Grade and Stage of a Tumor in Your Pet
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Grade and Stage of a Tumor in Your Pet

by Rachel Venable, DVM, MS, DACVIM (Oncology)
Sep 27, 2023

The word “cancer” can be very scary to hear. Often when we are given this diagnosis in our animals, our brain freezes, and it is impossible to hear the rest of the information. It is still important to understand what the veterinarian is trying to tell you. Learning more about cancer can help you feel more informed and comfortable with your decisions throughout this difficult process.

What does a tumor stage mean?

We often hear people refer to their own cancers as stage II lung cancer or stage IV pancreatic cancer. But what does this actually mean? The stage of cancer is a designation of the level of disease in the body. This means it is a faster way for medical professionals to communicate how much cancer is truly in the body. The staging system can be different for different cancers. We do not always stage cancers in veterinary medicine but will instead use terms such as “no metastasis or no spread of disease, or there is spread to local lymph nodes or other organs like the lungs”.

  • Stage I often refers to tumors which are smaller in size (<2 cm) and have not spread to other parts of the body.
  • Stage II often refers to cancers that are larger in size (2-5 cm) and may or may not have local spread.
  • Stage III refers to cancers that are even larger in size (>4-5 cm) and/or have spread to regional lymph nodes.
  • Stage IV often refers to cancers which have spread to distant sites such as the lungs or other organs like the liver.
  • Stage five is when it is most advanced and a higher level in the body. Lymphoma is one of the few cancers that has a stage five.

The amount of cancer in the body is important because this can change what treatment options are possible and the prognosis. Cancers at a higher stage often cannot be surgically removed and may be treated with medical therapies or even palliative to hospice care. Tumors which are lower stage can often be treated with surgery alone.

Staging is performed with imaging such as x-rays, ultrasound, or CT scan. We can also stage by sampling the regional lymph nodes with a fine needle aspirate and cytology.

What is tumor grade?

Many people are confused by stage and grade. Grade is not something you hear people discuss as much when they talk about their own cancer. Also, not every tumor is graded. Grading is a score that a cancer is given when tissue is submitted to the lab and then analyzed under the microscope. This is called histology, and it is done by a pathologist. Cancers with an established grading scheme will be reported in the pathology report. Grade is often associated with prognosis.  Higher grade tumors are generally more aggressive and more likely to spread to other parts of the body, versus low-grade tumors are less likely to spread, and may not need as aggressive treatments.

A surgical biopsy is needed to determine grade. To determine the grade of a tumor, the pathologist will look for specific characteristics of the tumor cells, as well as how the tumor cells are affecting the regional tissue.

The Importance of Tumor Stage and Tumor Grade

Tumor stage and grade can go together when a pet has a high-grade tumor, which has already spread to other parts of the body, giving it a higher stage. Stage and grade are very important because they help determine treatment options and prognosis for your pet. As mentioned earlier, not every cancer has a formal staging system, so do not be upset if your veterinarian cannot tell you the exact stage. But after doing testing, you should know if there is any spread (metastasis) of the cancer in the body. Also, not every cancer has an established grading system. But you can ask your veterinarian if there is a grade for your pet’s cancer. The more knowledge you have about your pet’s cancer, the better you will be able to guide treatment and goals with therapy for your family.

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