Staging and grading cancer in dogs takes some time but is very helpful. This process tells us how far cancer has spread and how aggressively it will likely behave. This helps determine a dog’s prognosis and treatment plan.
- Staging refers to how large a tumor is and how far in the body it has spread. This is different than grade, which describes the behavior of a cancer and how aggressive it is. How aggressive a cancer is can give insight into how likely it is to spread.
- The higher the stage, the more a cancer has spread to other places in the body. Stage refers to how large the tumor is and how far it has spread from its original location.
- Stage 5 cancer in a dog typically is used in lymphoma staging and is the last stage. It indicates that the bone marrow or other organ system is impacted. This is the last stage of the disease.
- Stage 4 cancer in dogs can refer to multiple different cancers. For lymphoma, it refers to the second to last stage and indicates that the liver and/or spleen are involved. For mast cell tumors, Stage 4 is the last stage and indicates distant metastasis.
- Tumor grading in dogs requires microscopic evaluation of the cancer cells and is most accurately done on larger samples of tumor tissue like whole tumors or biopsies. These larger samples are cut into thin, small pieces to be evaluated under a microscope. Specific measurements will tell a pathologist how aggressive the cancer is.
Staging and Grading: Important for Understanding and Planning
Unfortunately, knowing your dog has cancer isn’t usually enough to make a treatment plan. Staging and grading cancer in dogs is the next step. Once you have the information gained from staging and grading, your veterinarian or veterinary oncologist can offer you treatment options.
Dog Cancer Staging
Cancer staging is a way of determining the extent to which cancer has progressed. The higher the stage number, the more progressed the cancer is, and often the worse the prognosis is as well.
Staging is based on how large the original tumor is and/or where the cancer cells have spread in the body (metastasis).
Knowing where the cancer is and how much is there gives the information used to estimate prognosis (the likely course of the disease), lifespan, and quality of life.
This information is also used to make decisions regarding what treatments will be best for your dog.
How Veterinarians Determine the Stage of Dog Cancer
There are many tests used in the staging process. These tests include:
- Physical exam
- Blood work
- Imaging (x-rays, ultrasound, CT, or MRI)
- Biopsy of tissue areas near the original cancer site
This information is used to determine the extent of the original tumor, which lymph nodes it has spread to, and the extent of spread to distant tissues or organs.
The staging process differs depending on the cancer type.
- Cancers that affect the blood or bone marrow such as lymphoma can have different staging systems than tumors or individual masses.
- Other cancers of the blood, such as leukemia, may not have a specific staging system.
- Brain and spinal cord cancers also have specific staging systems that are determined by their cell type and grade of cancer.1
Let’s look more closely at the types of tests used to stage cancer in dogs.
The physical exam is the first critical element of staging. Your veterinarian will measure the tumor if it is external and visible, feel lymph nodes to determine their size and possible involvement, and examine and feel the abdomen for any related abnormalities. Your vet will also listen to the heart and lungs to check for anything unusual.
Imaging is an essential component of staging cancer. Imaging methods make it possible to look inside the body for evidence of cancer. With this technology, specific types of pictures or videos can be taken.
While the physical exam can evaluate some elements of internal structure through feel and sound, methods such as x-ray, ultrasound, CT scan, MRI, and PET scans allow doctors to visualize the inside of the body. These methods help the vet figure out where the cancer is and how much is there.
Biopsies and Pathology Reports
Pathology reports are written descriptions of samples of cancer. They can tell us the size of a tumor, the cancer cell type, and how aggressive it is.
Pathologists are specialists who use a microscope to look at cell details of a sample of your dog’s tumor. The pathologist records everything they see and write it up in a report for you and your veterinarian(s).
These reports may be made after the pathologist evaluates a piece of affected tissue (biopsy), a whole tumor after removal, or a small sample of cells on a slide (cytology).
Surgical reports and pathology reports performed after the removal of affected tissue can also provide information on the tumor size, appearance, lymph node involvement, and if the whole tumor was removed or some cells were left behind.
Bloodwork and Other Testing
Laboratory reports such as blood work, urinalysis, and specific tissue testing can be helpful. Blood tests and urinalysis give a good overview of your dog’s health.
Values on blood work relating to the kidneys, liver, and some parts of the gastrointestinal tract can sometimes give information about whether or not that tissue is affected by cancer.
There are some tests that can be done on organ tissue or fluid that use advanced lab methods to genetically identify certain types of cancer cells. There aren’t tests for every cancer yet, but more options come on the market every day.
What the Cancer Stage Means
Stage refers to how large the tumor is and how far it has spread from its original location. There are multiple specific systems to describe this. In general, if a staging system uses numbers, higher numbers mean more advanced cancer.
One of the most widely used systems of staging is abbreviated TNM.2
- The “T” refers to the primary tumor type, size, and extent.
- The “N” refers to lymph nodes. This describes how many are involved and to what extent.
- The “M” refers to the presence of distant metastasis.
Within this system, there will be additional letters or numbers following the T, M, or N. These give more specific information about the extent of the cancer.2
Your veterinarian will let you know how your dog’s specific cancer is staged. But let’s briefly look at two common cancers and how they are staged.
Since lymphoma is a cancer of white blood cells and does not start as a physical tumor, the TNM system doesn’t really work. Instead, lymphoma has its own staging method. Lymphoma (Lymphosarcoma, LSA) has five main stages depending on extent of disease in the body:3
- Stages I-V are based on how many lymph nodes are enlarged and whether or not they include both halves of the body (front and back).
- Stage IV indicates that the liver and/or spleen are involved.
- Stage V indicates that the bone marrow or another organ system is impacted.
- Each of these stages can have a substage A, which indicates the patient feels well, or a substage B, which indicates that the patient feels ill.
Mast Cell Tumor Staging
Mast cell tumors also have a staging system that is made up of stages 0-4. This system is based on:
- How many tumors are present
- Whether or not there was complete surgical removal
- How many lymph nodes (if any) are involved
- If there is distant metastasis (Stage 4).
- Within Stage 4, there are substages A and B that refer to the presence or absence of signs such as vomiting and diarrhea
Dog Cancer Grading
While stage refers to the extent or spread of cancer, grade refers to the cell qualities of the tumor itself and how likely it is to spread based on this.
The grade is a way of predicting the biological behavior of the cancer.
For example, a higher-grade tumor indicates a more aggressive cancer. As a result of this, the oncologist may recommend a more aggressive treatment plan that involves multiple modes or angles of treatment.
These grades help decide overall prognosis and progression of disease to determine the best planning for treatment and guardian expectations.
How Veterinarians Determine Dog Cancer Grade
Grading requires evaluation of the cancer cells under a microscope. Larger biopsies or a whole tumor are usually the best option for the best accuracy. These large samples are cut into thin, small pieces to be evaluated.
How the cells look will determine the grade of a tumor. The pathologist will look at how similar the cells look to each other, how similar the nuclei (center) of the cells look to each other, how fast the cells appear to be dividing, and how similar the cancer cells look to a normal cell.
Some pathology reports automatically include a grade, but other times your veterinarian will need to specifically request it.
What the Cancer Grade Means
Low-grade tumors generally have a lower risk of regrowing after removal, invading surrounding tissue, and spreading to distant places in the body. They also often have a better prognosis.
Any tumor designated as high-grade typically has a poorer prognosis, shorter survival time, and higher likelihood of spreading.
Different tumor types might have very specific grading systems.
- Mast cell tumors are frequently divided into high-grade and low-grade as a two-tier system.
- Soft tissue sarcomas have a more complex system as do many carcinomas.
- Some people also divide lymphoma into high-grade or low-grade depending on the cell size and type of lymphocyte affected.
When Grade Doesn’t Matter
There are some cancers for which we do not have a good grading system because the specific cell characteristics measured do not actually reflect the cancer’s behavior within the body. In that scenario, the grade is not considered to be useful.
An example of this is squamous cell carcinoma of the digits (toes).4 If your dog has this cancer or another that doesn’t have a validated grading system, your veterinarian will not bother requesting a grade.
Costs Associated with Staging and Grading Cancer in Dogs
Cost of staging and grading varies depending on tumor type and where in the country the process is taking place.
Some general estimates for diagnostics are:
- X-rays: $100-700 depending on how many images are taken and if a boarded radiologist is viewing them. A standard 3-view x-ray study with a review by a boarded radiologist is about $350.
- Physical exam: An exam by a general practice veterinarian ranges from about $50-100. An exam by an oncologist or other specialist ranges between about $150-$250.
- Ultrasound: $300-500 depending on what part of the body and whether it is performed by a specialist or not.
- CT: Usually around $1500-2000.
- MRI: Around $3000-5000.
- Pathology reports/histopathology: The review of the sample is about $250-350 for a single site or sample. Keep in mind this does not include the surgery or process of getting the sample.
- Cytology: About $200-300 for a single site or sample.
- Blood work: Ranges depending on how comprehensive the panel is. A detailed full blood panel looking at liver values, kidney values, thyroid, and urine is often about $200-300. There are more basic panels with less information that can be lower in cost. Ask your veterinarian if this would be an appropriate option.
When Money is Tight
Diagnostics can be expensive, so your veterinarian will work with you to figure out the plan for staging and grading that works best for your unique situation with your dog.
- If a diagnostic test will directly change the type of treatment and that treatment is a financially, emotionally, and spiritually viable option for you, that test should be performed.
- If the test will not change treatment or the potential treatment is not affordable, then it may not make financial sense to perform it.
A veterinary oncologist is the best positioned to help you spend your money wisely. They will have the expertise and day-to-day experience to know which tests could be skipped in favor of treatment, for example.
Also, if certain testing is not within your spiritual, financial, or emotional bandwidth, alternative options or trial treatment with a suspected diagnosis in mind can be an option. However, the specific risks of treating in this fashion should be discussed with your veterinarian.
Hospice care or supportive care to help your dog feel better without direct treatment of the cancer is also sometimes an option. You will still need to work with your veterinarian to determine how the disease is impacting your dog’s life, which options are appropriate, and your dog’s quality of life as hospice continues.
Do I Need to Stage My Dog’s Cancer?
The advantage of staging and grading is that it helps you and your veterinarian understand your dog’s predicted lifespan and the best treatment options. It also informs us what to expect for quality of life.
Treating without full staging and/or grading can result in being too aggressive or not aggressive enough, and that can result in undesired side effects or lack of cancer control.
That said, flexibility and an open mind are essential both for the guardian and the veterinary team when dealing with cancer.
There are times when treating without all the information is necessary and a risk/reward assessment can help minimize negative outcomes.
There are also times when full staging or grading is not available or is not the best choice for you or your dog. In these cases, treatment and diagnostics may be tailored to accommodate individual circumstances.
In the end, you are the boss, and you know your dog best. Asking questions about what tests seem necessary and which could be skipped is not a sign that you don’t love your dog.
- Cancer staging fact sheet. Virginia Tech Animal Cancer Care and Research Center. https://cancercare.vetmed.vt.edu/content/dam/cancercare_vetmed_vt_edu/documents/cancer-fact-sheets/cancer_staging_fact_sheet.pdf. Accessed April 27, 2023.
- Cancer staging. National Cancer Institute. https://www.cancer.gov/about-cancer/diagnosis-staging/staging. Published October 14, 2022. Accessed April 27, 2023.
- Lymphoma in dogs. Washington State University Veterinary Teaching Hospital. https://hospital.vetmed.wsu.edu/2021/05/24/lymphoma-in-dogs/. Published May 24, 2021. Accessed April 27, 2023.
- Mouser P. Tumor grading-is it applicable? MSPCA Angell. https://www.mspca.org/angell_services/tumor-grading-is-it-applicable/. Published September 14, 2017. Accessed April 27, 2023.
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