Diagnosing Cancer in Pets - A Case Study
In the previous two articles, What Separates One Type of Cancer From Another? and How to Tell the Difference Between Lymphoma and Leukemia in Pets, I described the challenges faced when distinguishing between lymphoma and acute leukemia in companion animals and the various diagnostic tests I typically recommend in order to distinguish one disease process from the other.
In today's post, I wanted to introduce you to a dog named Pepper, whose story exemplifies the typical complications to a straightforward diagnosis, as well as how best to approach financial restrictions which limit available diagnostic options, and the difficulties owners face when choosing therapeutic options for their pets.
Pepper is a handsome, “big boned,” mixed breed dog weighing in at an impressive 130 lbs. Pepper came to see me a few weeks ago because his primary veterinarian was worried he could have lymphoma.
About three weeks before I met him, Pepper’s owner noted that he was slowing down during his walks and he preferred sleeping in rather than waking up at 5 a.m. as he typically would. He also noted Pepper took longer to finish his meals, and even turned his nose up at treats once or twice.
Pepper’s initial evaluation by his primary veterinarian showed mild enlargement of his external lymph nodes and a 7-pound weight loss since his previous checkup five months ago. Lab work was performed, which showed his white blood cell count was elevated. The breakdown of the count showed an increased number of lymphocytes, and this was confirmed when a pathologist examined a blood smear. Pepper’s vet then referred his owner to see me for further diagnostic and treatment options.
I reviewed Pepper’s previous medical records and performed an exam. I paused when I considered his lab work, knowing that although initial results suggested an increased lymphocyte count, Pepper’s signs were not 100 percent specific for a diagnosis of lymphoma. My intuition told me to stop and consider the possibility of an alternative cause of his signs.
A difficult conversation ensued with Pepper’s owner about my concerns: Though lymphoma occurs more frequently than leukemia and he was referred to see me for a specific diagnosis, my experience and specialization led me to believe Pepper had acute leukemia rather than lymphoma. We spent a great deal of time discussing why it was important to know exactly what was causing Pepper’s signs in order to formulate an accurate treatment plan.
I recommended multiple tests to help support my concern; however, performing all of the tests was not a financial possibility for Pepper’s owner. This meant I would have to pick and choose the tests I thought would provide the most “bang for the buck.”
My top diagnostic test was a bone marrow aspirate. In order to provide the pathologists with the most amount of information possible, I also submitted aspirates from Pepper’s lymph nodes for cytology as well as blood for a complete blood count and evaluation of blood smears.
Bone marrow results returned showing about 25 percent of this tissue was comprised of cancerous blast cells, and identical blast cells were seen in small numbers in the blood smears and lymph node samples as well.
The clinical pathologists who examined Pepper’s samples were leaning towards a diagnosis of lymphoma, however, as discussed previously, the morphology of blast cells is insufficient for distinguishing lymphoma from leukemia, therefore cytochemistry stains were applied to the bone marrow slides.
Twenty-four hours later, the results returned, confirming my suspicions. The cells were negative for the lymphoid markers and positive for the non-lymphoid markers, indicating Pepper had acute myeloid leukemia.
This form of acute leukemia arises from a precursor cell within the bone marrow that gives rise to monocytes. Monocytes are a type of white blood cell, but are different from lymphocytes.
This form of leukemia is considered the most aggressive type we see. Though there is no one universally accepted treatment protocol for acute myeloid leukemia, most veterinary oncologists recommend treating it differently from lymphoma or acute lymphoid leukemia. Had we not performed the additional testing, Pepper would have been treated for the wrong disease and would have little chance of remission.
With a definitive diagnosis in hand, I recommended a specific chemotherapy protocol tailored to Pepper’s exact diagnosis. In this treatment plan, treatments are administered every week for four weeks and then extended to every other week for an additional four weeks of treatment.
Pepper started on treatment and is currently doing great at home. His white blood cell count has normalized and he is back to his typical energy level and his appetite has returned in full force. Though his overall prognosis still remains quite guarded, I’m very happy with his progress thus far.
I realize how complex this topic is, and my goal in writing this series of articles is to introduce people to some of the challenges veterinary oncologists face and why we may recommend additional tests even when a diagnosis was already obtained.
Cases such as Pepper’s represent why consultation with a veterinary oncologist is so important, even when circumstances seem incredibly obvious. Veterinary oncologists have the experience and specialized training to know when a case is not so straightforward, and they know the best way to sort through and interpret this complicated web of tests.
Keep in mind that consulting with a specialist doesn’t mean you are obligated to follow up with expensive tests or treatment plans — you are simply there to determine your options. And you may be surprised to find out we have just as much to learn from your pet as you do from us.
Dr. Joanne Intile