a negative blood test is no reason to skip having it sampled.
Our note: The 2022 authors estimate that 95–96% of negative results are correct, using their 8–10% assumption. We’ve stressed missed cancers instead, because a negative result is not reassurance about a lump you’ve found.
6. Does screening help dogs live longer?
Not yet known. The 2022 authors say long-term studies are still needed to understand “the ultimate clinical utility of earlier detection (including impact on clinical management decisions, and actual survival benefit after accounting for lead-time bias)”.
Lead-time bias means a cancer found earlier looks like it was survived longer, even if the dog dies at the same age. Only a study that follows screened and unscreened dogs can show a real benefit.
A long-term study has started. The authors describe one launched in December 2021. It aims to follow over 1,000 dogs, testing them twice a year. We found no published results on survival.
Our note: We couldn’t find results from the long-term study or any independent trial of screening outcomes.
7. What to ask your vet
- What would we do differently if the result is positive, or negative?
- How common is cancer in dogs of my dog’s age and breed?
- What further tests would a positive lead to, and what would they cost?
- Is this test meant for screening a healthy dog, or for a dog you already suspect has cancer?
→ Found a Lump? Why Your Vet Should Put a Needle in It · → Lymphoma: What Chemotherapy Can and Can’t Do · → Preventive Care Without the Upsell: What Your Dog Actually Needs
8. What we could not verify
| Commonly said | What we found |
|---|---|
| “A blood test can catch cancer early” | Sometimes. The leading DNA test found about half of cancers, and few small local ones. |
| “A negative result means no cancer” | No. Many cancers are missed, especially small ones. |
| “A positive result means cancer” | Usually, in high-risk dogs, on the developer’s estimate. Less often in low-risk dogs. |
| “Screening helps dogs live longer” | Unproven. No published study shows a survival benefit yet. |
| “These tests find all common cancers” | No. The nucleosome test found 19% of mast cell tumours. |
| “The validation studies are independent” | No. Both were funded by, or involved employees of, the tests’ developers. |
Sources
- 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: diagnostic validation study. Funded by the test’s developer
- Wilson-Robles HM, Bygott T, Kelly TK, et al. Evaluation of plasma nucleosome concentrations in dogs with a variety of common cancers and in healthy dogs. BMC Vet Res 2022: diagnostic study, 528 dogs with cancer. Several authors employed by the test’s developer
- Flory A, Ruiz-Perez CA, Clavere-Graciette AG, et al. Clinical validation of a blood-based liquid biopsy test integrating cell-free DNA quantification and next-generation sequencing for cancer screening in dogs. J Am Vet Med Assoc 2024. ⚠️ abstract read. Retrospective validation, 1,947 dogs
Always confirm with your vet before acting on anything on this page.