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The veterinarian says your dog has cancer, so already you’re beside yourself. But you know you need to take a breath, because some cancers have better prognoses (odds of a good outcome) than others. A couple of the ways doctors determine how treatable the cancer may be are to grade it and stage it. But what do those words mean?
Grading
The “grade” a cancer receives tells what it looks like under a microscope. A sample of malignant cells might be obtained via biopsy before surgery or taken from the cancerous mass once some or all of the tumor has been removed. A veterinary pathologist then takes into consideration various characteristics of the cells that can’t be seen with the naked eye in order to assign a grade.
Generally speaking, says Tufts veterinary surgeon John Berg, DVM, a low grade (like I) is a good thing, prognostically speaking. It means the cancerous cells look pretty much like normal cells. A high grade (like III) is not as promising. Not only will the cells look markedly different from normal cells, they will probably be reproducing more rapidly.
Staging
Staging looks at such issues as how big the tumor is, whether it is invading local tissue, and whether it has metastasized (spread) to distant sites. To get at this information, veterinarians rely on a number of screenings. These include a physical exam, ultrasound, radiographs (x-rays), or advanced imaging like a CT scan or magnetic resonance imaging (MRI). Large tumors, tumors that have invaded local tissue, and tumors that have spread to distant sites generally have a worse prognosis than tumors that do not have those characteristics.
“Stage is highly predictive of outcome for most cancers,” Dr. Berg says. A dog with stage I cancer generally has a better chance of getting through it than a dog with a higher stage.
But both grading and staging are essential parts of arriving at a likely prognosis, he says, and provide the information a veterinarian needs to help the owner make treatment decisions. For instance, if a cancer is both grade I and stage I, chemotherapy once the tumor has been surgically removed may not be necessary.
