I recently received a request to talk about a specific topic — newly available blood tests for cancer in pets. I didn’t know very much about the subject, but looking into it was fascinating. Here’s what I found.

Blood tests that look for the presence of biomarkers (i.e., something that indicates the presence of disease) associated with certain types of cancer are now commercially available. Two companies offer these tests, and they take somewhat different approaches. One measures the blood levels of tyrosine kinase, an enzyme that can mutate and cause unregulated cell growth, which is the hallmark of cancer. This test can be used to look for lymphoma in dogs and cats and hemangiosarcoma in dogs. The other type of test looks at a how certain proteins are expressed in a blood sample (i.e., proteomic biomarkers) and can be used to evaluate dogs for lymphoma. While the two types of tests are different, they have many of the same pros and cons, so I’ll address them together.

First of all, these tests are not really "cancer screens." They cannot tell you whether or not your dog or cat has cancer or is cancer-free. They only evaluate for the specific cancers, lymphoma and/or hemangiosarcoma.

Also, calling them a "screening test" might make them seem a bit more powerful than they really are. According to the National Cancer Institute, screening is "checking for disease when there are no symptoms," but the companies that make these tests freely admit that they should be used primarily when there is already a high level of suspicion that a pet has the disease in question.

For example, a dog presents with blood in its abdomen and a mass on its spleen. The tyrosine kinase blood test might be useful in determining whether the patient has a hemangiosarcoma versus a hematoma or other benign mass. Another scenario where testing might be useful is in differentiating between inflammatory bowel disease and intestinal lymphoma without the need for intestinal biopsies, either via surgery or endoscopy.

I would not recommend these tests to my clients who have pets without clinical signs associated with lymphoma or hemangiosarcoma. Why? The blood tests have a relatively high rate of false positive results, which means that a large number of clients will be told that their pets might have cancer when they really do not. This will bring about a lot of unnecessary worry and will necessitate additional, expensive diagnostic testing before coming to a definitive diagnosis of "no cancer."

So as I see it, these blood tests for lymphoma and hemangiosarcoma could be beneficial in very specific situations, but they are not true "cancer screening tests." Keep in mind also that they have not been widely used and therefore may have some glitches that we are not yet aware of. The results should be looked at as just one more piece of information that must be analyzed in combination with a pet’s history, physical exam, and the findings of more established diagnostic tests.

If anybody else has a topic they’d like to learn more about, pass it on and I’ll see what I can do.

Dr. Jennifer Coates

Image: From Dogswalk Against Cancer; IMG_2084 by Adam Scally / via Flickr