What Does The Stage Or Grade Of My Dog’s Cancer Mean?

The stage and grade of a dog’s cancer describe two different aspects of the disease. Both can help the veterinary team estimate how the cancer may behave, choose appropriate treatments, and discuss prognosis.

In simple terms:

• Grade describes what the cancer cells look like and how aggressively they may behave.

• Stage describes how much cancer is present and how far it has spread.

A dog can have a high-grade tumor that has not yet visibly spread, or a lower-grade tumor that is advanced because of its size or location. Grade and stage should therefore be considered together rather than used interchangeably.

What Does Tumor Grade Mean?

Tumor grade is usually determined by a veterinary pathologist who examines tissue collected through a biopsy or surgery.

The pathologist evaluates microscopic features that may include:

• How closely the cancer cells resemble normal cells

• How abnormal the cells and their nuclei appear

• How quickly the cells are dividing

• Whether the tumor invades surrounding tissue

• How much inflammation or tissue death is present

• Whether cancer cells are visible in blood vessels or lymphatic vessels

• Other characteristics specific to that tumor type

The grade provides information about the tumor’s expected biological behavior. For some canine cancers, histologic grade is an important predictor of local recurrence, metastasis, and survival.

What Do Low, Intermediate, And High Grade Mean?

Although the terminology varies by cancer type, tumors may be described as low, intermediate, or high grade.

Low-Grade Tumors

Low-grade tumors generally:

• Resemble normal tissue more closely

• Have fewer actively dividing cells

• Grow more slowly

• Invade surrounding tissue less aggressively

• Carry a lower risk of spreading

• Have a more favorable prognosis

A low-grade tumor is still cancerous and may require treatment. It can recur if it is not completely removed, and its location may still create significant medical problems.

Intermediate-Grade Tumors

Intermediate-grade tumors fall between low- and high-grade disease.

Their behavior may be less predictable. Some remain controlled after appropriate local treatment, while others recur or spread. The tumor’s size, location, surgical margins, mitotic count, and staging results may become especially important when estimating prognosis.

High-Grade Tumors

High-grade tumors generally:

• Look highly abnormal under the microscope

• Have more actively dividing cells

• Grow more rapidly

• Invade nearby tissue more aggressively

• Carry a greater risk of recurrence

• Carry a greater risk of metastasis

• Require more extensive treatment or monitoring

Higher histologic grades have been associated with greater risks of recurrence and metastasis in cancers such as canine soft tissue sarcomas and mast cell tumors.

However, high grade does not automatically mean that treatment cannot help. The stage, location, ability to achieve local control, and response to therapy remain important.

Are All Grading Systems The Same?

No. There is no single grading system that applies to every canine cancer.

Different tumor types may use different systems. Examples include:

• Low, intermediate, and high grade

• Grade I, II, and III

• Two-tier systems using low grade and high grade

• Cancer-specific scores or classifications

For example, canine mast cell tumors may be classified using a three-tier system or a two-tier low-grade versus high-grade system. The grading system used should be named in the pathology report because the meaning of a particular number depends on that system.

A Grade II mast cell tumor cannot be directly compared with a Grade II soft tissue sarcoma or another cancer. Ask your veterinarian which grading system was used and what that result means for the specific tumor.

What Is The Mitotic Count?

The mitotic count estimates how many tumor cells are actively dividing within a defined area of tissue.

A higher mitotic count often suggests that the tumor is growing more quickly. It may contribute to the tumor’s grade and prognosis.

The report may describe the result as:

• Mitotic count

• Mitotic index

• Mitoses per high-power field

• Mitoses within a defined area of tissue

The number should not be interpreted alone. Its significance depends on the cancer type, grading system, and other microscopic findings.

Ask your veterinarian:

• Is the mitotic count considered low or high for this cancer?

• Did it affect the tumor’s grade?

• Does it change the recommended treatment or monitoring plan?

What Does Cancer Stage Mean?

Cancer stage describes the extent of disease within the body.

Depending on the cancer, staging may consider:

• The size of the primary tumor

• Whether the tumor has invaded nearby tissues

• Whether regional lymph nodes contain cancer

• Whether distant organs contain detectable metastases

• Whether multiple organs or body regions are involved

• Whether the cancer is causing systemic illness

• Whether certain cancer-specific clinical features are present

The AVMA summarizes stage as how large a tumor is and how far it has spread to other areas of the body.

How Is The Stage Determined?

The staging process may include:

• A complete physical examination

• Measurement of the primary tumor

• Complete blood count

• Serum chemistry panel

• Urinalysis

• Fine-needle aspiration of lymph nodes

• Chest X-rays

• Abdominal ultrasound

• CT or MRI

• Bone imaging

• Bone-marrow testing

• Sampling of suspicious organs or lesions

The exact tests depend on the cancer’s expected behavior and pattern of spread. Cornell notes that staging and clinical evaluation may involve laboratory testing, radiographs, advanced imaging, and tissue sampling as appropriate for the individual tumor.

Not every dog needs every test. Ideally, each test should answer a meaningful question or have the potential to change treatment recommendations.

What Is The TNM System?

Some cancers are staged using a system based on:

• T — Tumor: The size and local extent of the primary tumor

• N — Nodes: Whether regional lymph nodes are involved

• M — Metastasis: Whether the cancer has spread to distant locations

For example, a small localized tumor with no lymph-node involvement and no detectable distant spread would generally have a more favorable stage than a large invasive tumor involving lymph nodes and distant organs.

However, the TNM definitions differ by cancer type. The same measurements or lymph-node findings do not produce the same stage for every tumor.

What Do Stage I, II, III, IV, Or V Mean?

Many staging systems use Roman numerals, but the meaning of each number depends on the cancer.

In general:

• Earlier stages usually indicate more localized disease.

• Later stages usually indicate larger tumors, lymph-node involvement, distant spread, or more extensive disease.

However, there is no universal rule that Stage III or Stage IV means exactly the same thing for every canine cancer.

For example, lymphoma commonly uses a five-stage system based on the number and location of affected lymph nodes and organs. Solid tumors may use different systems based on tumor size, local invasion, lymph-node involvement, and metastasis.

Always ask for an explanation specific to the diagnosed cancer rather than relying on the stage number alone.

What Is A Cancer Substage?

Some cancers include a substage based on whether the dog is showing signs of illness.

For example, lymphoma may be described as:

• Substage A: The dog is not showing significant illness related to the cancer.

• Substage B: The dog is experiencing clinical signs such as poor appetite, lethargy, weight loss, vomiting, diarrhea, or other systemic symptoms.

Substage can sometimes provide additional prognostic information and help the veterinary team assess how urgently supportive care is needed.

Can A Dog Have A High-Grade, Low-Stage Cancer?

Yes.

A high-grade, low-stage tumor may appear aggressive under the microscope but remain confined to its original location at the time of staging.

This situation may lead the veterinary team to recommend:

• Aggressive local treatment

• Wider surgery

• Radiation therapy

• Chemotherapy to address possible microscopic spread

• More frequent follow-up examinations

• Repeat imaging

The fact that no visible metastases were found is encouraging, but the high grade may indicate a greater risk that microscopic cancer cells are already present elsewhere.

Can A Dog Have A Low-Grade, High-Stage Cancer?

Yes, although the meaning depends on the cancer.

A lower-grade tumor may grow slowly but become locally extensive over time. It may also occur in a difficult location or involve lymph nodes or another structure before it is detected.

A slow-growing tumor can still be serious if it:

• Presses on the brain or spinal cord

• Blocks the airway

• Interferes with eating

• Invades bone

• Obstructs the urinary or digestive tract

• Cannot be surgically removed

• Causes pain or organ dysfunction

Grade describes microscopic behavior, not necessarily the practical difficulty of treating the tumor.

Does A Higher Stage Always Mean A Poor Prognosis?

A higher stage generally indicates more extensive cancer and may reduce the chance of cure. However, it does not always mean that treatment is futile.

The outlook depends on:

• The cancer type

• Where the cancer has spread

• The amount of metastatic disease

• Whether the spread is causing symptoms

• Available treatments

• The dog’s general health

• The cancer’s response to therapy

• The goals of care

Some advanced cancers can respond well to systemic treatment and enter remission. Other cancers may be difficult to control even when discovered at an earlier stage.

Does A Low Stage Mean My Dog Is Cured?

No. A low stage generally means the cancer appears localized based on the tests performed.

Imaging and sampling cannot detect every individual cancer cell. Microscopic disease may be present even when scans and lymph-node samples appear normal.

Veterinarians may therefore use language such as:

• No detectable metastasis

• No evidence of metastatic disease

• Clinically localized disease

These terms mean that spread was not found with the available testing. They do not guarantee that metastasis will never develop.

Can The Stage Change?

Yes. Cancer stage reflects the disease at a particular point in time.

A dog’s stage may change if:

• The primary tumor grows

• A lymph node later tests positive

• New lung nodules appear

• Cancer develops in another organ

• Previously microscopic disease becomes detectable

• Additional diagnostic testing provides new information

The veterinary team may repeat staging tests during or after treatment to determine whether the disease is stable, responding, or progressing.

Can The Grade Change?

The original grade is based on the tissue that was examined at the time of biopsy or surgery. It generally remains part of the tumor’s permanent pathology record.

However, tumors can contain areas with different microscopic characteristics. A small biopsy may not always represent the entire mass. A recurrent tumor may also show different features when sampled later.

Research has evaluated changes in histologic grade between original and recurrent canine soft tissue sarcomas and mast cell tumors, illustrating that grade assessment can sometimes vary with sampling or recurrence.

A second pathology review may be appropriate when:

• The grade is uncertain

• The sample was small

• The report is inconsistent with the tumor’s behavior

• The grade will significantly affect treatment

• The cancer has returned

• Another specialist recommends review

Which Is More Important: Stage Or Grade?

Neither is universally more important. Their value depends on the cancer type.

For some cancers, grade strongly predicts the risk of recurrence or spread. For others, stage, tumor size, location, molecular markers, or response to treatment may be more important.

The veterinarian may also consider:

• Surgical margins

• Mitotic count

• Lymphatic or vascular invasion

• Tumor subtype

• Genetic or molecular markers

• Your dog’s symptoms

• Overall health

• Response to treatment

Ask the oncologist which factors are most useful for predicting your dog’s outcome.

How Do Stage And Grade Affect Treatment?

Stage and grade may influence whether the veterinary team recommends:

• Surgery alone

• Wider or repeat surgery

• Chemotherapy

• Radiation therapy

• Targeted medication

• Immunotherapy

• A combination of treatments

• Active monitoring

• Palliative care

For example:

• A localized, low-grade tumor removed with adequate margins may require monitoring only.

• A high-grade tumor may prompt discussion of chemotherapy even when no visible metastasis is present.

• A tumor involving nearby lymph nodes may require treatment of both the primary site and the lymph nodes.

• Distant metastasis may shift the focus from local surgery to systemic or palliative treatment.

How Do Stage And Grade Affect Prognosis?

In general, lower-grade and earlier-stage cancers tend to have more favorable outcomes than higher-grade and more advanced cancers.

However, prognosis also depends on:

• Tumor type

• Tumor location

• Surgical margins

• Ability to complete treatment

• Response to treatment

• Existing medical conditions

• Quality of life

• Whether complications develop

No grade or stage can predict exactly how long an individual dog will live.

Questions To Ask Your Veterinarian

• What is my dog’s exact cancer type?

• What grade is the tumor?

• Which grading system was used?

• What microscopic findings determined the grade?

• What is the mitotic count?

• What does this grade mean for recurrence and metastasis?

• What stage is the cancer?

• Which staging system was used?

• What tests were used to determine the stage?

• Were the regional lymph nodes sampled?

• Was any metastatic disease found?

• Could microscopic spread still be present?

• Do we need additional staging tests?

• Which is more important for this cancer: grade or stage?

• How do the stage and grade affect treatment?

• How do they affect prognosis?

• Should the pathology be reviewed again?

• How often should staging tests be repeated?

• What symptoms could indicate progression?

The Most Important Takeaway

Grade and stage answer different questions.

Grade asks: How aggressive does the cancer appear under the microscope?

Stage asks: How much cancer is present, and where is it located in the body?

Together, these findings help the veterinary team estimate the risk of recurrence or spread, choose treatment, and discuss prognosis. However, they are only part of the overall picture.

Ask your veterinarian to explain the grading and staging systems used for your dog’s specific cancer. The most useful interpretation combines the pathology report, staging results, tumor location, surgical margins, your dog’s overall health, and the goals of care.

References

American Veterinary Medical Association. (2025). Cancer in pets. https://www.avma.org/resources/pet-owners/petcare/cancer-pets

Cornell University College of Veterinary Medicine. (n.d.-a). Diagnosis and staging. Retrieved July 16, 2026, from https://www.vet.cornell.edu/departments-centers-and-institutes/sprecher-institute-comparative-cancer-research/treatment-strategies/diagnosis-and-staging

Cornell University College of Veterinary Medicine. (n.d.-b). Oncology. Retrieved July 16, 2026, from https://www.vet.cornell.edu/hospitals/services/oncology

Cornell University College of Veterinary Medicine. (n.d.-c). Soft tissue sarcomas in dogs. Retrieved July 16, 2026, from https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/soft-tissue-sarcomas-dogs

Griffin, M. A., Hughes, K., Altwal, J., Seguin, B., & Wustefeld-Janssens, B. (2023). Grade shifts in recurrent canine soft tissue sarcomas and mast cell tumors. Journal of the American Veterinary Medical Association, 261(9), 1284–1290. https://doi.org/10.2460/javma.23.01.0050

Sabattini, S., Scarpa, F., Berlato, D., & Bettini, G. (2015). Histologic grading of canine mast cell tumor: Is 2 better than 3? Veterinary Pathology, 52(1), 70–73. https://doi.org/10.1177/0300985814521638

VCA Animal Hospitals. (2024). Mast cell tumors in dogs. https://vcahospitals.com/know-your-pet/mast-cell-tumors-in-dogs