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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Cancer Blood Testing in Future for Pets?

Updated: June 18th, 2019

A new test is being developed in human medicine which allows for breast and a type of lung cancer testing with a blood sample.

This exciting development may be a sentinel for testing in pets that is so needed.  Dog cancer is now the number one killer of dogs in the US, and early intervention is therefore becoming more and more important.

One of the reasons this is an essential post for dog guardians is not that the test being developed will be used for dogs right now.  More importantly, it is because there is a common misconception that one can test for cancer in a dog using a blood test.

I have heard many times the phrase, “The blood work was fine” from people first becoming familiar with dog cancer.  Although this is a bit reassuring, when we are dealing with malignant cancers it really is just barely reassuring… to someone in my position at least.

Let me explain.

First of all, one cannot diagnose cancer (except possibly some leukemias) with a blood test. So a normal result does not rule out cancer or mean that we don’t have spread.

Second, folks need to understand that these blood tests we have are very coarse measuring instruments. Take the kidney markers, as one example. These markers will not go up until 2/3 of the kidney tissue is not working normally. That’s a huge amount! So we can literally have half the kidney volume not working in a dog and have normal kidney markers.  Other testing gives us more accurate and complete information.

Third, we need to understand that there is an issue called micrometastasis, which you can learn more about here.

The best way to tell if there are cancer cells in an area is to sample the area and send the sample to a pathology lab.  The pathologist will send a report on the sample which will describe whether it contains cancer cells or not.

There are different types of samples that can be submitted. A biopsy is a piece of the tissue (or the whole lump, for that matter).  Sometimes a fine needle aspirate is used to collect cells, which is where a needle is used to suck out cells for submission to the lab. Sometimes other body fluids can be used that are collected from body cavities or organs too.

There is a commercial veterinary test for lymphoma that can be used on the blood, yet the manufacturers caution against relying on the test results to rule in or rule out the disease definitively. There is also a urine test that can be used for bladder cancer, although the interpretation can be tricky (if it’s negative, there is likely no cancer. If it’s positive, we don’t know).

So, we are left in some cases with a rather unhappy situation that I describe as an “information deficiency state”.  This is a fancy way of saying we sometimes have to guess as to the best possible medical step in the absence of cold, hard facts.  In these cases, we rely on experience, judgment, and treatment plan analysis…and intuition.

If you would like more information, check out the Guide.


Dr D




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  1. Joan on November 14, 2012 at 3:20 pm

    My 8-year old Bouvier (now 9) was diagnosed with osteosarcoma in late June. We followed the gold standard for treatment: amputation (rear leg) and 4 rounds of carboplatin. I have the book and the APOCAPS. I really appreciate this website and refer back to it numerous.
    I tried to get her into the U of PA trial for a bone cancer vaccine. She has the Her-2/neu antigen in her tumor which qualified her for the trial but also means her bone cancer is extra aggressive. Unfortunately, her immune system failed to respond when tested and the vaccine would not be effective for her. Within a month of the last chemo she had tumors in both lungs (which were clear prior to amputation. Three weeks ago, I received a prognosis of 1 month maybe two.
    Up until 3 days ago she was doing well. Coughing but had a good quality of life, ¾ mile jog 3-4 times a week, and underfoot in the kitchen the minute the refrigerator or cabinet door opened. Then she slowed down 2 days ago. Could barely trot after a rabbit. She has put on ~5 pounds since the amputation and I started cutting back on food trying to get weight down.
    Now she has a fever ( 103.4-104) and no appetite, and not coughing as much. Vet can’t hear any sign of pneumonia in lungs but not conclusive. She’s been placed on Clavamox. Vet was uncertain: Is a fever common with osteosarcoma? Another vet had suggested when she loses her appetite, he would use prednisone to make her feel better in her final day and keep her eating. At this point, I am just concerned with her quality of life. She’s alert, still licks my nose (but not as much), loves sun bathing on sunny days. I just want her to start eating again. What is the best way to support a dog until it is time to part?

  2. Nancy on October 10, 2012 at 8:53 am

    This is really informative as it relates to our 8-year old lab mix who had a fibroblastic sarcoma removed 6 months ago. He was diagnosed at intermediate stage and we were told the bloodwork was “fine” and his lungs (as we were told this is where it might metastasize) were clear.

    He goes back for his post-surgery checkup in a few days, and has had no chemo/rad or symptoms of anything, and thankfully, no new lumps. My question is this: If our vet wants to do bloodwork and/or lung x-rays again, is this really necessary?

    Thank you for your time.

    • Dr. Susan Ettinger on October 23, 2012 at 3:54 pm

      Six months is definitely a reasonable period of time for follow up blood work and chest X-rays, especially considering how quickly dogs age. Good luck!!
      All my best, Dr Sue

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