Home » Pet Health » Cancer 101 » What are the Different Grades of Cancer?


Cancer grading broadly determines how much cancer is present in the body, its severity, location, and the extent to which it has spread. Grading helps cancer specialists devise a suitable treatment plan. Tumor grade describes a tumor based on how abnormal the cancer cells and tissue look under a microscope and how quickly the cancer cells are likely to grow and spread. A low-grade cancer grows more slowly and is less likely to spread than a high-grade one. Grading systems are different for each type of cancer and are useful indicators of cancer progression. Cancer grade is not the same thing as cancer stage. Stage refers to how large a cancer tumor is and how far the cancer has spread. The table below summarizes what the grades mean for most types of cancer:

Malignant Tumor Grading System

Grade Features
Grade 0 Cancer is present at the site of origin and has not spread to nearby tissues. It may be called in situ (‘in place’). This grade cannot be correctly assessed (undetermined grade).
Grade I The cancer is a small nodule and still exists at its location of origin. These cancer cells look very similar to normal cells but grow slowly (low grade).
Grade II The cancer has started to grow but hasn’t spread into the surrounding tissues. These cancer cells don’t look like normal cells and grow more quickly than normal (intermediate grade).
Grade III The cancer has grown significantly and has spread into nearby tissues and lymph nodes*. These cancer cells look very abnormal and are growing quickly (high grade).
Grave IV The cancer has spread to reach distant organs of the body. These cancer cells are the most abnormal-looking cells and grow and spread faster than any other grades (highest grade). This grade may also be called secondary, advanced, late-grade, or metastatic.

* Lymph nodes are small glands present throughout the body; they are responsible for filtering lymph from harmful substances, like viruses and bacteria, that travel through the lymphatic fluid (a clear-to-white fluid that circulates throughout the body and helps fight infections). Invasion into lymph nodes damages the body’s local immune system, allowing cancer to ultimately progress into grade four.

When you receive a cancer diagnosis for your pet, your vet will discuss the grade of your pet’s cancer and what treatment options are available that best suit your pet. It is crucial to diagnose cancer as early as possible because the tumor is smaller in the earlier grades, and there may be fewer cells, making its treatment easier. Early diagnosis enables treatment with much lower drug dosages or radiation therapy. Late-grade cancer is more challenging to treat since the cancer cells have most likely spread to different locations through the blood and lymphatic systems, have obstructed organs and impaired the immune system. Understanding these differences gives you the knowledge to decide what treatment will offer your furry friend a good quality of life and give you many happy tomorrows.

The Pet Cancer Foundation’s Website Editorial team is comprised of veterinarians, veterinary oncologists, and veterinary technicians, as well as scientific writers and editors who have attained their PhD’s in the life sciences, along with general editors and research assistants. All content found in this section goes through an extensive process with multiple review stages, to ensure this extended resource provides pet families with the most up-to-date information publicly available.

The team listing of those contributing to the information on this page is here:

Keep Your Pets Healthy Editorial Team

Last Updated: October 14, 2022

The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.

For reprint requests, please see our Content Usage Policy.

The Pet Cancer Foundation’s Medical Illustration team is comprised of medical illustration specialists and graphic designers that work in consultation with our team of experts to create the medical art found throughout our website. Though not all medical concepts require the assistance of imagery, when a page does contain a medical illustration, credit to the artist and our medical art director will be noted here.

The Pet Cancer Foundation’s medical imagery is protected by copyright and cannot be used without prior approval that includes a mutually signed licensing agreement.Please review our Content Usage Policy.

The following sources were referenced to write the content on this page: 

Telloni, SM 2017, ‘Tumor staging and grading: A primer’, Methods Mol Biol, vol. 1606, pp. 1-17.

National Cancer Institute, Tumor Grade (Updated, August 1, 2022), viewed Oct. 2, 2022, https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-grade

The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.

For reprint requests, please see our Content Usage Policy.