Blood test for the diagnosis of canine lymphoma: What primary care veterinarians should know

Editor’s note: Since the time of this filming, Craig Clifford, DVM, MS, DACVIM (Oncology) has left BluePearl and is now working at Northstar Vets.

Cancer screening in dogs has long relied on physical examinations, blood work, and imaging, none of which look for a specific cancer. Liquid biopsy, which searches a blood or fluid sample for markers of cancer elsewhere in the body, is starting to change that, and canine lymphoma is among the first cancers it targets.

For the debut episode of Cliff's Edge, dvm360's new oncology podcast for busy primary care clinicians, host Craig A. Clifford, DVM, MS, DACVIM (Oncology), a medical oncologist at BluePearl Pet Hospital in Malvern, Pennsylvania, welcomed Pamela D. Jones, DVM, DACVIM (Oncology), DACVR (Radiation Oncology), a specialist support veterinarian at IDEXX. Jones explained how the IDEXX Cancer Dx test can serve as a wellness screen and help diagnose ill patients, what its sensitivity and specificity mean in practice, how to approach a positive result in a healthy dog, and why choosing an appropriate at-risk population matters.

Below is a partial transcript, edited lightly for clarity.

Craig A. Clifford, DVM, MS, DACVIM (Oncology): If a patient comes in, it's a normal dog, the veterinarian elects to run this, and the test comes up positive, how would you guide that primary care doctor when the exam was completely normal and it truly was a screen?

Pamela D. Jones, DVM, DACVIM (Oncology), DACVR (Radiation Oncology): We looked back at over 11,000 retrospective lab tests, and we're also doing a huge prospective study with more than 5000 patients, where we're looking at using it as a wellness profile. In the first 3000, we found that in cases that come back consistent with lymphoma but are perfectly healthy, if we dig a little deeper, we find lymphoma in more than half of those cases. One particular dog came in for a wellness profile, a 10-year-old dog feeling great, and when these owners got back this consistent with lymphoma in this perfectly healthy dog, they said, “Sure, let's dig deeper.” We did deeper testing on the lymph nodes, normal lymph nodes, and we found subclinical disease, so earlier-stage disease. So now what we recommend, based on those preliminary results, is if you have an owner that's very proactive and wants to delve deeper, that's the time to dig deeper. Conversely, you may have an owner that says, “I want to be a little more conservative.” Maybe their dog is older. Maybe they haven't had a good experience in the past with cancer. That's the time to have that discussion: Let's tell you what to watch for at home, like lethargy, loss of appetite, change in behavior. Look for where lymph nodes would be. If that pet has those signs develop, then let's get them back for another physical exam.

Clifford: What do you think is the biggest mistake clinicians might be making with it currently?

Jones: In wellness, use it in an appropriate screening population. When you are doing any type of cancer screening, you want an appropriate at-risk population. If you don't have an appropriate at-risk population, you're going to drive those false positives higher. The best example I always think of is men. In the human population, we know men get breast cancer, but we also know the prevalence in men is so extremely low that that's why we don't use mammograms to screen men. If we used mammograms to screen all men, then we would come up with a lot of unnecessary diagnostics, maybe even overdiagnosis and overtreatment, and we don't want that for our pets. General practitioners often say, “We all know golden retrievers get tons of cancer, and lymphoma especially. Why don't we start testing golden retrievers at 6 months of age?” I've treated goldens with lymphoma at under a year of age. However, the prevalence is a low that if we tested all golden retrievers at 6 months, we would get a high number of false positives, and we would definitely overdiagnose, overtreat, and do too much unnecessary testing.

Want to hear the rest of the conversation? You can listen here or wherever you listen to podcasts