Has the Cancer Spread and How Do We Find Out?

Determining whether cancer has spread is called staging. Staging helps the veterinary team understand how much cancer is present, where it is located, and whether it has traveled to lymph nodes, the lungs, abdominal organs, bones, or other parts of the body.

Not every dog needs every staging test. The recommended testing depends on the type of cancer, where it began, how likely it is to spread, and whether the results would change the treatment plan.

What Does It Mean When Cancer Spreads?

Cancer spreads when malignant cells leave the original tumor and establish new tumors elsewhere in the body. This process is called metastasis.

Cancer commonly spreads through:

• The lymphatic system

• The bloodstream

• Direct invasion into nearby tissues

• Body cavities, depending on the cancer type

The locations most likely to be affected vary by cancer. Some tumors commonly spread first to nearby lymph nodes, while others are more likely to spread to the lungs, liver, spleen, bones, or other organs.

Can A Physical Examination Detect Spread?

A thorough physical examination is an important first step. Your veterinarian may check:

• The size and location of the original tumor

• Nearby and distant lymph nodes

• The abdomen for enlargement or masses

• The mouth and skin for additional lesions

• Breathing sounds

• Mobility, pain, and neurological function

• Body weight and muscle condition

However, cancer can spread without causing obvious symptoms or abnormalities during a physical examination. Additional testing is often needed.

Bloodwork And Urinalysis

A complete blood count, serum chemistry panel, and urinalysis may be recommended to assess your dog’s overall health and look for changes that could suggest organ involvement.

These tests may reveal:

• Anemia

• Abnormal white blood cell counts

• Low platelet counts

• Liver or kidney abnormalities

• Elevated calcium

• Changes associated with internal bleeding

• Whether your dog may safely undergo anesthesia or treatment

Routine bloodwork usually cannot prove that a solid tumor has spread. Normal results also do not rule out metastasis. Blood and urine tests are generally used alongside imaging and tissue sampling.

Lymph-Node Sampling

Cancer may spread to the lymph nodes closest to the original tumor. Your veterinarian may recommend collecting cells from one or more lymph nodes using a fine-needle aspiration.

A lymph node does not have to be enlarged to contain cancer cells. Likewise, an enlarged lymph node may be reacting to inflammation or infection rather than cancer.

For this reason, size alone may not be enough to determine whether a lymph node is involved. Sampling the node can provide more useful information.

Chest X-Rays

Chest radiographs are commonly used to look for tumors that have spread to the lungs. They may also reveal enlarged lymph nodes within the chest, fluid accumulation, or another condition affecting breathing.

Chest X-rays are often taken from three views because small nodules may be easier to see from one angle than another.

However, microscopic metastases and very small lung nodules may not be visible on radiographs. A normal chest X-ray means that no visible spread was detected, not that microscopic cancer is impossible.

Abdominal Ultrasound

An abdominal ultrasound allows the veterinarian to examine structures such as the:

• Liver

• Spleen

• Kidneys

• Adrenal glands

• Intestines

• Bladder

• Abdominal lymph nodes

If an abnormal area is found, the veterinarian may recommend collecting cells or tissue with ultrasound guidance.

Ultrasound findings alone may not confirm metastasis. Benign nodules, age-related changes, inflammation, and cancer can sometimes look similar, so sampling may be necessary.

CT Scans

A CT scan creates detailed cross-sectional images of the body. It may detect smaller lung nodules or provide more precise information about a tumor’s size and invasion than standard X-rays.

CT may be especially useful for:

• Lung evaluation

• Nasal tumors

• Oral tumors

• Chest tumors

• Bone tumors

• Surgical planning

• Radiation planning

• Tumors in anatomically complicated locations

CT scans commonly require sedation or general anesthesia. Ask whether the additional detail is likely to change your dog’s treatment plan.

MRI Scans

MRI provides detailed images of soft tissues and is commonly considered when cancer may involve the:

• Brain

• Spinal cord

• Nerves

• Muscles

• Nasal cavity

• Other complex soft-tissue structures

MRI is not routinely needed for every cancer. It is selected when the tumor’s location or your dog’s symptoms make it useful.

Bone Scans And Bone Imaging

Some cancers are more likely to spread to bone or begin within bone. Your veterinarian may recommend targeted X-rays, CT, MRI, nuclear bone scanning, or other tests if your dog has:

• Persistent lameness

• Bone pain

• Swelling

• Unexplained fractures

• A cancer known to affect bone

The most appropriate test depends on the suspected cancer and the location of the symptoms.

Bone-Marrow Testing

Bone-marrow aspiration or biopsy may be recommended for certain cancers, especially some blood cancers, lymphomas, leukemias, or conditions involving abnormal blood cell counts.

This is not a standard staging test for every solid tumor.

Cytology And Biopsy

When imaging reveals a suspicious lymph node, organ, or mass, the veterinary team may recommend obtaining a sample.

Common sampling methods include:

• Fine-needle aspiration

• Core biopsy

• Surgical biopsy

• Endoscopic biopsy

• Bone-marrow aspiration or biopsy

Cytology examines individual cells, while histopathology examines tissue architecture. A biopsy may provide more information, but it can also be more invasive.

Does A Normal Scan Mean The Cancer Has Not Spread?

Not necessarily. Imaging can detect abnormalities only when they are large enough or distinct enough to be seen.

A dog may have:

• No detectable metastasis

• Microscopic metastasis that is too small to see

• Suspicious findings that cannot yet be confirmed

• Benign changes that resemble metastatic disease

Veterinarians may describe a dog as having no evidence of detectable metastasis rather than guaranteeing that no cancer cells exist elsewhere.

This distinction is especially important with cancers known to spread early.

Can The Cancer Spread After Staging Tests Are Completed?

Yes. Staging reflects what can be detected at a particular point in time. Cancer may spread or become visible later.

Your veterinarian may recommend repeating examinations or imaging:

• During treatment

• After treatment

• At scheduled recheck appointments

• When new symptoms develop

• If bloodwork changes

• If the original tumor returns or grows

The follow-up schedule should be based on the behavior of your dog’s specific cancer.

Which Tests Does My Dog Actually Need?

The ideal staging plan depends on:

• The exact cancer type

• Tumor grade

• Tumor location and size

• Known patterns of spread

• Your dog’s symptoms

• Your dog’s general health

• The treatment being considered

• Whether a test result would change your decision

For example, extensive staging may be important before a major surgery if discovering distant spread would change whether surgery is recommended. In another situation, a family may choose comfort-focused care regardless of the results and decide not to pursue every available test.

It is reasonable to ask what each test is intended to find and how the result would affect the plan.

Questions To Ask Your Veterinarian

• How likely is this cancer to spread?

• Where does this cancer usually spread first?

• Which staging tests are recommended?

• What is each test looking for?

• Could the result change the treatment plan?

• Should nearby lymph nodes be sampled even if they are not enlarged?

• Would chest X-rays be sufficient, or would CT provide useful additional information?

• Does my dog need an abdominal ultrasound?

• Will sedation or anesthesia be required?

• What are the risks and costs of the tests?

• What does a negative staging result actually mean?

• How often should staging tests be repeated?

• What symptoms could indicate that the cancer has progressed?

The Most Important Takeaway

The only way to evaluate whether cancer has spread is through a combination of physical examination, appropriate imaging, laboratory testing, and sampling suspicious tissues.

No single test can detect every cancer cell. Staging identifies the disease that is currently detectable and gives the veterinary team the best available information for planning treatment and estimating prognosis.

Ask your veterinarian to recommend a personalized staging plan and explain how each result could affect the options available for your dog.

References

Cornell University College of Veterinary Medicine. (n.d.). Diagnosis and staging. 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.). Oncology. https://www.vet.cornell.edu/hospitals/services/oncology

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

VCA Animal Hospitals. (n.d.). Lung tumors. https://vcahospitals.com/know-your-pet/lung-tumors

VCA Animal Hospitals. (n.d.). Malignant mammary tumors in dogs. https://vcahospitals.com/know-your-pet/mammary-tumors-in-dogs-malignant