What is liquid biopsy for lymphoma and who should get it?

Pamela D. Jones, DVM, DACVIM (Oncology), explains how IDEXX Cancer Dx works as a blood test to screen for lymphoma. She discusses why screening is most useful when applied to appropriate risk groups, such as older dogs and breed predisposed dogs, to minimize false positives and unnecessary interventions.

Transcript

Pamela D. Jones, DVM, DACVIM (Oncology): CancerDx is truly a liquid biopsy test. It is a blood test and right now it is used to screen for lymphoma. We can also use it as an aid in diagnosis for sick dogs. When I think about cancer screening, I compare it to human screening tests such as mammograms for breast cancer, colonoscopy for colorectal cancer, and Pap smears for cervical cancer. Those tests are very specific.

What most of us want is a blood test that can be included in a routine wellness profile at the primary care visit to look for signals of cancer. Pet owners ask for that all the time. I wish I had a dollar for every time a pet owner asked me, "Can you just do a blood test and tell me if my dog has cancer?" Veterinarians hear that every day and that is what research is trying to achieve.

The advantage of CancerDx through IDEXX is that it is a simple blood test that can be submitted easily. It is also affordable. Talk to your IDEXX representative about pricing for your practice. As a screening test the most important part is using it in the appropriate population. That means the risk population, meaning older dogs. A good study shows the median age for dogs to develop cancer is 8.8 years. We recommend beginning screening at 7 years of age.

There are also at-risk breeds such as boxers, German Shepherd Dogs, and golden retrievers. Numerous studies show these breeds develop cancer sooner and for them we recommend starting screening at 4 years of age. You might ask, why not screen a six-month-old golden retriever? The reason is that the risk is not high enough in very young dogs and screening them would raise the false positive rate.

The best way to think about this is what we have learned in humans. We do not do breast cancer screening in men because they are not an appropriate high-risk population for mammography. We do not start colonoscopies at age 20 because the risk is too low. Being judicious about who we screen keeps false positives as low as possible.

That is a tough concept because people think if it is a screening test why not run it on everyone. The issue is false positives. We must keep false positives as low as we can, so we do not create unnecessary fear or overdiagnosis from a cancer screening positive result.

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