In an ongoing series on how different kinds of cases are worked up, today we will look at veterinary oncology (cancer) patients.
Very likely the scariest word in the English language after Hell.
Or, maybe they even have a relationship to each other.
Of course, cancers range from curable to deadly-overnight, whether in dogs, cats or people.
Most patients that present as oncologic cases have a visible growth or mass. Such cases are approached differently from cases that present ill and later testing reveals they are ill because of cancer. We’ll look at the former scenario first.
Interestingly, visible masses in dogs and cats are rarely diagnosed by visible traits alone. This differs from people’s cancerous external growths, which usually give strong visual cues even before a biopsy is taken. (Click here to see May 4, 2007, Daily Post about Dr. Randolph’s Pathology class experience on this topic.)
So, our first steps involve trying to get microscopic clues from a mass.
This process often begins with a fine needle aspirate (FNA). The technique involves using a tiny needle on a relatively large syringe, inserting the needle into the mass and “aspirating” or pulling back on the syringe plunger in an attempt to pull fluid and identifiable cells into the needle. The needle’s contents are then squirted onto a microscope slide which is then sent to a board-certified veterinary pathologist.
When the pathologist’s office receives the slide they will treat it with fixes and stains, exposing the identities of the various components.
If the FNA was successful, a diagnosis and possibly a prognosis are given and your pet’s doctor may begin treatment.
Sometimes, though, growths don’t give up cells to FNA. Fibrous growths are the worst offenders, in which case we usually get a note from the pathologist advising us to obtain and submit a tissue sample or biopsy.
While FNA may be performed with the patient awake or under light sedation, biopsy is usually performed under full general anesthesia.
After tissue is removed surgically it is fixed (preserved, usually in formalin, a mixture of formaldehyde, water and buffers) before submitting it to the pathologist. A variety of different tissue-staining techniques may be used to force the sample to disclose its true identity to the doctor.
Once a final diagnosis is reached, the decision is made to treat the mass with surgery, radiation, chemotherapy or a combination of modalities.
The second scenario, in which the patient’s cancer is not externally visible, the diagnostic approach is often radically different.
For example, leukemias, cancers of the white blood cells are occurring invisibly as well as microscopically in the bloodstream. A pathologist’s review of a routine test called CBC or Complete Blood Count may be required to characterize the exact nature of the leukemia.
In other cases a mass may be palpable (felt) in the chest or abdomen and need further investigation. Radiographs (X-rays) of the body part, along with ultrasound images may help the clinician come closer to a diagnosis. Ultrasound may also be used to obtain a sample of the mass by watching a biopsy device be advanced from the outside of the body into the mass. When the clinician sees that the device is in the right place he activates the device, then removes it along with the biopsy specimen.
Some internal masses don’t lend themselves to being biopsied from the outside and surgery is required to obtain a biopsy with laparoscopic or open-cavity technique.
As with external masses, once a diagnosis is obtained, treatment is begun according to cell type and patient factors.
In summary, cancer in pets is about as common as it is in people. A variety of techniques may be used to obtain a specimen, after which a specimen is transferred to a pathologist for diagnosis. Pathologists have many tools at their disposal for fine-tuning a diagnosis. Accuracy of the diagnosis is crucial for a good response to treatment.
Just as in human medicine, veterinarians rely on the expertise of our pathologists to be able to successfully treat our dog and cat cancer patients.