What is my pet’s cancer stage? What does that even mean anyway?

Veterinary oncology is raft with confusing terminology. We toss around intricate multi-syllable words such as metronomic chemotherapy, radiosensitizer, and remission with little regard for their complexity of definition. I constantly need to remind myself to remember to simplify the language and take the time to explain the details thoroughly.


As an example, owners will often ask me what stage of disease their pet has at the onset of their diagnosis, when all we know at that point is they have a tumor that was previously biopsied or aspirated to be cancerous. When this happens, I have to remember to pause and take the time to define the term “stage” carefully so they can truly understand the question they are asking.


Stage refers to where in the body we find evidence of cancer. In veterinary medicine, we model our staging schemes off of those available for humans.  The World Health Organization (WHO) is the institution that establishes the “rules” for staging disease for people with cancer. Veterinary medicine lacks a similar governing body, however we use the paradigms established by the WHO and modify them for our needs.


We have accurate staging schemes for many of the common cancers occurring in primarily dogs and a few of the more common cancers in cats. Beyond that, we often lack information regarding stage, and for many cases the term simply does not apply to the case.


The most important aspect to consider for veterinary patients with regard to stage of disease is that to accurately assign a stage to their case, the pet would need to undergo all of the essential diagnostic tests required to provide the information.


The best example would be lymphoma in dogs. The modified WHO staging scheme for this disease is as follows:


1 Single lymph node on one side of the diaphragm
2 Multiple lymph nodes on one side of the diaphragm
3 Multiple lymph nodes on both sides of the diaphragm
4 Liver and/or spleen involvement (+/- any lymph node involvement)
5 Extra nodal involvement (e.g. bone marrow, peripheral blood, skin, eyes, etc.)



In order to truly know what stage a dog with lymphoma would be, we would need to do the following diagnostics: Physical exam, complete blood count with pathology review, chemistry panel, urinalysis, lymph node biopsy, three view thoracic radiographs or thoracic CT scan, abdominal ultrasound or abdominal CT scan with sampling of the liver and spleen, and bone marrow aspirate.


These diagnostics range in terms of invasiveness, ease of performance, availability, and cost. For the average canine patient with lymphoma, the results of these tests would ultimately also not change our recommended treatment plan and could wind up costing thousands of dollars that would better be spent on battling their disease.
Therefore, in most cases, we find ourselves “picking and choosing” the diagnostic tests we need to have performed in order to best assess that particular patient’s disease status and to provide reasonable expectations as to prognosis, while maintaining resources for treatment.


Though I recommend full staging for all patients with lymphoma, I can recognize this may not be an option for all owners. For some cases we will move forward with treatment based solely on lab work and some sort of test on an enlarged lymph node whereas for others I will more strongly urge for biopsy or imaging tests or a bone marrow aspirate. In an ideal world we would have all the available information we could about our patients, but in reality, this just isn’t possible.


Some studies show the higher the stage of disease, the poorer the outcome for dogs with lymphoma, however my clinical experience starkly contrasts such information. To me, it’s not how “widespread” the disease is in the patient’s body, but rather how they are feeling at the time of diagnosis and whether we see it in specific anatomical areas or not.


For other tumors types, performing staging tests to examine for spread of cancer is often very important as it will dictate my treatment recommendations and will allow me to better determine a patient’s chance of response to treatment.   For owners, knowing how advanced their pet’s disease is at the time of diagnosis allows them to make decisions about their care and to be realistic about their outcome.


What can be most surprising is that in some cases, stage simply doesn’t seem to make a difference at all.   A dog with a very large brain tumor may theoretically have stage 1 disease, but may have a very guarded prognosis due to the size and inoperability of the their tumor. A dog with stage 5 lymphoma may have a prognosis of  1 or more years with treatment.


I’m not one to become hung up on terminology or numbers, so I try to focus on the individual characteristics of the animal I am treating. Yes, stage matters, but what matters more is how the pet is feeling and what realistic options we have for them.


The tests are important, but what is more important is the actual patient. That’s often the only stage that truly matters in the end.





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