Is the Early Cancer Detection Blood Test Worthwhile?

OncoK9 recommends screening for giant and high-risk breeds at younger ages.
OncoK9’s recommended ages to start cancer screening

If you’ve been in a vet office lately, you might have seen a brochure advertising the OncoK9 blood test, an early-detection cancer screening test.

I first heard of it when I took Cali to a specialist who ended up diagnosing her hemangiosarcoma. By then, we had done the ultrasounds and were on our way to the splenectomy, so I didn’t “need” the test; I knew she had cancer.

The blood test “uses a simple blood draw to detect abnormal DNA released into circulation by cancer cells,” and claims to be able to pick up on these markers before the dog would be likely to have any symptoms. Dogs with some cancers, like hemangiosarcoma, rarely show any symptoms. OncoK9 is said to be able to detect 30 different types of cancer, including several very common canine cancers.

The company recommends it annually for dogs aged 7 and older, with different guidelines for cancer-prone breeds. They suggest starting screening at age 6 for goldens, for example, and age 4 for boxers (see illustration above).

Should you do it?

I can’t answer that, but I can share the pros and cons I see.

An argument for doing the test is that early detection gives you the best chance to treat some cancers.

Now for the “cons.” The test detects cancer markers, or claims to, but it does not give any indication of the type or location of the cancer.

A friend who works for a vet in another state reports that her clinic looked into the test, and her vet worries about the high potential for false negatives — not catching the presence of cancer markers — as well as the smaller, but still present, chance of false positives. Paired with the lack of indication of what type of cancer the dog has, a false positive could send a family on a very costly, stressful wild goose chase to try to identify the nonexistent cancer.

This vet says the test “might be helpful” for a dog with unexplained weight loss and no other evidence of disease; that’s far from a blanket recommendation for an annual check!

Finally, the cost: The test costs $500 at my specialty clinic. Cost will vary by location, but it’s not an inexpensive test. A few hundred dollars (or more) is a hefty addition to your dog’s annual checkup, and it’s unlikely that pet insurance would cover it.

My specialist vet’s office told me that, following a positive test, the next steps would be tests to figure out the type and stage of the cancer. And that anyone with a positive test gets a $1,000 credit toward that testing. I assume that this is because the company that does the OncoK9 test uses the follow-up and test data to refine the test and/or to work on treatments. Either way, the hefty sum tells me that a) the follow-up testing is pricey and b) they don’t expect a huge proportion of positives.

What do you DO with a positive result?

That raises the next obvious question, which is: If I were to get a positive test result, what would I do?

  • If you are not prepared to go down the expensive route of testing to identify and stage the cancer, then treat it … I’m not sure what you gain by doing the test.
  • If you are, and you have a dog of a breed that is likely to get cancer, then early detection and treatment could give you more time with your dog and/or lead you to an early treatment that spares your dog some suffering, depending of course on what additional testing you did, how quickly you identified the dog’s cancer, and whether it was a treatable cancer — all significant questions.

Whether to do the test (and what to do afterward) is, of course is a very individual decision.

Orly is only 1. I am certainly hoping that we have more reliable, less costly ways to detect (early) and effectively treat canine cancer before she’s of an age where I’d face the question of whether to do this type of test. Cali spent her life helping to make that happen; and the many researchers working on canine cancer detection and treatment offer hope for future pups.

Are Mixed-Breed Dogs Healthier?

A mixed breed dog relaxes with a Labrador and a golden retriever on a sofa.
Who’s healthier?

A recent blog post by Dr. Stanley Coren mused about “hybrid vigor” or the notion that mixed-breed dogs are healthier — or, at least, less prone to genetic diseases — than purebred dogs. I decided to read the full study he referenced to learn more.

A large group of researchers, mostly Finnish, studied a huge sample of dogs: more than 83,000 mixed-breed and more than 18,000 purebred dogs of 330 different breeds. They analyzed the dogs’ genotypes, looking for 152 different genetic markers that underlie hereditary diseases.

They quickly narrowed down the study: Of the dogs with a faulty gene, 96 percent had one (or more) of a group of 30 genetic markers or “disease alleles.” They narrowed further, selecting the nine most common markers, which all appeared in multiple purebred breeds as well as in mixed-breed dogs in the sample.

Several findings might be interesting to dog owners:

  • Mixed-breed dogs are as likely or more likely to carry some genetic variations linked to diseases than purebred dogs.
  • But purebred dogs are more than twice as likely to actually have a genetic disease.
    That makes sense; the number of purebred dogs who are actually bred is quite small, and many are bred to dogs from the “same lines” — relatives, even very close relatives. Within a closely related population, the likelihood of dogs sharing a recessive gene is much higher than in the broad population of mixed-breed dogs.
  • Deeper study of individual mixed-breed dogs who carried rare genetic variations found that, even when the dogs exhibited symptoms of a genetic disease, these individual dogs were only diagnosed after the owners had the results of the genotyping.
    That also (sadly) makes sense: The vets didn’t suspect that the mixed-breed dogs had rare, usually breed-linked, genetic diseases.

The question of “hybrid vigor” is nuanced, since the dogs are likely to be carriers but less likely to suffer the diseases, but I’d argue that mixed-breeds are healthier.

In his post, Coren also points out that another common belief — that breeders frequently breed dogs known to be carriers or even sufferers of a disease — is unfounded. Many breed-specific genetic diseases have become extremely rare or have been eradicated — due to careful breeding. Some breed clubs forbid breeding of carriers of known genetic diseases.

The researchers are sharing their data; they’ve created the free My Breed Data database, where anyone can search for information on genetically linked diseases.