The Importance of Pathology in Veterinary Oncology

So, how do we as veterinarians and you as a pet owner know whether or not to worry about that lump on your pet?

Once in a great while an oncologist or very experienced general practitioner might be able to give a strong indication of whether a lump is something to worry about, and even what it might be, based just on a physical exam. But the huge majority of the time the decision requires pathology. Yes, veterinarians are special but even our eyes and our fingers are not microscopes!

And, “if it’s worth taking off, it’s worth sending in” (that means, if you are having a lump surgically removed from your pet there is rarely a reason not to have the veterinarian send it in for pathology – if you’re absolutely certain it’s benign then why are you having it removed?

As oncologists seeing pets with cancer on referral, admittedly we only hear about the times it goes wrong and not about the many times that nothing bad eventuated. But, many is the time that we’ve wished for a time machine to diagnose a cancer that first showed signs weeks, months or even years ago.

Being able to obtain diagnostic samples and establish a definitive diagnosis is crucial to formulating a prognosis and developing an effective treatment plan for any pet with cancer and it is a big part of what veterinarians and veterinary oncologists do. This is really square one.

Moreover, we may not even be happy with just sending a sample in to a pathology laboratory. We might even be picky about which lab and which pathologist; because just as a veterinary practitioner might be more interested in one type of problem than another (for example, reproduction or dermatology); not all pathologists are equally focused on oncology – some might be more interested in dermatology, or bone pathology, or infectious disease. Therefore, for a veterinary oncologist, identifying veterinary pathologists that excel in oncologic pathology is a major priority when developing an animal cancer treatment team.

As oncologists, we don’t just read the diagnosis line either, we read the whole description because there’s often additional information in there that may be helpful. We’re interested in more than just “Is it cancer or not?” but also the tumour type, and in many cases the “grade”, and other characteristics like the “surgical margins” and “mitotic index”. Depending on the individual case, all these may factor into the prognosis for the patient and a plan of how best to approach this cancer.

But wait, there’s more! We almost always want to know other things too, because another old motto is “treat the patient, not the tumour” – so we also need to know all about their overall health aside from the cancer. This also feeds into the overall prognosis and treatment plan. This means that the veterinarian needs to run “general health panels” – blood and urine tests that look at the whole pet, not just the cancer.

In the diagnostic process, we might suggest cytopathology (or cytology) (usually the sample is a “fine needle aspirate”) and / or histopathology (usually the sample is a “biopsy”). These are often read by two different pathologists – again, they have their areas of expertise too. In some cases veterinarians might suggest going straight to histopathology, as this is usually needed to provide all the information we need to make a final plan. But in some cases we might suggest starting with cytology and then proceeding to histopathology depending on the results. The pros and cons of these two types of pathology, and when to use which one, depend on the individual case.

Sometimes even histopathology doesn’t give us all the information we want about a pet with cancer, and we need to request additional tests to be run on the sample, including various types of special stains and subtyping tests. We only recommend these tests if the information to be gained will be helpful to the pet. Sometimes if the pathologist is having difficulty classifying a particular tumour and special stains or other tests are needed, this can take more time and it can become frustrating for a pet owner. But, as much as we wish that pathology were an exact science, it isn’t. There is subjectivity in it and even the very best pathologist can’t always make a final diagnosis “just by looking”. In fact, in our experience, the best pathologists are the most likely to offer additional tests because they are the ones who are most aware of the subtlety and subjectivity of their discipline, and also the most aware of the usefulness of the extra information that can be gained from these tests and take the trouble to make them available.

Although on this website we tend to focus on the implications of a cancer that is missed; there is another side to this coin. That is, what if we assume that a lump IS cancer when it actually isn’t. In veterinary medicine, that can be equally life-threatening because if a pet owner is mistakenly given a grave prognosis then they may choose to have their pet euthanized when it wasn’t really necessary. Or, they may just miss having the correct condition appropriately treated. Here are a few examples:

Brodie is a bouncy and loving 10 year old desexed male Staffy. He came to see his veterinary oncologist with multiple lumps in and under his skin. He had been treated a year earlier for a mast cell tumour, so when he came in with multiple lumps the obvious fear was that his mast cell disease had disseminated. Based on this assumption, his prognosis would be considered grave and many pet owners would have chosen euthanasia for him at that time. Luckily for Brodie though, his dedicated owner agreed to have histopathology done on the lumps. Guess what, not only were they not mast cell tumour but they weren’t cancer at all – they were a rare infectious disease called canine leproid granulomatosis, and he was cured with a course of the correct antibiotic.

Every cat owner fears oral squamous cell carcinoma. This is one of the most relentless cancers of older kitties and erodes quality of life very quickly. A typical presentation is of a proliferative and erosive lesion under the tongue in an older cat, and certainly a lesion of this appearance in an older cat is extremely worrying. So when beloved 12-year old China presented with a history of drooling and halitosis and a peek under the tongue disclosed the dreaded lesion, it was most fortunate that her veterinarian performed a biopsy and made a diagnosis of eosinophilic granuloma. Had a diagnosis been made based only on the appearance she would have been either treated incorrectly or euthanized needlessly.

When your veterinarian suggests what seems like a lot of tests for your pet in the process of diagnosing or staging a possible cancer, it is important that you understand what each test entails and the reasons for it. But do remember that the more we know about your pet the better we can help.